When we bought our bus last summer it had no house battery bank or inverter installed – critical features of utmost importance for two Technomads who depend on ample electricity for both our work and social lives.
We knew this was an area we needed to immediately address if we wanted any sort of autonomy on the road other than strictly living pole-to-pole. And with a week in the desert without any access to hookups camped at Burning Man looming ahead of us, we knew we had to figure out our electrical plans quickly.
The safe, simple, and sane option would have been buying a moderately sized bank of AGM batteries and a basic run-of-the-mill Inverter/Charger.
But, what’s the fun in that?
Instead – we jumped into the deep end of battery geekery, and decided to go lithium.
(Specifically – we went Lithium Iron Phosphate aka LFP aka LiFePO4)
But in the RV market (as opposed to the more common electrical vehicle – EV – applications), lithium remains a fairly new experimental playground. Relatively few other pioneers have begun playing with this technology for building house battery banks.
And after all, if faced with a choice between cool next-generation unproven technology or a well known traditional choice, what else should self respecting Technomads pick???
Pulling An All-Nighter Rewiring Our Bus
So we decided to go for it, and after a mad dash all-night installation push we managed to get our new batteries and inverter installed just in time for Burning Man last year, with only minutes to spare.
And, amazingly, everything worked.
Not only worked for our bus, but for powering a friend’s bus with a failing generator at Burning Man too!
And with only a few hiccups along the way, things are still purring along nicely a year later.
But, a year later, do we still think that it was really worth it to spend nearly as much on an electrical system as we did on buying our bus in the first place?
How has our first year on lithium been? Would we do it again?
Have there been challenges? What have we learned along the way?
With a year’s experience under our belt, here’s some of what we’ve learned…
Getting Charged Up
A 12V lithium battery is made up of four cells in series, with a nominal cell voltage of 3.2+ volts/cell. This is in contrast to a common lead acid battery, which is crafted from six 2.1 volt cells. The end result of these cells in series is that a fully charged lithium battery has a higher resting voltage (13.4V) than a lead acid battery (12.6V), but the two battery chemistries are close enough in operating voltage to be mostly compatible.
Mostly.
EMS Display While Charging
One of the challenging differences is that lithium batteries ideally prefer a slightly different charging profile than commonly found in chargers designed for lead acid batteries – and only a couple inverters or chargers have a pre-programmed “Lithium” setting yet.
Instead, there are usually just the traditional presets for Flooded, AGM, and Gel.
You can probably get away with using one of these presets (and some lithium battery makers sell batteries intended to be “drop in” replacements for regular AGM’s), but one of the primary reasons we went with our fancy Victron inverter and control panel is that it let us manually set a charging profile for our batteries – disabling temperature compensation, setting a target charge voltage, and letting us play around to find an ideal float voltage. It even let us set very low charge currents for our balancing experiments. (See below for more on balancing.)
But even the Victron proved slightly less than ideal when it came to charging. LFP batteries can be bulk charged to nearly 100% capacity and do not need an extended absorption phase, but even the Victron would not let us set an absorption time to anything less than 1 hour.
Still that was close enough to ideal that we’ve been able to come up with a charge profile that has been working reliably for the past year.
Our current charge settings are bulk / absorption charge to 14.2V, absorb for 1 hour (we can’t lower this), and then float at 13.6V. We have temperature compensation, equalization, and battery “storage mode” features disabled as well.
The Victron charger is rated at 120A charge current, but we’ve never managed more than 111A out of it. With that we can usually fully charge mostly depleted batteries in just 3 or 4 hours of generator time, and there is no need for extended run-time waiting for a slow absorption phase to finish topping off the final 20% of the batteries.
When we do add a solar controller to the mix, we will also be sure to seek out a fully programmable one so that we can make sure that it matches our charge parameters well.
One other note – I’ve noticed that the batteries do not get roasting hot when they are charging at this rate, thanks to LFP’s low internal resistance.
Overall – charging hasn’t proven to be much of a problem at all.
Raw Cells
Four Cells? Or Twenty? If you look into our battery bay, you will see twenty blue boxes (roughly the size of cereal boxes) – all strapped and bolted together into a single large (but light 140lbs!) slab. Each of these boxes is a 3.2V 100Ah LFP battery cell from Elite Power Solutions.
These cells initially came bolted together as a 4-pack, thus forming a single 100Ah 12.8V battery.
Our Battery: 4x 500Ah 3.2V “cells” in series, each made of 5x 100Ah 3.2V individual cells in parallel.
To build our desired 500Ah 12.8V battery bank, we disassembled five of these batteries, and reassembled four banks of five modules wired in parallel to build several larger 500Ah 3.2V cells.
Then we chained four of these “cells” in series to make our battery bank.
We did it this way to give the EMS one battery with four cells to monitor. If we hadn’t constructed this single large slab, we would have needed a separate EMS and set of sense boards for each of the five separate batteries.
This is how we can simultaneously have both twenty and just four cells in our system.
EMS Goodness & Glitches
Though it is not strictly required, it is generally considered a good idea to pair a lithium battery bank with some sort of an energy management system (EMS) to protect the expensive battery bank from accidentally being over-charged or over-discharged, both of which can cause permanent and maybe even unrecoverable damage to LFP batteries.
Installing the EMS Sense Boards
We purchased an EMS from Elite Power Solutions along with our battery cells. The EMS consists of a control module, as well as a chain of four small sense boards that attach to the four battery cells.
The EMS measures the voltage across the entire battery pack, as well as across each of the cells. It also measures the individual cell temperatures, the overall battery state of charge (as a percentage), and the charge/discharge current. All of this information can be displayed via a composite TV-out cable that we either hook up to our backup camera monitor, or display on our computer monitor via a video capture card.
The EMS has two alarm wires that can be triggered – the high voltage alarm triggers if any individual cell reads over 3.7V, and the low voltage alarm triggers if any cell drops below 2.8V. And both alarms trigger if there is some sort of runaway high temperature situation.
These alarm wires were initially connected to two Tyco EV200 Contactors that could completely disconnect the battery in the event of an alarm situation, saving the battery from harm. I’ve now modified the system so that one contactor works as a battery disconnect wired up to the alarms, and the other can be triggered to bridge in current from the bus’s engine alternator to charge our batteries and/or run a roof AC while we are underway.
The EMS has done its job admirably protecting our batteries (especially the one time we left our bus for several days to attend to a family medical situation, and the shore power breaker tripped when our driveway surfing host plugged in a space heater inside on the same circuit!), but the EMS hasn’t been without issues.
The Elite Power Solutions EMS CPU Module
For one – all the settings are programmable, but only by sending the EMS back to Elite Power Solutions. I wish there was a way that a user could adjust the alarm triggers or installed battery capacity more easily. As you will see in the section on balancing below, this resulted in a bit of a headache for us.
I also discovered that overall EMS pack voltage readout always reads roughly 0.36V higher than it should – a small issue that in cooperation with Elite we discovered was because the EMS had initially been calibrated for a much higher voltage battery backs (96V or higher is common in electric vehicles) than the 12.8V target nominal voltage in our system.
The EMS UI also has a few display bugs – all of which have reportedly been fixed now.
At some point we plan to send our EMS back in to Elite for reprogramming and upgrading the internal software, hopefully solving all of these issues.
Finding Balance
One areas where the EMS became a problem was in initially balancing our battery cells.
In a battery – ideally all the cells should be balanced, charged with exactly the same voltage and having an identical capacity. Usually when a battery “dies” it is because a single cell has gone bad and is no longer a match for the others.
Theoretically, when we purchased our cells they were all supposed to be matched and pre-balanced, but we did not have time to use Elite’s test equipment to confirm this when we first worked with them to build our battery bank.
Cells Out Of Balance – Min: 2.89V, Max: 3.22V
When I finally did have time to do some testing of my own, I discovered that we were getting substantially less capacity than I expected as a result of the cells being a bit out of balance. As a result, our 500Ah battery was only able to deliver 420Ah before triggering the low voltage cutoff in the EMS system, shutting the batteries down.
The EMS sense boards on each cell have a built in balancing shunt circuit that was supposed to make balancing our cells easy. The shunt engages when the cell reaches 3.7V, and the green light on top of the sense board turns red as a 1/2A balancing load is placed upon the cell.
Assuming you are charging slowly enough so as not to overwhelm the shunts (and this is another place the Victron’s programability comes in handy) you can very slowly and carefully charge your battery bank to 14.8V (3.7V x 4) and the shunts will hold down the out of balance high cells until all the cells are balanced and equal.
This is how it was supposed to work.
But every time I tried, the EMS would end up triggering a high-voltage alert and disconnect the battery after 30 seconds. Often it seemed as if the EMS was disconnecting the batteries before the shunt even began to do any work.
I eventually traced down the problem — the EMS was programmed to disconnect the battery 30 seconds after it detected a 3.7V reading on any cell. But the voltage metering of the cells was off slightly – the EMS would register a cell as being 0.03V – 0.05V higher than they actually were. A trivial amount, but it caused the EMS to disconnect the battery when a cell reached 3.65V, before the balancing shunt ever had a chance to engage at 3.7V.
Elite recognized the problem, and they have since redesigned the shunts to trigger at 3.55V, and for applications like ours they now recommend changing the EMS over-voltage alarm to trigger at 3.8V. This should give ample enough headroom for balancing to occur without the EMS disconnecting the entire bank.
Perfectly Balanced Cells (factoring in metering errors)
With the problem identified (and not wanting to deal with sending the EMS back to Elite), I set about to manually balance our cells by using alligator clips and an incandescent 12V bulb. I used the bulb to put a load on the high cells, and over the course of several days of trial and error I was eventually able to manually bring the cells into perfect balance.
It was annoying – but also educational.
And now a year later, I’ve just run through a series of load tests and manually tested the cell balance with a multimeter at various states of charge, and it looks like our cells haven’t drifted out of balance at all in the past 11 months.
Capacity: You Can Never Have Too Much Juice
An RV power system requires balancing three variables – storage capacity, power consumption, and power generation.
In our past home-on-wheels, we achieved an elegant balance having just enough solar and storage capacity combined with an extreme focus on energy efficiency such that we barely ever even needed to think about running a generator unless we absolutely needed some air conditioning.
The Victron Control Panel Interface
We aim to eventually reach a similar balance point with our bus, but at the moment we still have a long way to go before we reach anything close to an elegant energy balance – we can only tackle so many bus projects at a time!
On the generation side, we still plan to install 500W – 1000W of solar on the roof, ideally as much as we can manage while preserving Zephyr’s aesthetics and elegant curvy lines. This much generation capacity should keep us from needing to run a noisy and unpleasant generator very often. We’re still deep in research on what our ideal choice for parts are, and will of course share that project as it progresses.
We also aim to work on enhancing (or even replacing) our generator to make it much less noisy and unpleasant, for the times when we do need to use it. No amount of solar will ever be able to keep up with air conditioning demands.
On the conservation side – we intend to soon replace our interior lighting with LED’s, eliminating one of our most substantial loads. We are also researching more power efficient air conditioning units (look for a future article on this topic), and we have replaced our propane traditional RV fridge (horribly inefficient when run on electricity) with an energy efficient marine-style Vitrifrigo 12V fridge.
As for capacity…
When we set out building the system last year the goal was to have enough battery capacity to run a roof AC (and all our other onboard systems) for “almost 3 hours on a charge”, allowing us to run errands on hot summer days while leaving the cat basking in cool comfort inside.
Why go lithium? For the cat, of course.
Yes, it is always all about the cat.
And the system has admirably lived up to calculated expectations – just this week I did a capacity test and managed 2hrs 42min of runtime with the AC on max-cool with high fans, and with all our other usual computers and lights on.
With the fans lower and especially with the thermostat turned down to allow the compressor to cycle, we would get substantially more runtime.
I have the inverter programmed to cut off before the EMS low-voltage alarm triggers to ensure battery longevity (even lithiums don’t like going too far below 80% drained too often) and because I have the EMS set up to require a manual reset if the low-voltage alarm is triggered (to make sure that if there is a problem, we know about it). In this test, the battery was at 16% capacity and 424Ah had been consumed when the inverter shut down. The overall bank voltage was still at 12.52V, well above the EMS warning line.
Ultimately, we know that we want more than 500Ah of battery on board – we just didn’t want to invest that much upfront last year until we had some chance to test out the technology further.
But now that we are sufficiently happy with how lithium has performed, we are ready to invest in more.
With a 1000 – 1200Ah battery bank (particularly coupled with a more energy efficient AC unit) we should have enough battery capacity to run the air conditioning over night when we are traveling and boondocking places where a generator would be frowned upon. This would also give us more days of autonomy with non AC loads, because even once we have solar there will still be days with minimal sun.
To upgrade our system – we would either expand our current battery bank to double the capacity, or if we find the right home for our current bank we would be open to selling it and starting from scratch. Though LFP batteries are theoretically OK with mixing older and new cells (better than lead acid, anyway), it would still be ideal to try and keep all the cells identically aged.
So… If you are interested in a totally awesome, well tested and fully functioning 500Ah lithium battery bank sometime in the next year, let us know. *grin*
Boosting Awesomeness & Inverter Oddities
Victron MultiPlus Inverter / Charger
We’ve only had an opportunity to live fully off-grid on a handful of occasions in the past year, so our batteries haven’t had too many deep cycles to really stress test them.
But where we have gotten plenty of use out of our electrical system has been using the boosting power of our inverter to make driveway surfing easy, allowing us to without worry run heavy loads like air conditioning or microwaves on dinky 15A circuits. Using our inverter’s power boosting feature to combine battery capacity with shore power allows us to stay places comfortably that would otherwise be near impossible.
Being able to limit shore current demands and boost when necessary are such incredibly useful features that I would never want to own an inverter that lacks these features.
Unfortunately, there aren’t very many inverters that can do this. Our Victron MultiPlus 3000VA is one of the only options out there.
After a year of heavy use, we remain mostly impressed with it – the overall most annoying issues we’ve discovered (discussed in this other post) is that the shore current limit can’t be set below 15A.
I’ve also noticed that the inverter is incapable of giving “just a little boost”, and this wastes energy and needlessly drains battery capacity.
For example, often we only need an extra amp or two of AC power (commonly needing a total draw of 17A with a 15A shore limit), but when the Victron’s Power Boost engages it drops the shore power load to 10A and makes up the entire difference off of the batteries, drawing 50A of DC and draining more capacity than would otherwise be needed.
95% Remaining – Warn Low Battery?!?!
One lithium-related area that is most annoying is that our Victron constantly thinks that it is suffering from a “low battery” condition when used with our lithium bank. This low battery warning is triggered when the inverter senses a battery voltage 1V above the programmed low voltage cutoff, but since lithium sags so little as it is being drained the inverter essentially always thinks that it is low when it is in use – even though the Victron battery monitor shows 90%+ capacity remaining.
The Victron battery monitor also has its share of lithium-unfriendly features. For example – it handily calculates a “time remaining” display to let you know how much longer you can keep running the current load — before the battery reaches 50% capacity. This is a fine target cutoff point for lead-acid, but I wish I could program this calculation to target our preferred 80% capacity cutoff point.
Alas, this is not programable.
Another battery monitoring issue I am trying to understand is that the battery monitor seems to incorrectly calculate its percentage remaining – overestimating how much capacity remains. The monitor knows we have a 500Ah battery, but as an example – during my last capacity drain test the Victron battery monitor indicated at one point that -280.6Ah had been consumed, but that a battery percentage remaining was 52%. I’m not sure how they can determine that a battery that has been 58% drained has 52% remaining – I am still hoping to get an answer from Victron support explaining this.
One final issue that we’ve discovered with the Victron – when it overloads (for example – we accidentally try and start two AC units at one time) the inverter is supposed to auto-reset when the error condition goes away, and sometimes it does. But other times, it fails to auto-reset and must manually be switched on/off in the battery bay to get it to restart.
Annoying, but fortunately a rarely encountered problem.
Alternate Power
Zephyr’s hefty 220A alternator was sized to power the big AC blowers when the bus was in passenger service. But at our normal 1500RPM cruise, the alternator can barely keep up with the 150A demands of our roof air.
One upgrade to our electrical system I completed earlier this year (just before we set off from Florida to spend the summer roaming) was setting up a bridge between our bus alternator and the battery / inverter – primarily so that we can run the roof AC while underway without constantly needing to run our annoying generator.
We probably wouldn’t have survived driving in the summer without this bridge in place.
Unfortunately though – the bus alternator at our typical driving RPM’s runs roughly just a tad below break even with the demands of the inverter and roof air conditioner while underway, meaning that if we run the AC full blast we can reach our destination with a partially depleted battery after a day of driving.
If on the other hand we can make due without full AC, the alternator is plenty hefty enough to fully charge our battery after just a couple hours on the road. This comes in quite handy if we’re planning to dry camp overnight, we arrive with a fully charged battery and know it will be refilled quickly when we hit the road the next day. This has been fitting nicely with our goal of only driving a couple hours a day.
Ultimately I’d like to increase our engine power generation capability and/or switch to a more energy efficient roof AC unit so that we always run at a net positive.
Any Other Annoyances?
We now spend more time showing off our battery bank than we do working on it. This is a good thing.
Setting up a battery system like ours may sound like a lot of intimidating work, but it really hasn’t been too hard at all.
And the best part – once it is built and configured (and balanced!) it for the most part has “just worked” and not been an issue at all.
It is nice having an electrical system that we feel as if we can rely on.
Lately, the biggest chore involving the battery system has been the need to constantly hoist my toolbox and parts bins out of the way to show our system off… *grin*
The real payoff from a lithium battery bank comes over time, and ideally this system is designed to last for years (decades even) of trouble-free service. Over the past year lead battery costs have gone up (by about 10% it seems) but the price of LFP batteries have remained constant, making the math even more appealing if we were starting out now.
So we’d certainly still go lithium if we were starting again from scratch.
But…
Ask us again next year. And the year after.
But, I somehow doubt we’d change our mind.
Not unless a battery technology even cooler comes along that is!
By the way, we should note — we are not trying to motivate anyone to follow us on this path. We are not selling these batteries, we are not affiliates with any battery dealer, we paid for all our components and nor do we have any financial stake in the technology beyond our own systems. We are simply full time RVing technomads who are designing our own cutting edge home & office on wheels, and are sharing our research & project. Of course we’d love to have more folks out there pioneering and helping us take the arrows in our backs. Right now, we do not consider this technology ready for the mainstream, and those contemplating this technology need to be a bit savvy with electrical and battery technology.
Chris I have a perplexing inverter issue that I hope you can shed some linght on. My Oliver Legacy Elite II came from the factory with 320 watts of solar, four Trojan T105 batteries, and a 2000 watt Xantrex inverter. The inverter shuts down at eleven volts even though the batteries still have over 80% amp hours left. When the inverter shuts off the battery volrage will immediately jump to over 12. Start the inverter again and the same thing happens. I took the batteries to a Trojan master distributer who put them on a load device overnight and the batteries are perfect.
Contacting Oliver for support of the system you paid them to install is your best bet. We haven’t run lead acid since our own Oliver days, as evidenced by the very post about Lithium you’re commenting on 🙂
I’ve heard of conversion kits to do this – but have never researched them. In yacht building, a lot of times custom shaped freezers are built to fit the shape of the hull – maybe you can check for further resources there. That might be a great idea for a bus conversion starting from scratch.
I don’t remember to do it all the time but it is a really good idea to to take your rings off when working with electricity, even a top quality gold ring can get pretty damn hot if it gets enough current through it..
Don’t leave out necklaces that can dangle onto the terminals while you are working. It’s not a bad idea to tape the shank of screwdrivers so they aren’t long metal sticks. The same goes for any wrenches that are long enough to short terminals if they slip out of your hand while you’re working around (not even just on) the battery pack.
Chris, have you hooked your lithiums to the alternator for charging while driving? I have a 400 Ah lithium pack and am concerned about it burning the alternator out demanding too much – is that a real worry and if so, do you have a solution. I have a Sprinter van based rv (diesel) with a regulator built into the alternator.
Thanks, Joe
You will have to check into the specs on your alternator. Our heavy-duty bus alternator is designed to run at full-output non-stop, and is great for charging up our batteries underway. I’m not at all familiar with the setup in the Sprinter however.
Your power management box should be able to be programmed so you won’t exceed the capability of your alternator when charging. I think I remember reading that in the Victoreen spec sheet when I was doing some research last year. The cheapest option is charging up while you’re plugged into AC. Using diesel to recharge is expensive unless your schedule has you off the grid for a while. Even though you might think that it isn’t anything extra since the bus motor is so big, looked at in terms of kWh units, it’s expensive. If you will be paying for a slot with hookups, get your monies worth and top up the battery pack.
Obviously, if we know we are heading to a campground with electric, we don’t worry about it and just plug in when we get there. But we very frequently live off-grid for extended periods of time, and charging while underway inbetween boondocking locations is awesome and a very cost effective to top off the battery banks. Certainly much cheaper than running the diesel generator if the sun can’t keep up with our solar setup…. or paying for a generic and boring ‘RV Slot’ just to get an electric hook-up.
Mark Csays
Hi Chris! Over the past 15 years I built out a 40-foot bus with a Detroit Diesel with the 270A gear driven alternator. I am also considering running my air conditioning using the bus alternator + inverter. Now, I think I know what may be causing your net battery drain when running your AC on inverter power with the bus alternator trying to keep up: your external voltage regulator sense wires need to go directly to your battery terminals. If your engine is like mine, it has a crappy old-school external voltage regulator the size of a shoe box with early TO-3 transistors. These old regulators go out of spec and require frequent adjustment. Get rid of it. I replaced mine with a modern external regulator designed for a fairly high-current field winding. It’s a pretty generic regulator I got for less than $20, and is rated for at least twice the field winding current of the bus alternator (which is not very much- I think about 8 amps). The new regulator is much smaller and rated for a 20+ amp field winding. It keeps the battery voltage constant at 14.1V charging voltage, and has never failed now going on 10 years and 20,000 miles. The important thing is that the regulator needs to sense the actual voltage of the battery it is trying to charge, not anywhere else in the system, as the high load current from your inverter (with air conditioner running) will cause a significant voltage drop through your cables that prevents your battery from getting charged properly. No matter how heavy gauge your cables are, you will always have a voltage drop when you draw that much current through them. What happens is the regulator thinks it’s keeping a battery at 14.1 volts but in fact, it is keeping some cable terminal or the alternator output at 14.1 volts while the battery voltage could be less than it needs to maintain charge. Connect the voltage regulator at the battery bank itself, and run the field output back to the engine alternator.
The voltage regulator is wired directly to the starter battery terminals – but the house lithium battery was formerly 25′ further forward and indeed, as expected, much of the loss was due to that long wire run.
I’ve more recently relocated the house batteries to be nearly adjacent to the starting batteries – and that has made a huge difference.
Replacing the 50 year old voltage regulator with a smarter and more modern design is on the todo list too. I’ll get around to that project one of these days.
I hadn’t realized how cheap modern replacements were – I might have to look into that sooner rather than later!
Awesome. With the house batteries located next to the starter batteries can you now run your roof AC while driving and keep all batteries maintained too?
I’m planning to do things differently on my bus…
I’m going to install a second inverter at the bus alternator that will act like a second generator input in my system. The inverter is set up to turn itself on only when the engine is running, and turns itself off when the engine stops. This inverter will be sized large enough to run the roof AC as well as the house battery charging equipment that converts AC power into a DC charge profile. The output of this inverter goes into a relay-type automatic transfer switch just like you would have for a generator set.
When the engine turns off and the engine inverter switches off, the transfer switch enables a second inverter to power all the house alternating current needs with the exception of the roof AC and battery charging equipment. This second inverter is selected to be more efficient than the one connected to the engine alternator, because it runs off the house battery system and needs to conserve power. However, it does not need to produce as much output because it only runs the smaller house appliances.
A similar transfer switch relay is installed that allows shore power to override all other AC power inputs and also energize the roof AC and battery charger.
What I like about this system is that the house batteries get charged with the power converter charger and not directly off the engine alternator- I find that this set-up regulates the charge profile a lot more accurately and gets the batteries charged faster as well. Also, I am not relying on my house inverter to run the roof AC. I use a cheaper brute-force inverter to run the roof AC directly off the bus alternator current. Keeps the systems isolated too- I never have the starter batteries connected to the house batteries this way.
VOLTAGE REGULATOR INFORMATION:
I did a little backtracking and found the part number of the alternator voltage regulator I used to replace the old original bus regulator- it is F540XHD. It is a heavy duty replacement for the ubiquitous Motorcraft/Ford electronic regulator. You can find them for around $30 shipped (eBay using search descriptions) up to about $50. There are several ways to wire them, but I wired mine as simply as possible- connect the “A” terminal directly to the battery you are charging, connect the “S” terminal to switched 12V (switched on when your engine run switch is on), connect the “F” terminal to the field winding of your alternator (probably labeled “F”), and leave the “I” terminal disconnected. The metal case of the regulator connects to a good ground. This new regulator has a 30-amp field winding output capability, while the Detroit Diesel alternator uses less than 10 amps for its field winding, so this new setup should give you trouble-free operation for a long time, as it has for me. My starter batteries are now going on 11 years with the new regulator and they still start the engine like they did when they were new.
So far it seems that we can run the roof AC and charge the batteries simultaneously much better now. But fortunately for us, we haven’t actually needed much underway AC the past few months since we’ve made the changeover.
You are putting together an interesting electrical setup for your bus – I am eager to hear how it works out.
One thing does give me concern is you saying that you are using a “cheaper brute-force inverter to run the roof AC directly”. I hope you are using a pure sine inverter — the compressor motors in air conditioning units don’t like to run off modified sine and you may be shortening their life dramatically. We do like the flexibility of running our roof AC’s off battery that our current setup gives us – will you be able to do this at all?
Thanks for the info on the voltage regulator – I am sure I will find that very useful when I get back around to tackling that project.
Cheers,
– Chris
Ken Bolensays
Truely enjoy all of your posts. Especially enjoyed these on the lithium system. I am also looking to go off grid with my Motorhome. Have you every looked at Qunta Magnetics web site or there utube videos. They have small experimental motor/generators that I think would be ideal for motorhomes. If you ever get a chance, take a look at them. I would love to hear your opinion of their work. I have been a marine electrician for over thirty years and I have built many a large yacht and know about the weight of large AGM batteries. I know I don’t to be hauling them around in my RV. Thanks guys for all that you do.
This is some incredibly practical information. I always figured somebody was doing this, but I didn’t know who it was! I know that lithium batteries have absolutely transformed e bikes over the past five years. I have an ebike with 600 wh of LiFePo chemistry. It’s rated by the manufacturer for 2,000 cycles but it’s not a warranty. It’s an amazing pack, giving me 30 miles of riding with little assist from me. The e bike definitely cemented my view that efficiency is most important. This is a nickel’s worth of power to go 30 miles, or the output from a 100 watt solar panel for a day or so.
The air conditioning goal doesn’t seem completely out of reach. With grid tie panels, high wattage, selling for a dollar a watt, the raw power to run a single A/C is not that expensive. If you need a 3,000 watt generator, the good ones run are not cheap, and they are truly annoying to deal with. I’d hate to spend too much effort, right now, mounting 4kw of solar and building 15 kwh of storage, to run an air conditioner. Most people simply heat with propane. The solar dealer in Tucson I knew bought a small RV A/C from me, and he planned to mount it in a small room within his bus conversion. It would run off his battery bank, and this was ’87.
I’m not sure if the battery banks you use are based on the little cells that are used in everything from the Tesla to a laptop. In any event, a huge factory to build lithium cells can’t hurt the overall economics, especially of battery transport. I read stuff all the time about the ‘big breakthrough’ in Lithium, but it’s not happening yet. It’s not that hard to imagine that a low cost pack for an automobile will exist in ten years, and certainly the RV packs will simply follow in that wake.
I think it’s exciting to read what you have done, since anyone with a few hours can probably figure out roughly how it all works. Finding things seems to be remarkably challenging. I was a little shocked it was that hard to do this. Who knows. It’s worked for several years now. You might have done it right the first time. I’m extremely impressed and I definitely will aim toward making my golf cart batteries work until things settle out a bit.
Just as an aside, they really don’t make it easy, these days, to go with 12v off a battery. The first time I hooked up a meter to my new trailer, I was shocked to see a constant draw of about an amp. I finally traced it to the Dometic fridge, with a little computer. Gee, I started when they were just mechanical systems, and the 20 odd amp hours Dometic had claimed for itself, every day, was a big chunk of the single Group 24 battery included. So you end up working around the systems you buy with an RV. I only want a month in the sun in the winter, so I keep it very basic.
In some ways, you have a huge advantage with that bus. You can work it about the way you want it. I hope you find a way to mount some solar and keep that great old bus intact. Maybe one crisp
line of panels somewhere? Maybe a little paint on the side, or a trim piece?
Air conditioning on an RV via solar isn’t completely out of reach, but it IS a pretty far reach – especially if it forces you to park in the sun to even power the AC. But there are some people managing it, and I love that they are.
What is the feasibility of having the EMS start the generator automatically to recharge the battery when the low voltage alarm is triggered? What mechanisms might be employed to accomplish this?
We don’t have a generator auto-start control module, but I expect that many of them would be able to take a signal from the EMS as a start trigger. I do know that the Victron inverter has some nifty programmable features that can be set up to trigger a generator start on a range of input conditions too.
Great write up on the batteries, I built a 7 x 18′ solar cargo trailer with 2100 watts solar the goal being to run a 5,000 btu window AC to cool the trailer. I can get 70 deg in full sun at 100+ deg.
The problem is the equipment makes lots of heat going from solar to charge controller to battery back to inverter then to AC unit. I would say in the process I pick up 1500 to 2,000 btu heat. When I run the AC off a Honda 2000 or shore power it really kicks butt. With flooded batteries the system does not work to my satisfaction. I talked with elite power at the RV show but the guy there could not answer my questions as to how I could charge their batteries with my solar.
I can help you if you wanna plaster a million watts solar on your bus. I set mine up as actually 3 different systems, just in case something did not work I would always have some solar. Now I guy put 3000 watts on a 24′ trailer so I may need to add on another 1,000 maybe 🙂 I can tell you panels laying flat on the roof need washing every week or so unless it rains a lot.
One question I have however is elite told me you can draw a load from the batteries like 50 amps while at the same time charging the batteries with 50 amp , let’s say from solar – therefore the net effect is ZERO ? Info I have read is that its best to not charge the batteries – while drawing a load becauses it confuses the BMS ? Do you have any experience along those lines ? That would be great if you can let me know.
I just checked out your page – wow! Over the top, indeed!
What panels and controller did you go with for your roof?
I’m right now deep into researching solar options, and hoping to get some magical sun power on top of our bus soon.
Oh – and I’ve never had any trouble with the BMS getting confused by charging and drawing a load at the same time. We are often in that state – running the roof AC off the batteries while also generating DC with the engine alternator.
You can run what ever load you want off your batteries while your charging them. The charger just sees that the power if flowing out- it doesn’t care if it’s all into the batteries or into running other equipment connected up to the batteries.
Scott Helmann
35 year Electronics Tech, with an Electrical Engineering Background and as an additional duty I manage a large battery shop at a maintenance facility for the South Dakota Army National Guard
Hi guys, I am working on a lifopo4 set up for my conversion project with the plan to travel the world. I did buy a 12V airco system with a 12 V compressor with the understanding that the less you change from 12 v to 110 V the more efficient. My fridges is a 12 V marine compressor, the stove a 12 Volt/ diesel stove, hot water is a unit with heat exchange connected to the engine. I am thinking of installing a small solar panel to heat the water and of course a 450 – 500 amp solar array on the roof.
I came to the conclusion also to see if Victron can do the whole system.
One thing different i need is that I would like to have the option of 110 v and 220 v shore power for when we travel outside the US.
Did you ever sell your system?
Sounds like you are putting together a great system – but I definitely suggest consulting with an expert to make sure you put it all together right.
Keep in mind – there is indeed a significant loss going from 12V to 110V, but there is also a very large loss running high current 12V over longer wires. Since a roof air conditioner tends to be so far away from the batteries, the advantage of going with a 12V AC may be minimal.
We have not sold our battery back and upgraded to a larger setup yet.
After running on my LiFePO4 system for about 7 weeks, and giving a talk about them at the RTR, I’ve finially got my blog posting on them done: http://techno-viking.com/posts/lifepo4/
Tried calling Balqon; didn’t even answer the phone with a real person & not way to talk to anyone except leave a message for general corporate.
I did find on their site (like pulling teeth from a chicken) their BMS: https://www.technomadia.com/2012/09/a-year-on-lithium-rv-batteries/. The brochure takes a while to load. I found it under the tab “Support”. On the last page is a little schematic that gives notice they do know there are low voltage systems out there.
Their pages describing what the BMS does looks like it’s supposed to and does all the things, I think, we want. I’m still going to try to get a person on the line to discuss using 1 cell pack and their BMS.
I gave up on trying to find a low amp 12V air conditioner for my van. The ones developed are either mini-split or too large and designed for trucks. Some work off ice and cold water. Don’t think so.
So, I began a search for a HQ 120V thru-the-wall unit. I found Frigidaire models that will work. However, after converting AC to DC amps, it seems like am impossible goal to run one 8 hrs. The 2d no. is AC amps per hr, the 3rd, DC: 8,000, 8.0, 88; 9,800, 9.6, 108; 12,000, 11.1, 127. If I had a Balqon 700Ah cell pack, 80% is 560 usable Ah. Figure I need 100Ah for cooling, medical, cooking, etc. That leaves 460Ah for air conditioning. Divide by the 88, 108, or 127, depending on how many BTU’s you want, and you see it’s only 5:20 to 3:40. Of course, that’s with the A/C running full blast the whole time w/ no allowance for Energy Saver or Sleep mode switches. It also does not account for Ah going back in the bank if the sun’s out or if I drive the engine/alternator to town or somewhere.
EVEN IF I had the Ah storage (which I figured for the 9,800 BTU unit to require 1,100 Ah) I will have passed the balance point. IOW, I will not be able to recharge the bank. I only have room on a rack atop my Econoline 350 RB for 840W of panels, and I’d really rather do only 640.
Unless you suggest otherwise, I’m going to pursue the Balqon cell pack(s) and BMS and couple that w/ the Victron inverter/charger, solar controller, and monitor panel. Only your study of the Beta model literature you got will tell how well this plan will work.
Heating and cooling both take a relatively immense amount of power, as you’ve seen. It is really hard to build an off-grid system that can generate and store enough power for a full day’s air conditioning without needing to regularly rely on a generator.
It is a very tricky balancing act – and experimental. If you are having fun with this stuff – go for it, and keep sharing what works and what doesn’t.
But we absolutely can not make any specific endorsements or recommendations – we can only share our experiences.
Let us know if you try out the Balqon BMS – it looks interesting. There are several other generic BMS systems I’ve seen mentioned before while Googling around too, and I’ve even seen some people decide that for house battery use a BMS is actually potentially not needed since the cells tend not to drift out of balance.
There is no clearly defined “best” route agreed upon anywhere yet.
I am very eager to hear about your Balqon system. When you have stuff posted, be sure to come back here and link to it. I know there will be many interested!
JC Lewissays
I checked on Balqon. They sell replacement batteries for electric vehicles. That 700ah, single battery pack for $700 is EXTREMELY enticing.
It’s such a shame that Victron’s battery management module won’t work (so they say) on non-Victron-built battery packs. So, how can we “talk” to the Balqon? They don’t sell BMS’s. Do you think the Elite EMS would work? Then, there’s all the other p&p: temp monitors, fuses, etc.
I think the ideal system (today; next week’s newest products notwithstanding!) would be the Victron MultiPlus 3000W upgraded inverter, their MPPT solar controller w appropriate amperage size, the digital color monitor, a BMS that works w the Balqon battery pack, and all necessary p$p.
How can we find the “missing link” BMS? I’ll try calling Balqon next week and see if they know.
I called Victron in Maine today. Very nice people. It’s true, they have come out w/ an upgraded ver of their MultiPlus 3000 inverter/charger and it’s supposedly much more lithium friendly. It will work w/ anyone’s batteries and Batt Mgmt system (probably).
Also true they’re selling their own battery packs and management system. The later will NOT work w/ anyone else’s batteries.
Their lithium’s come pre-packaged in 60, 90, 160, and 200 Ah containers. They want them mounted w/terminals on top, not like AGM’s which can go anyway. All sounds very good EXCEPT their batteries must be the most expensive LiFePO4’s in the U.S. market.
I really don’t want to spend that much for batteries. However, I imagine using their matched set of batteries, inverter, and BCM should produce a finely-tuned system.
With a hoped-for 20% discount from a distributor, the batteries cost 60Ah $1,032; 90Ah $1,383; 130Ah $2,459; & 200Ah $3,074. Weights are 26.5, 35.4, 73, & 93 lbs.
The closest comparison to your 500Ah bank is3-160Ah (480) for $7,378 in a 27″ x 14″ footprint and 219 lbs. One can put 3-200Ah (600) together for $9,221 in a 33″ x 18″ footprint and 279 lbs.
Ouch, for sure. I’d like your comments on just how “too” expensive, if they are, are Victron’s batteries? Is the difference worth it to get their proprietary BCM and panels?
Great research! I had not seen any published prices on Victron’s lithium batteries yet – they have been “coming soon” for the past two years.
Are they actually available for order / shipping into the the US market now? I know one thing that has held back lithium in the US is the testing and certification requirements necessary to ship a pre-assembled battery. This is where a lot of the additional costs come in versus just buying cells and building your own battery from scratch.
Victron has actually sent us one of the new MultiPlus 3000’s with the improved lithium support to beta test, and I am going to see how well I can integrate it with the Elite EMS we already have. I’ve read the documentation on how to integrate a third-party EMS, and it looks pretty straightforward.
As for Victron’s battery prices…. That is indeed pretty high – but for someone who isn’t comfortable being an experimenter and building up a battery from cells, that is perhaps worth it for a fully supported, warrantied, and pre-integrated system.
After the Boeing battery problems I started wondering about fire risk with these batteries. Are the cell temps monitored? If a cell actually did catch fire can it be contained?
Your observation “…..during my last capacity drain test the Victron battery monitor indicated at one point that -280.6Ah had been consumed, but that a battery percentage remaining was 52%. I’m not sure how they can determine that a battery that has been 58% drained has 52% remaining — I am still hoping to get an answer from Victron support explaining this.”
I can answer this for you. I also use LiFePO4 cells and their a-hr capacity rating is very conservative compared to lead acid. A LA battery earns its a-hr rating based on an easy draw down over 20 hours to full depletion, whereas a LiFePO4 cell gets its a-hr rating in a brutal, 1 C discharge and only to 80% DOD. If a 500 a-hr LA battery was subjected to a 500 amp draw for an hour it wouldn’t make it because due to Puekert Effect would only have about 280 a-hr. The same 500 a-hr LiFePO4 would produce 500 amps for the entire hour and still have 20% remaining. When you draw less than 500 amps, the battery’s capacity is even higher.
I agree completely with your comments on the difference in how lead versus LFP batteries are tested, but that still doesn’t explain the discrepancy in the Victron user interface. It seems like a bug in the software to me.
Bob hit the nail on the head when he credited the Peukert Effect. To simply illustrate this with real numbers, a fully charged 225Ah T-105 battery can actually provide one ampere for 400 hours. Thus if only an ampere is drawn for 225 hours, the DoD is only 56%.
Dave Silvasays
Wow. A decade of reading the BNO and other RV forums and seeing the question “can i run my AC with an inverter?”, and the answer from some smart old guys “nope, can’t be done, not practical, to expensive”.
Anyway, have you looked into building your own monitoring and charging system with a Raspberry Pi? Someone above mentioned Arduino, but i think Rpi is more capable. Bedsides all the sensing, switching and managing you would need, it could send you a text to let you know how it’s going.
Thanks for some great info. Now it’s time for the two-year update (grin)
Sean and Louise at OurOdyssey have run their AC off of batteries for years – so there are examples on the bus boards of it being done. But indeed, very few people have gone and proved that it could be done practically.
As for custom monitoring with a Raspberry Pi or Arduino…. I love the idea, but so far haven’t had the time to even begin contemplating a hacking project like that. Maybe someday.
BTW – Victron has a new control panel system coming out this year that allows for remote monitoring and control which should give a lot of cool features in an off-the-shelf package.
And yep, a two year post is slated in the near future once I have some time to do some capacity tests. But the quick summary is that everything has been working great!
It occurs to me that a simple change in the pulley diameter on your bus’alternator would solve the problem. If engine rpm is at 1500, changing the alternator’s pulley to place it in an “overdrive” condition will spin it up to sufficiently compensate.
Sometimes when focusing on the electronics it’s easy to forget the mechanics that creates them.
This is a good thought, but our alternator is gear driven directly off of the engine and I don’t think there is any way to adjust the ratios to make it spin faster. Thanks for the idea though!
Hey there, I’m a fulltime RV boondocker who also recently took the leap to LiFePO4 with good results.
Last January, I acquired 260Ah (at 13.3V) of some 2 y/o ThunderSky batteries on clearance for about $850 delivered, which is comparable to the cost of some good new AGMs (but weigh 100lb less). The cells have no balancing circuit, yet have remained within 20mV of each other for four months now.
I use a $25 Arduino-like microcontroller to handle charging as well as high/low voltage disconnect on a per-cell basis. My charging scheme is solar only. I count amp-hours removed and the MC puts the same back in, plus a little more to account for coulombic efficiency of around 90%. I try to maintain the bank between 60-80% SoC because my #1 goal is to see if I can 7-10 years out of my LiFePO4s.
Thanks for stopping in – always a pleasure to encounter others playing around with this stuff. We are too hoping to get a similar life out of our bank. Here’s to the future!
Depends – what voltage does your alternator and solar put out, what are you storing in your battery and what do you need to run you house systems? More than likely your power system is 12v or 24v, and your house system will need 110. For that, you will be highly dependent on an inverter – get the best you can afford. Unless you can run everything off 12v/24v.
Switching the mobile palace completely over to 24v might be more of a project than you want to take on. During a complete tear down and rebuild of the bus it would be much easier. The little things start to be quite the problem: Wiper motors, instrument lamps, relays, pumps (got air bags?)fans and all other manner of annoying little things that you won’t find until they burn out. I’m sure if you took a critical look under the dash, you would shudder. Why not think along the lines of having a separate “house” system and vehicle system. If you are contemplating adding an additional pulley driven alternator, why not designate that for 12v vehicle systems and use the current gear driven alternator modified for 24v service or vice versa? This will save a load of money, time and aggravation in modifying items. You can also remove connections between the engine batteries and the house batteries to avoid discharging the batteries that start the engine.
I always try to anticipate failures and formulate solutions in advance and while a 24v custom starter is not difficult to do, it takes time and getting a replacement when you’re camped out on the playa for The Burning Man, waiting for a custom part is not ideal. Tow service off of the desert is available, but the towing companies that will do it charge for “off road” service at many times the usual rate. For a bus……. ouch. The more of the bus system you can leave stock, the easier it will be to find replacement parts in stock when you need them.
You might even consider going to a 48v battery system. The higher the DC voltage, the better the efficiency of the inverter providing AC power. Smaller wires and connectors are always welcome.
Thank you for all of your information. It’s one thing to talk about theory, but your hands-on experience is indispensable. I have been contemplating selling off my accumulated junk, packing up the cameras and the cat and doing the mobile thing myself. I glad that Karen Willmore sent me a link to your site.
There are a lot of advantages to switching to a 24V house system, but as you pointed out – there are a lot of headaches too.
Certainly the smart way is to go with a hybrid 12V / 24V system to avoid needing to replace any of the old under-dash system, but even then it is still tricky.
I was briefly tempted to go 24V, but the reason we did not was it was just too big of a project to take on retrofitting. Maybe someday if we ever decide we need a bigger inverter, then it would be worth it. Our current inverter is just about as large as you can get on 12V, and having smaller wires and less wire loss would be great.
BTW – getting 24V alternators and starters is not such a big challenge, most buses built more recently than ours (1961) are actually 24V native.
And if we were to ever break down, I can’t imagine a better place to have mechanical issues than at Burning Man. There is more engineering ingenuity out there on that desert for that week than you would find just about anywhere else short of NASA.
Hey Chris,
Sweet article!! I definitely appreciate you sharing your power systems design findings! I’m aspiring to install a system much like yours. Though, my wife has some “reservations” about the idea of letting me design and install it. Totally unfounded concerns of course! 😉 Anyway, you mentioned the folks at elitepowersolutions.com a couple of times.. Would you recommend that I go to them to design a system for my RV? Your other article about power boosting really makes a lot of sense too. A must have for me.. Think they’ll be able to tie all that in as well?
In addition, my wife and I are slowly pulling the trigger on going full-time. The hammer is about to drop! Got an offer on the house yesterday.. Cheers!!!
The folks at Elite Power Solutions have been a great resource for battery information and cells and how to protect things with a BMS, but they are not going to be able to do much to help you design your overall RV system – that isn’t their area of focus. They don’t do installation or design work, they are just the US importer of one particular brand of LiFePO4 cells.
But – they are very worth a call / email. Tell them we said hi!
If you look back on the post Chris did on the ‘Cost Analysis’ (linked above) – we listed all of the vendors we had checked out. Might be worth checking in with some of the folks doing RV systems to see what they’re up to these days since we first poked them. As we’ve not used any of them, can’t make any specific recommendations.
Troy Robertsonsays
I was wondering if you have anymore info on charging with solar panels and if there is a recommended charger for lipo4 with solar
Hi Troy – Chris has started some research on approaching our solar install, but we haven’t yet started the project. When we do, you can be sure we’ll blog about it.
Have you considered just setting the Absorb voltage on the
Victron to be equal to the Float voltage and skipping the Absorb step entirely? You would get a complete recharge during the Bulk phase, and then go straight into Float, allowing an automatic sensor output from the Victron to shut off your generator?
You might have also play with the End Amps setting for Absorb if Victron has one. Even if you cannot set a zero Absorb time, setting a very high value for End Amps should still cut off the Absorb part of the cycle. If it does not, that is a failing in the Victron. I am pretty sure you can use that strategy with a Midnight Solar charge controller.
To keep the batteries healthy long term, I float them at a lower voltage than is ideal for charging – so I think setting the absorption to be equal to float would result in a slower charge not taking full advantage of our battery capacity.
I’m not sure if any tweaks may be possible with playing around with the “End Amps” setting – I don’t remember seeing anything like this configurable in the Victron control panel, but next time I am playing around I’ll take a closer look.
I’ve heard good things about Midnight Solar charge controllers. Do you hove one? How do you like it?
Love the info on the battery system – but one assumption I think is key – number of useful cycles. Having lived with laptops for 10 years – I would say typical lifespan is about 500 discharges, certainly not 1000’s. I’ve never had a lithium battery last (keep more than 50% of original capacity) more than two years with daily use. Thoughts?
The chemistry in laptop batteries is a bit different, and the use case they are optimized for is vastly different than the types of batteries you would use in an RV house system. Laptop batteries are engineered for maximum capacity and for being drained to zero regularly – not for a maximum number of lifetime cycles.
On the other hand, RV house batteries (even lithiums) should never be drained 100% – and this makes a huge difference in enabling many more lifetime cycles.
Also – I’ve noticed that the new Mac laptops that do not have removable batteries have done more work to engineer for more cycles. Apple now rates their batteries at 1,000 full discharge cycles before capacity is diminished to 80%. For most people, that means the battery will outlast the useful life of the laptop.
Guys, thanks for the kind words and for spreading the lithium ion information. I can’t believe it’s been a year already since you were here. The software update is here waiting next time you come through Phoenix.
Thankyou for posting your results on your Lithium batteries so far. I would like to get rid of most of the 1000 lbs (1700 amps L16HC) of batteries we have to carry around but it doesn’t look like it will happen anytime soon. I too am a Technomad so I need electricity. We have 1580 watts on the roof. It does spoil the looks of the bus a bit but thats life. With that much shade we have never had the need for AC. We will be leaving Oregon in a couple of weeks to head south for our annual trip to Mexico. I can’t wait to get on the road again.
Jerry
I am in the middle of designing a upgraded RV for our family. All dry camping in very remote areas with terrible roads. Weight is a major issue and I have been considering Lithium given that the electric car industry is starting to make it affordable.
As a ground up design it looks like a cost break even to go with 24V using a second 24V alternator and solar. I have found better performance 24V air conditioners, many Sharp LCD’s use 24V, 24V LED lighting, water pumps, macerators, refrigerators, fans, etc. are available.
In your situation (lots of legacy 12V) you may consider (for items that can be isolated from ground) simply running 2 units in series to make a conversion to 24V most cost effective. It does seem that I may be able to use a 24V air conditioner (check out http://rencoolusa.com/dc-products/split-unit-air-conditioner/) using solar and battery alone. Prudence does include the use of a honda eu1000 (900W AC at 26lbs) as a backup for bad solar luck. There are several other options driven by new rules that you can not idle your truck at rest stops. Most trucks use 24V.
Indeed there are more options for DC cooling once you go up to 24V from 12V.
But no matter what, it will take a LOT of solar and a big battery bank to be able to get much air conditioner run time. How big of a solar install are you planning?
The little Honda generator will probably not be able to keep up with even a small air conditioner either.
I’m eager to hear more about your project, and thanks for the great lead on another DC AC option.
OK
Now you’ve made me write some things down.
A little background. We are a family of four that enjoy kayaking, mountain biking, hiking and motorcycles. We have been getting out every other week end for over 20 years. Currently using a long wheelbase extended chevy van with 2 T105 batteries (alternator charged), 3cu ft 12V fridge, Fantstic fan, water tank, sink microwave, sleeps 4, kayaks on top, one motorcycle in front, another in the back with the mountain bikes. Can’t recall ever staying in a location with power.
Stepping up (while the kids step out) to a long wheelbase, extending body high roof sprinter van and adding air conditioning, solar panels, shower and toilet to the above list while removing a 2 person sleeping area. Vehicle purchase is planned for the summer of 2013.
I agree with everything you wrote but we may be in very different situations. Check out this site http://www.moorepage.net/heatloss.html . The very simple (and only good enough for an estimate) spreadsheet helps you understand the problem. For us:
Heat gain calculator Gain, in BTU/hr = (surface area / R) * temp diff
BTU / hour â—Š Infiltration = cu. Ft. * R * air changes/hr * temp. diff
Inside temp = 72 Outside T 105
Element ft^2 R °F diff BTU Gain
” Lighting Watts 100 341
” People 2 682
Total insides 1,023
Floor 132 7 33 622
Ceiling 132 9 53 777
N wall 132 7 33 622
S wall 132 7 33 622
W wall 36 7 33 170
E wall 36 7 33 170
Windows 5 1 33 165
â—Š Infiltration, area 792 0.018 33 141
0.30
Total, outsides 3,290
Total, ins + outs 4,313 BTU
So this large van (with 2″ of foam wall insulation, shielded windows, canopy shade on sun side, minimal internal heating) should only take about 4300 BTU to cool. Other estimates are roughly the same.
Check out http://feddersusa.com/AZ7R05F2A.html#tab2 where 485W provides 5200 BTU. Verified here http://www.wind-sun.com/ForumVB/showthread.php?16201-Fedders-5000-BTU-A-C-test .
I add two large Sunpower high efficiency panels at 320W each, small 900W gen to fill in holes, run the van for 10 minutes in the evening to pre-cool, use 120 AHr 24V lithium to control weight.
So I built a little spreadsheet to see if this could work. The AC always runs from battery, the generator, or alternator, or solar simply charge or share the load.
12 to 4 4 to 8 8 to 12 12 to 4 4 to 8 8 to 12
Activity net watts sleep sleep wake out out dinner
net load w/hr 221 221 229 65 201
in 4 hrs 885 885 915 258 804 1496
Air temp 85 85 90 100 100 90
Sun angle to panel, ave 0 6 38 77 38 6
Panel x 2 320 0 66 384 597 377 65
Gen, minute 120 0 0 0 0 0 100
Alt, minute 2000 0 0 0 0 0 15
Generator, W 0 0 0 0 0 200
Alternator, W 0 0 0 0 0 500
Battery, 24 2880 1460 839 1462 3590 3584 2345
120 max % depletion 0.70
A hr
The day is broken in to 6 4 hour blocks. In the first group the % on time for each load is shown. The next group is the associated load in W-Hrs. I assume 14 hrs of sun with output reduced at low sun angle. The bold line (Battery) shows the remaining charge at the end of each 4 hour period with the loads and sources as shown. Anything over 2880 is not used but shown to indicate available power (may be good to simply run the AC for a while as apposed to the fan that is just intended to get the internal temperature the same as the outside temperature while we are ”out”.
Still need to run the van for 15 minutes to pre-cool the cabin and run the generator for about 100 minutes during high load at dinner (cooling, TV, laptops, Sat.). I would let the internal temp rise until the AC duty cycle is 40% while sleeping.
So this is the concept. The AC is 115V so I added 10% loss for the inverter. With no idle truck rules, some new DC compressor products and continued growth in off grid solar I would expect a DC unit that would match the Fedder performance shortly.
For our little van, I think it is just do-able. A whole bus may be a different story but with insulation, window removal and lots of panels on the roof …….. maybe.
Currently all just paper and hot air but seems there may be a successful path.
Ron
Sorry about the table formatting. Let me know if you would like me to try the tables in a different format.
Tom Phillipssays
Hi Chris,
My goofy dogs had to go outside so I checked email (3am) and saw your message.
The starter is the easy part. A 24v one from a gm 4905 will drop in. Its fed by a relay so its contact supply could be changed to 24v.
Ditto for the alternator/regulator mechanically.
The big 12v bus loads I can think of are:
1) The heat/cool system
2) two big 12v contactors for general/reading light loads
3) original bus bathroom blower/pump
4) the defroster blowers.
The defroster can be changed to 24v (relay driven too).
If your conversion dispensed with 1,2 and 3 then bus wise I think its practical since remaining loads are lights, instruments and a few engine control air solenoids.
There are a few other details like the bus alternator power with has it own contact in the master switch(good) and there is a special alternator relay that indicates alternator is running that may have to be swapped.
The maintenance manual has great electrical diagrams. I may have the alternator diagram for a 4905 somewhere for reference.
Hi Guys, Thanks so much for detailing your progress. Neat to see convergence between RV systems and off grid solar/wind technology where generators are used more and more as backup power. This is definitely the future. Have you considered switching to the 24volt version of the bus alternator? Its rated at 225amps which is about 3kw, enough to comfortably support one of the modern minisplit units. Figuring out how to merge the 12volt bus electrics would be a challenge (ie, fun) of course.
I’ve often daydreamed about what it would take to go to a 24V system. We could get a more powerful alternator, wouldn’t need such hefty battery cables, and the 24V version of our Victron inverter actually would be able to charge the batteries faster too.
I haven’t heard of anyone converting a 4106 to use 24V, but I imagine it can be done. But I’m not sure if it can be done in a cost-effective way to make the project worthwhile.
I wonder what it would take to change to a 24V starter motor?
The rest of the 12V loads could be driven via a DC-to-DC converter I think.
Anyway – if you have any advice or leads on how to make this possible, I’m sure some others reading this would love to know more! As you said, this stuff is fun… 🙂
Thanks for the write up, guys. Greatly appreciated. I’ve factored in LiFePO4 as a possible battery solution in my rig.
Questions:
– What are the dimensions (length, width, height) of your battery pack?
– If you don’t live full time year round (for example, 6 months on and 6 months off), would you still have invested in LiFePO4?
And for the second question, that’s far too hypothetical of a scenario for us to answer. But considering one of our primary goals has been to play with cutting edge stuff – probably. But us not living full time on the road is something that’s not even a consideration for us.
Hello Chris I’m sending this comment from Northerner Mexico in Chihuahua. Me and my uncle run a large Pecan Nut farm and move back and forth to take care of it. We are vary interested in putting a large Lithium battery bank in are RV and we already run are home on Solar Power so we want to run are RV on solar too! Do you have e-mail that we could contact you on for more ideas.
Great article! If you are looking for a higher output from your engine alternator, Put a smaller diameter pulley in place of the one on the alternator now. They are quite inexpensive and can be found at auto parts and truck parts suppliers. Do keep the alternator’s speed within the manufacturer’s spec’s. Most alternator manufacturers have on-line information and formulas for calculationg your required amps output at whatever engine rpm you want to run at.
The only problem I would see for using a single cell ballancer for multiple cells in parrallel is having it draw enough current to ballance when charging.
One question I have is how the wires are connected to the battery. With four screws rather than a large bolt, standard crimp connectors won’t work.
Indeed, ideally the balancers would be able to put a larger balancing load, and we could actually add multiple passive balancers to each of the cells in parallel to accomplish this.
Elite sells these passive balancers for just $9.
Our normal charge voltage doesn’t push the cells to the balancing point, so it isn’t an issue. When I want to balance – I set the Victron to a very very low charge current so that I don’t overwhelm the single balancing shunt.
As for connecting the battery cables – Elite provided screw on ends that we crimped to the cables. I used two positive and two negative wires in parallel to handle the load since #0000 wire wasn’t available, nor could I figure a way to attach a #0000 wire to the battery with these connectors even if I had found some when I needed it.
thanks for this awesome report. I looked forward to this for quite some time, since I followed all your last posts on this technology.
I am in the planning phase for such a system myself (also with Victron), but with Winston batteries in my case. Two things intrigue me the most:
1.) How do you prevent over-charging from the Victron or the engine alternator? The Victron shuts itself off at 14.2V, as you say – but what happens in non-perfectly balanced state, when one cell is above 3.8V and a power cut-off is initiated? Or when the alternator continuously charges, and the EMS shuts off? In this case you cut off the connection to the Victron (because battery is disconnected), but you lose AC and Inverter functionality as well?
2.) I just realized with this post, that you only have four balancer and sensor boards. This means, that the packs of five cells (each forming 500AH 3.2V) are not balanced inside? As far as my tests go, this is OK with starter applications (short, hard drawal of power, but directly afterwards charging the pack), but not with deep-cycle applications? In deep cycle, the individual cells tend to drift away from each other, resulting in a potential damage because of under/over voltage. I am just interested whether you measured individual cells as well… I would bet after one year, that the individual cells inside a 5pack are already not balanced anymore. (This was the case in my testing, at least…)
That´s why I tested with up to 16 individual balancer boards (4x(4x100AH)), each with separate cutoff for high voltage protection and low voltage protection. The only problem I have is the fabulous Victron – when I cut connection because of over voltage protection during charging, the inverter stops working. Currently we investigate in switching off the internal charger with VE.Configure, so that the inverter/power assist/power shave still works.
I enjoy reading your posts! Keep up the good work…
It looks like you have done some awesome research of your own – I’d love to compare notes. Have you blogged about your project anywhere?
In answer to your questions:
1) I’ve played around with different configurations of the contactors. At first we were intending to use a battery isolator (diode style) wired up with the contactors so that the battery could still be charged when the LV alarm is triggered, and discharged when the OV alarm is triggered. This would have been pretty foolproof, but would have required a huge and expensive battery isolator to handle the current demands, and in the end I’ve found that this was needlessly complex. In theory – the alarms being triggered should be a rare occurrence, and that has proven so far to be the case.
Especially since the cells seem to have no problem staying balanced over time.
The one place the OV alarm risks getting easily triggered now is when charging off the alternator (though I think I might be able to regulate the alternator peak charge voltage down) – but when that trigger happens in my tests the inverter is still able to be powered by the bus alternator and starting battery which are still in the circuit and in my testing it has worked well. But I try to avoid this situation by turning off the bridge when the battery is near 100% unless we are running the roof AC all out. I’d rather reach a destination with the battery at 80% than keep the batteries constantly bouncing into the OV alarms while charging at 100%.
2) The 5x100Ah 3.2V combined cells are wired in parallel (with 100A fuses as bridges in case a cell shorts so it can’t harm its neighbors) so that they are always balanced with each other and thus need only one sense board for the bunch. This was how Elite Power Solutions instructed us to wire the battery, and in this configuration they told us that other balancing/sense boards would be redundant.
To test the individual sub-cells to confirm balance, I suppose I would have to dismantle all the cross-connects on the battery bank. Do you really think that is a concern? Elite was convinced it would not be, and with cells wired in parallel I can’t understand how a cell could ever get out of balance.
What sort of results have you seen?
As for hacking the Victron – let me know if you figure out a way to control the charger in response to a trigger. I know the newest models from Victron have a new control port designed to interface with their own lithium batteries – have you looked into this yet?
One other question for you – why Winston batteries? Can you share some more about your own research into picking a cell provider?
interesting how try and error on different continents goes the same way. So far, I did not put my findings on the web – I wanted to test this out for myself at first, afterwards going public with it. Furthermore, if you are experimenting with this technology, there is virtually no one you can talk to about it, few even know there is this technology. This is strange, when you take into account that in Europe you have a severe weight problem – trailers are only allowed up to 3.5tons, and the average RV stays below 5tons. Lithium is a perfect choice for these vehicles – not talking about all the other advantages these batteries have. The main thing over here is getting the charging/discharging foolproof – this is not ready for the market yet (if you exclude the USD6000 Victron/Mastervolt products).
I experimented with diodes as well, but put then aside because of cost and voltage drop issues. I am now using MOSFET switches instead – minimum voltage drop, minimum power usage, switching capacity (right now) up to 260A / 12V. With these, I can switch off DC-DC Charger, Solar and AC-DC chargers in case of over voltage, as well as switch off all 12V devices (Inverter) in case of under voltage.
Interesting is the cell balance issue. I am happy to hear that you have no problem with this so far – what intrigues me is if this would be the case if you would have deep cycled your pack more. How many cycles does the Blue Power Panel read out? I read in a few posts of you that you were not boondocking that much… Perhaps this is why.
The advice from your reseller is a little bit odd, to say the least. Every battery suffers from cell variances. Every lithium as well as every lead-acid. And if you hear around your fellow bus addicts, if they change their battery pack it´s because of one battery out of the pack gone bad, while others are not new, but still usable. And even this defect battery is perhaps usable in theory, but one of the six cells inside has gone bad, making the whole battery (and in consequence the whole pack) unusable.
While these variances are absolutely tolerable for quite a long time in lead-acid batteries, you get lots of problems with this in lithium configurations, because lithium goes bad from ONE over/undercharge, while lead-acid is quite tolerant against this mishandling. This is why you don´t balance lead-acid batteries – because they can cope with it for quite a long time. Lithium can´t. Since every cell is a little bit different, it behaves a little differently during charge and discharge.
Theoretically, every cell in a row SHOULD balance itself with and against its neighbors by varying its internal resistance depending on state of health and therefore absorbing/giving more or less power during charge than it´s neighbors, balancing themselves over the rail they are connected with. But bevause of slight variances and drifts, eventually (especially in high load situations) these cells are in a situation where one single cell in the rail is running into over/under voltage and dies.
That´s why usually every cell is being balanced – at least in the configurations I know of. {Perhaps this is typical german over-engineering – if so, please let me know ;)}
All of this only applies to deep cycle situations – if you don´t deep cycle, you can get away without balancing. A european university made a test with a winston battery cycling 10% of the capacity with 1C. After 13.000 (!) cycles they stopped the test, because there was virtually no wear down in the cell detectable.
This (sort of) answers your question why I use winston batteries – they are available, you get single cells of significant capacity if you like, and the above test of the university is very impressive. Furthermore, you can charge them without a heater at down to -40 degrees C. No thermal runaway, no risk of fire or explosion – they were just a sensible choice to make. So far, I have no bad things to say about them.
The charger part of the multiplus cannot be switched by a trigger, as victron told me.
The lithium system from Victron is connected to the Lynx System with four modules, which interfaces to the bus system of the multiplus. There is a separate interface doing all the necessary calculations and switching batteries and multiplus on and off.
What a great report Chris….exhaustive, and complete. You are on the cutting edge of the Lithium Ion battery frontier, and we appreciate the work, research, and long term experience you are going through that will benefit all of us who are looking to this battery technology to make our Technomad travels more flexible and fulfilling!
I’ve been waiting for this report. Thank you , thank you for testing it, figuring it out and telling us how it does in the real world. Terrific write up. I really hope the industry starts tailoring these for the RV world.
I think one of the biggest advantages of your system is that you can use 80% of the battery capacity. It’s like adding a whole additional lead-acid battery but in a smaller foot print and much less weight. In an RV, that is huge! Well, even better because you don’t lose power as the battery depletes like in a lead-acid.
One other thing, I am interested in is how to handle cold weather charging, tho I suppose you just avoid it altogether.
We’ve heard of folks who keep an electric blanket or space heater in their battery bay to warm their LFP up before charging. Which if we found ourselves needing to charge in very cold weather is what we’d try. But considering we have no heating system for the bus, that’s an unlikely scenario for now 🙂
According to Elite Power Solutions, the official temperature rating for our cells is -20 to 65 C or -4 to 149 F.
That is a pretty wide range that should cover most every situation we encounter.
They did recommend not charging the batteries quickly though until they have warmed up above freezing, and this is where I’ve heard of battery heating blankets sometimes used.
Great post, we really enjoy watching your adventure into lithium. When it is all sorted out I’m sure us late adopters will dive in. Would you be willing to share how you bridged your coach alternator to your house bank? We have the same coach side set up, our battery bank consists of 6 4D AGMs with a Magnum Inverter. Running the AC off the engine alternator would be a really great upgrade.
Our LFP batteries are in the bay that the bus used to use for the AC blower chamber when it was a seated passenger coach. There was an already existing heavy gauge DC power cable that runs from this chamber essentially straight back to the alternator.
I used the high current Tyco contactor, wired up to a switch to let me control whether or not the bus house system is bridged to this cable and tied into the bus alternator and starter battery.
It is pretty simple, actually.
Eventually I want to put a smart switch in that automatically disconnects when the bus engine stops so that I never accidentally drain the bus starting batteries while camped.
Loved the tech post, very well laid out and understandable. One more reason I enjoy your blog, it feeds my techie side on the newest ideas for RV life. :c)
Great write up Chris. Could you list a “What’s in the Bag” for us, like listing all the components and their initial costs, so we get an idea of just how much we’d be looking at cost wise to do what you’ve done?
Our current charge settings are bulk / absorption charge to 14.2V, absorb for 1 hour (we can’t lower this), and then float at 13.6V. We have temperature compensation, equalization, and battery “storage mode” features disabled as well.
These alarm wires were initially connected to two Tyco EV200 Contactors that could completely disconnect the battery in the event of an alarm situation, saving the battery from harm. I’ve now modified the system so that one contactor works as a battery disconnect wired up to the alarms, and the other can be triggered to bridge in current from the bus’s engine alternator to charge our batteries and/or run a roof AC while we are underway.
Chris I have a perplexing inverter issue that I hope you can shed some linght on. My Oliver Legacy Elite II came from the factory with 320 watts of solar, four Trojan T105 batteries, and a 2000 watt Xantrex inverter. The inverter shuts down at eleven volts even though the batteries still have over 80% amp hours left. When the inverter shuts off the battery volrage will immediately jump to over 12. Start the inverter again and the same thing happens. I took the batteries to a Trojan master distributer who put them on a load device overnight and the batteries are perfect.
Any ideas?
Contacting Oliver for support of the system you paid them to install is your best bet. We haven’t run lead acid since our own Oliver days, as evidenced by the very post about Lithium you’re commenting on 🙂
Have you ever hear of converting a chest freezer into a refrigerator. Have not attempt. But its one of many ideas for my 58 4104.
I’ve heard of conversion kits to do this – but have never researched them. In yacht building, a lot of times custom shaped freezers are built to fit the shape of the hull – maybe you can check for further resources there. That might be a great idea for a bus conversion starting from scratch.
– Chris
I don’t remember to do it all the time but it is a really good idea to to take your rings off when working with electricity, even a top quality gold ring can get pretty damn hot if it gets enough current through it..
Absolutely smart advice!
I almost always remember to take my ring off – the trick is remembering where I put it when I go to put it back on. *grin*
Don’t leave out necklaces that can dangle onto the terminals while you are working. It’s not a bad idea to tape the shank of screwdrivers so they aren’t long metal sticks. The same goes for any wrenches that are long enough to short terminals if they slip out of your hand while you’re working around (not even just on) the battery pack.
Chris, have you hooked your lithiums to the alternator for charging while driving? I have a 400 Ah lithium pack and am concerned about it burning the alternator out demanding too much – is that a real worry and if so, do you have a solution. I have a Sprinter van based rv (diesel) with a regulator built into the alternator.
Thanks, Joe
You will have to check into the specs on your alternator. Our heavy-duty bus alternator is designed to run at full-output non-stop, and is great for charging up our batteries underway. I’m not at all familiar with the setup in the Sprinter however.
Your power management box should be able to be programmed so you won’t exceed the capability of your alternator when charging. I think I remember reading that in the Victoreen spec sheet when I was doing some research last year. The cheapest option is charging up while you’re plugged into AC. Using diesel to recharge is expensive unless your schedule has you off the grid for a while. Even though you might think that it isn’t anything extra since the bus motor is so big, looked at in terms of kWh units, it’s expensive. If you will be paying for a slot with hookups, get your monies worth and top up the battery pack.
Obviously, if we know we are heading to a campground with electric, we don’t worry about it and just plug in when we get there. But we very frequently live off-grid for extended periods of time, and charging while underway inbetween boondocking locations is awesome and a very cost effective to top off the battery banks. Certainly much cheaper than running the diesel generator if the sun can’t keep up with our solar setup…. or paying for a generic and boring ‘RV Slot’ just to get an electric hook-up.
Hi Chris! Over the past 15 years I built out a 40-foot bus with a Detroit Diesel with the 270A gear driven alternator. I am also considering running my air conditioning using the bus alternator + inverter. Now, I think I know what may be causing your net battery drain when running your AC on inverter power with the bus alternator trying to keep up: your external voltage regulator sense wires need to go directly to your battery terminals. If your engine is like mine, it has a crappy old-school external voltage regulator the size of a shoe box with early TO-3 transistors. These old regulators go out of spec and require frequent adjustment. Get rid of it. I replaced mine with a modern external regulator designed for a fairly high-current field winding. It’s a pretty generic regulator I got for less than $20, and is rated for at least twice the field winding current of the bus alternator (which is not very much- I think about 8 amps). The new regulator is much smaller and rated for a 20+ amp field winding. It keeps the battery voltage constant at 14.1V charging voltage, and has never failed now going on 10 years and 20,000 miles. The important thing is that the regulator needs to sense the actual voltage of the battery it is trying to charge, not anywhere else in the system, as the high load current from your inverter (with air conditioner running) will cause a significant voltage drop through your cables that prevents your battery from getting charged properly. No matter how heavy gauge your cables are, you will always have a voltage drop when you draw that much current through them. What happens is the regulator thinks it’s keeping a battery at 14.1 volts but in fact, it is keeping some cable terminal or the alternator output at 14.1 volts while the battery voltage could be less than it needs to maintain charge. Connect the voltage regulator at the battery bank itself, and run the field output back to the engine alternator.
The voltage regulator is wired directly to the starter battery terminals – but the house lithium battery was formerly 25′ further forward and indeed, as expected, much of the loss was due to that long wire run.
I’ve more recently relocated the house batteries to be nearly adjacent to the starting batteries – and that has made a huge difference.
Replacing the 50 year old voltage regulator with a smarter and more modern design is on the todo list too. I’ll get around to that project one of these days.
I hadn’t realized how cheap modern replacements were – I might have to look into that sooner rather than later!
– Chris
Awesome. With the house batteries located next to the starter batteries can you now run your roof AC while driving and keep all batteries maintained too?
I’m planning to do things differently on my bus…
I’m going to install a second inverter at the bus alternator that will act like a second generator input in my system. The inverter is set up to turn itself on only when the engine is running, and turns itself off when the engine stops. This inverter will be sized large enough to run the roof AC as well as the house battery charging equipment that converts AC power into a DC charge profile. The output of this inverter goes into a relay-type automatic transfer switch just like you would have for a generator set.
When the engine turns off and the engine inverter switches off, the transfer switch enables a second inverter to power all the house alternating current needs with the exception of the roof AC and battery charging equipment. This second inverter is selected to be more efficient than the one connected to the engine alternator, because it runs off the house battery system and needs to conserve power. However, it does not need to produce as much output because it only runs the smaller house appliances.
A similar transfer switch relay is installed that allows shore power to override all other AC power inputs and also energize the roof AC and battery charger.
What I like about this system is that the house batteries get charged with the power converter charger and not directly off the engine alternator- I find that this set-up regulates the charge profile a lot more accurately and gets the batteries charged faster as well. Also, I am not relying on my house inverter to run the roof AC. I use a cheaper brute-force inverter to run the roof AC directly off the bus alternator current. Keeps the systems isolated too- I never have the starter batteries connected to the house batteries this way.
VOLTAGE REGULATOR INFORMATION:
I did a little backtracking and found the part number of the alternator voltage regulator I used to replace the old original bus regulator- it is F540XHD. It is a heavy duty replacement for the ubiquitous Motorcraft/Ford electronic regulator. You can find them for around $30 shipped (eBay using search descriptions) up to about $50. There are several ways to wire them, but I wired mine as simply as possible- connect the “A” terminal directly to the battery you are charging, connect the “S” terminal to switched 12V (switched on when your engine run switch is on), connect the “F” terminal to the field winding of your alternator (probably labeled “F”), and leave the “I” terminal disconnected. The metal case of the regulator connects to a good ground. This new regulator has a 30-amp field winding output capability, while the Detroit Diesel alternator uses less than 10 amps for its field winding, so this new setup should give you trouble-free operation for a long time, as it has for me. My starter batteries are now going on 11 years with the new regulator and they still start the engine like they did when they were new.
So far it seems that we can run the roof AC and charge the batteries simultaneously much better now. But fortunately for us, we haven’t actually needed much underway AC the past few months since we’ve made the changeover.
You are putting together an interesting electrical setup for your bus – I am eager to hear how it works out.
One thing does give me concern is you saying that you are using a “cheaper brute-force inverter to run the roof AC directly”. I hope you are using a pure sine inverter — the compressor motors in air conditioning units don’t like to run off modified sine and you may be shortening their life dramatically. We do like the flexibility of running our roof AC’s off battery that our current setup gives us – will you be able to do this at all?
Thanks for the info on the voltage regulator – I am sure I will find that very useful when I get back around to tackling that project.
Cheers,
– Chris
Truely enjoy all of your posts. Especially enjoyed these on the lithium system. I am also looking to go off grid with my Motorhome. Have you every looked at Qunta Magnetics web site or there utube videos. They have small experimental motor/generators that I think would be ideal for motorhomes. If you ever get a chance, take a look at them. I would love to hear your opinion of their work. I have been a marine electrician for over thirty years and I have built many a large yacht and know about the weight of large AGM batteries. I know I don’t to be hauling them around in my RV. Thanks guys for all that you do.
Hi Ken –
Quanta Magnetics comes off as a lot of smoke and mirror, but if you ever play with it and make it work to charge batteries in and RV do let us know.
– Chris
This is some incredibly practical information. I always figured somebody was doing this, but I didn’t know who it was! I know that lithium batteries have absolutely transformed e bikes over the past five years. I have an ebike with 600 wh of LiFePo chemistry. It’s rated by the manufacturer for 2,000 cycles but it’s not a warranty. It’s an amazing pack, giving me 30 miles of riding with little assist from me. The e bike definitely cemented my view that efficiency is most important. This is a nickel’s worth of power to go 30 miles, or the output from a 100 watt solar panel for a day or so.
The air conditioning goal doesn’t seem completely out of reach. With grid tie panels, high wattage, selling for a dollar a watt, the raw power to run a single A/C is not that expensive. If you need a 3,000 watt generator, the good ones run are not cheap, and they are truly annoying to deal with. I’d hate to spend too much effort, right now, mounting 4kw of solar and building 15 kwh of storage, to run an air conditioner. Most people simply heat with propane. The solar dealer in Tucson I knew bought a small RV A/C from me, and he planned to mount it in a small room within his bus conversion. It would run off his battery bank, and this was ’87.
I’m not sure if the battery banks you use are based on the little cells that are used in everything from the Tesla to a laptop. In any event, a huge factory to build lithium cells can’t hurt the overall economics, especially of battery transport. I read stuff all the time about the ‘big breakthrough’ in Lithium, but it’s not happening yet. It’s not that hard to imagine that a low cost pack for an automobile will exist in ten years, and certainly the RV packs will simply follow in that wake.
I think it’s exciting to read what you have done, since anyone with a few hours can probably figure out roughly how it all works. Finding things seems to be remarkably challenging. I was a little shocked it was that hard to do this. Who knows. It’s worked for several years now. You might have done it right the first time. I’m extremely impressed and I definitely will aim toward making my golf cart batteries work until things settle out a bit.
Just as an aside, they really don’t make it easy, these days, to go with 12v off a battery. The first time I hooked up a meter to my new trailer, I was shocked to see a constant draw of about an amp. I finally traced it to the Dometic fridge, with a little computer. Gee, I started when they were just mechanical systems, and the 20 odd amp hours Dometic had claimed for itself, every day, was a big chunk of the single Group 24 battery included. So you end up working around the systems you buy with an RV. I only want a month in the sun in the winter, so I keep it very basic.
In some ways, you have a huge advantage with that bus. You can work it about the way you want it. I hope you find a way to mount some solar and keep that great old bus intact. Maybe one crisp
line of panels somewhere? Maybe a little paint on the side, or a trim piece?
Battery stuff:
http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries
http://www.plugincars.com/tesla-roadster-battery-life-study-85-percent-after-100000-miles-127733.html
Air conditioning on an RV via solar isn’t completely out of reach, but it IS a pretty far reach – especially if it forces you to park in the sun to even power the AC. But there are some people managing it, and I love that they are.
Thanks for sharing the interesting links.
– Chris
What is the feasibility of having the EMS start the generator automatically to recharge the battery when the low voltage alarm is triggered? What mechanisms might be employed to accomplish this?
Great job on your site and thank you for sharing!
We don’t have a generator auto-start control module, but I expect that many of them would be able to take a signal from the EMS as a start trigger. I do know that the Victron inverter has some nifty programmable features that can be set up to trigger a generator start on a range of input conditions too.
Hi guys
Great write up on the batteries, I built a 7 x 18′ solar cargo trailer with 2100 watts solar the goal being to run a 5,000 btu window AC to cool the trailer. I can get 70 deg in full sun at 100+ deg.
The problem is the equipment makes lots of heat going from solar to charge controller to battery back to inverter then to AC unit. I would say in the process I pick up 1500 to 2,000 btu heat. When I run the AC off a Honda 2000 or shore power it really kicks butt. With flooded batteries the system does not work to my satisfaction. I talked with elite power at the RV show but the guy there could not answer my questions as to how I could charge their batteries with my solar.
I can help you if you wanna plaster a million watts solar on your bus. I set mine up as actually 3 different systems, just in case something did not work I would always have some solar. Now I guy put 3000 watts on a 24′ trailer so I may need to add on another 1,000 maybe 🙂 I can tell you panels laying flat on the roof need washing every week or so unless it rains a lot.
One question I have however is elite told me you can draw a load from the batteries like 50 amps while at the same time charging the batteries with 50 amp , let’s say from solar – therefore the net effect is ZERO ? Info I have read is that its best to not charge the batteries – while drawing a load becauses it confuses the BMS ? Do you have any experience along those lines ? That would be great if you can let me know.
Jerry
http://overthetopcargotrailer.blogspot.com/
Hi Jerry –
I just checked out your page – wow! Over the top, indeed!
What panels and controller did you go with for your roof?
I’m right now deep into researching solar options, and hoping to get some magical sun power on top of our bus soon.
Oh – and I’ve never had any trouble with the BMS getting confused by charging and drawing a load at the same time. We are often in that state – running the roof AC off the batteries while also generating DC with the engine alternator.
Where did you read that this was a bad idea?
Thanks for sharing a truly extreme setup!
– Chris
You can run what ever load you want off your batteries while your charging them. The charger just sees that the power if flowing out- it doesn’t care if it’s all into the batteries or into running other equipment connected up to the batteries.
Scott Helmann
35 year Electronics Tech, with an Electrical Engineering Background and as an additional duty I manage a large battery shop at a maintenance facility for the South Dakota Army National Guard
Hi guys, I am working on a lifopo4 set up for my conversion project with the plan to travel the world. I did buy a 12V airco system with a 12 V compressor with the understanding that the less you change from 12 v to 110 V the more efficient. My fridges is a 12 V marine compressor, the stove a 12 Volt/ diesel stove, hot water is a unit with heat exchange connected to the engine. I am thinking of installing a small solar panel to heat the water and of course a 450 – 500 amp solar array on the roof.
I came to the conclusion also to see if Victron can do the whole system.
One thing different i need is that I would like to have the option of 110 v and 220 v shore power for when we travel outside the US.
Did you ever sell your system?
Best regards Thijs
Sounds like you are putting together a great system – but I definitely suggest consulting with an expert to make sure you put it all together right.
Keep in mind – there is indeed a significant loss going from 12V to 110V, but there is also a very large loss running high current 12V over longer wires. Since a roof air conditioner tends to be so far away from the batteries, the advantage of going with a 12V AC may be minimal.
We have not sold our battery back and upgraded to a larger setup yet.
Cheers,
– Chris
After running on my LiFePO4 system for about 7 weeks, and giving a talk about them at the RTR, I’ve finially got my blog posting on them done: http://techno-viking.com/posts/lifepo4/
I’m very happy with them so far.
Tried calling Balqon; didn’t even answer the phone with a real person & not way to talk to anyone except leave a message for general corporate.
I did find on their site (like pulling teeth from a chicken) their BMS: https://www.technomadia.com/2012/09/a-year-on-lithium-rv-batteries/. The brochure takes a while to load. I found it under the tab “Support”. On the last page is a little schematic that gives notice they do know there are low voltage systems out there.
Their pages describing what the BMS does looks like it’s supposed to and does all the things, I think, we want. I’m still going to try to get a person on the line to discuss using 1 cell pack and their BMS.
I gave up on trying to find a low amp 12V air conditioner for my van. The ones developed are either mini-split or too large and designed for trucks. Some work off ice and cold water. Don’t think so.
So, I began a search for a HQ 120V thru-the-wall unit. I found Frigidaire models that will work. However, after converting AC to DC amps, it seems like am impossible goal to run one 8 hrs. The 2d no. is AC amps per hr, the 3rd, DC: 8,000, 8.0, 88; 9,800, 9.6, 108; 12,000, 11.1, 127. If I had a Balqon 700Ah cell pack, 80% is 560 usable Ah. Figure I need 100Ah for cooling, medical, cooking, etc. That leaves 460Ah for air conditioning. Divide by the 88, 108, or 127, depending on how many BTU’s you want, and you see it’s only 5:20 to 3:40. Of course, that’s with the A/C running full blast the whole time w/ no allowance for Energy Saver or Sleep mode switches. It also does not account for Ah going back in the bank if the sun’s out or if I drive the engine/alternator to town or somewhere.
EVEN IF I had the Ah storage (which I figured for the 9,800 BTU unit to require 1,100 Ah) I will have passed the balance point. IOW, I will not be able to recharge the bank. I only have room on a rack atop my Econoline 350 RB for 840W of panels, and I’d really rather do only 640.
Unless you suggest otherwise, I’m going to pursue the Balqon cell pack(s) and BMS and couple that w/ the Victron inverter/charger, solar controller, and monitor panel. Only your study of the Beta model literature you got will tell how well this plan will work.
Sorry, wrong link:
http://www.balqon.com/wp-content/uploads/2013/07/36_36bms_brochure_balqon.pdf
Do whatever you wish. We take absolutely,positively no responsibility for your decisions or actions.
Heating and cooling both take a relatively immense amount of power, as you’ve seen. It is really hard to build an off-grid system that can generate and store enough power for a full day’s air conditioning without needing to regularly rely on a generator.
It is a very tricky balancing act – and experimental. If you are having fun with this stuff – go for it, and keep sharing what works and what doesn’t.
But we absolutely can not make any specific endorsements or recommendations – we can only share our experiences.
Let us know if you try out the Balqon BMS – it looks interesting. There are several other generic BMS systems I’ve seen mentioned before while Googling around too, and I’ve even seen some people decide that for house battery use a BMS is actually potentially not needed since the cells tend not to drift out of balance.
There is no clearly defined “best” route agreed upon anywhere yet.
Good luck,
– Chris
You need four cells for a “12v” system. Are you planning on running a 3.2v system? I don’t think anyone would support that.
I’m working on a sytem with Balqon 260 Ah cells, I’ll blog about it when complete.
I am very eager to hear about your Balqon system. When you have stuff posted, be sure to come back here and link to it. I know there will be many interested!
I checked on Balqon. They sell replacement batteries for electric vehicles. That 700ah, single battery pack for $700 is EXTREMELY enticing.
It’s such a shame that Victron’s battery management module won’t work (so they say) on non-Victron-built battery packs. So, how can we “talk” to the Balqon? They don’t sell BMS’s. Do you think the Elite EMS would work? Then, there’s all the other p&p: temp monitors, fuses, etc.
I think the ideal system (today; next week’s newest products notwithstanding!) would be the Victron MultiPlus 3000W upgraded inverter, their MPPT solar controller w appropriate amperage size, the digital color monitor, a BMS that works w the Balqon battery pack, and all necessary p$p.
How can we find the “missing link” BMS? I’ll try calling Balqon next week and see if they know.
JC
I called Victron in Maine today. Very nice people. It’s true, they have come out w/ an upgraded ver of their MultiPlus 3000 inverter/charger and it’s supposedly much more lithium friendly. It will work w/ anyone’s batteries and Batt Mgmt system (probably).
Also true they’re selling their own battery packs and management system. The later will NOT work w/ anyone else’s batteries.
Their lithium’s come pre-packaged in 60, 90, 160, and 200 Ah containers. They want them mounted w/terminals on top, not like AGM’s which can go anyway. All sounds very good EXCEPT their batteries must be the most expensive LiFePO4’s in the U.S. market.
I really don’t want to spend that much for batteries. However, I imagine using their matched set of batteries, inverter, and BCM should produce a finely-tuned system.
With a hoped-for 20% discount from a distributor, the batteries cost 60Ah $1,032; 90Ah $1,383; 130Ah $2,459; & 200Ah $3,074. Weights are 26.5, 35.4, 73, & 93 lbs.
The closest comparison to your 500Ah bank is3-160Ah (480) for $7,378 in a 27″ x 14″ footprint and 219 lbs. One can put 3-200Ah (600) together for $9,221 in a 33″ x 18″ footprint and 279 lbs.
Ouch, for sure. I’d like your comments on just how “too” expensive, if they are, are Victron’s batteries? Is the difference worth it to get their proprietary BCM and panels?
JC
Hi JC —
Great research! I had not seen any published prices on Victron’s lithium batteries yet – they have been “coming soon” for the past two years.
Are they actually available for order / shipping into the the US market now? I know one thing that has held back lithium in the US is the testing and certification requirements necessary to ship a pre-assembled battery. This is where a lot of the additional costs come in versus just buying cells and building your own battery from scratch.
Victron has actually sent us one of the new MultiPlus 3000’s with the improved lithium support to beta test, and I am going to see how well I can integrate it with the Elite EMS we already have. I’ve read the documentation on how to integrate a third-party EMS, and it looks pretty straightforward.
As for Victron’s battery prices…. That is indeed pretty high – but for someone who isn’t comfortable being an experimenter and building up a battery from cells, that is perhaps worth it for a fully supported, warrantied, and pre-integrated system.
Let us know what you decide to do.
Cheers,
– Chris
After the Boeing battery problems I started wondering about fire risk with these batteries. Are the cell temps monitored? If a cell actually did catch fire can it be contained?
-Tom
Hi Tom.. we followed up earlier this year on this topic here: https://www.technomadia.com/2013/02/dreamliner-lithium-worries/
In a nutshell, what we’re using is a different chemistry than Boeing, and not nearly the fire risk. Thanks.
Your observation “…..during my last capacity drain test the Victron battery monitor indicated at one point that -280.6Ah had been consumed, but that a battery percentage remaining was 52%. I’m not sure how they can determine that a battery that has been 58% drained has 52% remaining — I am still hoping to get an answer from Victron support explaining this.”
I can answer this for you. I also use LiFePO4 cells and their a-hr capacity rating is very conservative compared to lead acid. A LA battery earns its a-hr rating based on an easy draw down over 20 hours to full depletion, whereas a LiFePO4 cell gets its a-hr rating in a brutal, 1 C discharge and only to 80% DOD. If a 500 a-hr LA battery was subjected to a 500 amp draw for an hour it wouldn’t make it because due to Puekert Effect would only have about 280 a-hr. The same 500 a-hr LiFePO4 would produce 500 amps for the entire hour and still have 20% remaining. When you draw less than 500 amps, the battery’s capacity is even higher.
In my book, “Lead is Dead”.
I agree completely with your comments on the difference in how lead versus LFP batteries are tested, but that still doesn’t explain the discrepancy in the Victron user interface. It seems like a bug in the software to me.
– Chris
Bob hit the nail on the head when he credited the Peukert Effect. To simply illustrate this with real numbers, a fully charged 225Ah T-105 battery can actually provide one ampere for 400 hours. Thus if only an ampere is drawn for 225 hours, the DoD is only 56%.
Wow. A decade of reading the BNO and other RV forums and seeing the question “can i run my AC with an inverter?”, and the answer from some smart old guys “nope, can’t be done, not practical, to expensive”.
Anyway, have you looked into building your own monitoring and charging system with a Raspberry Pi? Someone above mentioned Arduino, but i think Rpi is more capable. Bedsides all the sensing, switching and managing you would need, it could send you a text to let you know how it’s going.
Thanks for some great info. Now it’s time for the two-year update (grin)
Dave
Hi Dave —
Sean and Louise at OurOdyssey have run their AC off of batteries for years – so there are examples on the bus boards of it being done. But indeed, very few people have gone and proved that it could be done practically.
As for custom monitoring with a Raspberry Pi or Arduino…. I love the idea, but so far haven’t had the time to even begin contemplating a hacking project like that. Maybe someday.
BTW – Victron has a new control panel system coming out this year that allows for remote monitoring and control which should give a lot of cool features in an off-the-shelf package.
And yep, a two year post is slated in the near future once I have some time to do some capacity tests. But the quick summary is that everything has been working great!
Cheers!
– Chris
It occurs to me that a simple change in the pulley diameter on your bus’alternator would solve the problem. If engine rpm is at 1500, changing the alternator’s pulley to place it in an “overdrive” condition will spin it up to sufficiently compensate.
Sometimes when focusing on the electronics it’s easy to forget the mechanics that creates them.
This is a good thought, but our alternator is gear driven directly off of the engine and I don’t think there is any way to adjust the ratios to make it spin faster. Thanks for the idea though!
– Chris
Hey there, I’m a fulltime RV boondocker who also recently took the leap to LiFePO4 with good results.
Last January, I acquired 260Ah (at 13.3V) of some 2 y/o ThunderSky batteries on clearance for about $850 delivered, which is comparable to the cost of some good new AGMs (but weigh 100lb less). The cells have no balancing circuit, yet have remained within 20mV of each other for four months now.
I use a $25 Arduino-like microcontroller to handle charging as well as high/low voltage disconnect on a per-cell basis. My charging scheme is solar only. I count amp-hours removed and the MC puts the same back in, plus a little more to account for coulombic efficiency of around 90%. I try to maintain the bank between 60-80% SoC because my #1 goal is to see if I can 7-10 years out of my LiFePO4s.
What do you think of my chances?
Thanks for stopping in – always a pleasure to encounter others playing around with this stuff. We are too hoping to get a similar life out of our bank. Here’s to the future!
If I am only using alternator and solar power in my RV (no shore power) do I need an inverter charger?
Depends – what voltage does your alternator and solar put out, what are you storing in your battery and what do you need to run you house systems? More than likely your power system is 12v or 24v, and your house system will need 110. For that, you will be highly dependent on an inverter – get the best you can afford. Unless you can run everything off 12v/24v.
Switching the mobile palace completely over to 24v might be more of a project than you want to take on. During a complete tear down and rebuild of the bus it would be much easier. The little things start to be quite the problem: Wiper motors, instrument lamps, relays, pumps (got air bags?)fans and all other manner of annoying little things that you won’t find until they burn out. I’m sure if you took a critical look under the dash, you would shudder. Why not think along the lines of having a separate “house” system and vehicle system. If you are contemplating adding an additional pulley driven alternator, why not designate that for 12v vehicle systems and use the current gear driven alternator modified for 24v service or vice versa? This will save a load of money, time and aggravation in modifying items. You can also remove connections between the engine batteries and the house batteries to avoid discharging the batteries that start the engine.
I always try to anticipate failures and formulate solutions in advance and while a 24v custom starter is not difficult to do, it takes time and getting a replacement when you’re camped out on the playa for The Burning Man, waiting for a custom part is not ideal. Tow service off of the desert is available, but the towing companies that will do it charge for “off road” service at many times the usual rate. For a bus……. ouch. The more of the bus system you can leave stock, the easier it will be to find replacement parts in stock when you need them.
You might even consider going to a 48v battery system. The higher the DC voltage, the better the efficiency of the inverter providing AC power. Smaller wires and connectors are always welcome.
Thank you for all of your information. It’s one thing to talk about theory, but your hands-on experience is indispensable. I have been contemplating selling off my accumulated junk, packing up the cameras and the cat and doing the mobile thing myself. I glad that Karen Willmore sent me a link to your site.
Ken
Hi Ken –
There are a lot of advantages to switching to a 24V house system, but as you pointed out – there are a lot of headaches too.
Certainly the smart way is to go with a hybrid 12V / 24V system to avoid needing to replace any of the old under-dash system, but even then it is still tricky.
I was briefly tempted to go 24V, but the reason we did not was it was just too big of a project to take on retrofitting. Maybe someday if we ever decide we need a bigger inverter, then it would be worth it. Our current inverter is just about as large as you can get on 12V, and having smaller wires and less wire loss would be great.
BTW – getting 24V alternators and starters is not such a big challenge, most buses built more recently than ours (1961) are actually 24V native.
And if we were to ever break down, I can’t imagine a better place to have mechanical issues than at Burning Man. There is more engineering ingenuity out there on that desert for that week than you would find just about anywhere else short of NASA.
Cheers,
– Chris
And not to mention.. many art cars are built out of buses, so thus a lot of bus nuts out there 🙂
Hey Chris,
Sweet article!! I definitely appreciate you sharing your power systems design findings! I’m aspiring to install a system much like yours. Though, my wife has some “reservations” about the idea of letting me design and install it. Totally unfounded concerns of course! 😉 Anyway, you mentioned the folks at elitepowersolutions.com a couple of times.. Would you recommend that I go to them to design a system for my RV? Your other article about power boosting really makes a lot of sense too. A must have for me.. Think they’ll be able to tie all that in as well?
In addition, my wife and I are slowly pulling the trigger on going full-time. The hammer is about to drop! Got an offer on the house yesterday.. Cheers!!!
Hi Sean —
The folks at Elite Power Solutions have been a great resource for battery information and cells and how to protect things with a BMS, but they are not going to be able to do much to help you design your overall RV system – that isn’t their area of focus. They don’t do installation or design work, they are just the US importer of one particular brand of LiFePO4 cells.
But – they are very worth a call / email. Tell them we said hi!
– Chris
Hey Chris,
Oh okay. Thanks again for the info! Can you recommend anyone that would be able to install a similar system?
Sean
If you look back on the post Chris did on the ‘Cost Analysis’ (linked above) – we listed all of the vendors we had checked out. Might be worth checking in with some of the folks doing RV systems to see what they’re up to these days since we first poked them. As we’ve not used any of them, can’t make any specific recommendations.
I was wondering if you have anymore info on charging with solar panels and if there is a recommended charger for lipo4 with solar
Hi Troy – Chris has started some research on approaching our solar install, but we haven’t yet started the project. When we do, you can be sure we’ll blog about it.
Have you considered just setting the Absorb voltage on the
Victron to be equal to the Float voltage and skipping the Absorb step entirely? You would get a complete recharge during the Bulk phase, and then go straight into Float, allowing an automatic sensor output from the Victron to shut off your generator?
You might have also play with the End Amps setting for Absorb if Victron has one. Even if you cannot set a zero Absorb time, setting a very high value for End Amps should still cut off the Absorb part of the cycle. If it does not, that is a failing in the Victron. I am pretty sure you can use that strategy with a Midnight Solar charge controller.
Dave –
To keep the batteries healthy long term, I float them at a lower voltage than is ideal for charging – so I think setting the absorption to be equal to float would result in a slower charge not taking full advantage of our battery capacity.
I’m not sure if any tweaks may be possible with playing around with the “End Amps” setting – I don’t remember seeing anything like this configurable in the Victron control panel, but next time I am playing around I’ll take a closer look.
I’ve heard good things about Midnight Solar charge controllers. Do you hove one? How do you like it?
Cheers,
– Chris
Love the info on the battery system – but one assumption I think is key – number of useful cycles. Having lived with laptops for 10 years – I would say typical lifespan is about 500 discharges, certainly not 1000’s. I’ve never had a lithium battery last (keep more than 50% of original capacity) more than two years with daily use. Thoughts?
Hi Kevin —
The chemistry in laptop batteries is a bit different, and the use case they are optimized for is vastly different than the types of batteries you would use in an RV house system. Laptop batteries are engineered for maximum capacity and for being drained to zero regularly – not for a maximum number of lifetime cycles.
On the other hand, RV house batteries (even lithiums) should never be drained 100% – and this makes a huge difference in enabling many more lifetime cycles.
Also – I’ve noticed that the new Mac laptops that do not have removable batteries have done more work to engineer for more cycles. Apple now rates their batteries at 1,000 full discharge cycles before capacity is diminished to 80%. For most people, that means the battery will outlast the useful life of the laptop.
– Chris
Really helpful post. so much info!
Guys, thanks for the kind words and for spreading the lithium ion information. I can’t believe it’s been a year already since you were here. The software update is here waiting next time you come through Phoenix.
Thankyou for posting your results on your Lithium batteries so far. I would like to get rid of most of the 1000 lbs (1700 amps L16HC) of batteries we have to carry around but it doesn’t look like it will happen anytime soon. I too am a Technomad so I need electricity. We have 1580 watts on the roof. It does spoil the looks of the bus a bit but thats life. With that much shade we have never had the need for AC. We will be leaving Oregon in a couple of weeks to head south for our annual trip to Mexico. I can’t wait to get on the road again.
Jerry
Great post, thanx for the effort and sharing.
I am in the middle of designing a upgraded RV for our family. All dry camping in very remote areas with terrible roads. Weight is a major issue and I have been considering Lithium given that the electric car industry is starting to make it affordable.
As a ground up design it looks like a cost break even to go with 24V using a second 24V alternator and solar. I have found better performance 24V air conditioners, many Sharp LCD’s use 24V, 24V LED lighting, water pumps, macerators, refrigerators, fans, etc. are available.
In your situation (lots of legacy 12V) you may consider (for items that can be isolated from ground) simply running 2 units in series to make a conversion to 24V most cost effective. It does seem that I may be able to use a 24V air conditioner (check out http://rencoolusa.com/dc-products/split-unit-air-conditioner/) using solar and battery alone. Prudence does include the use of a honda eu1000 (900W AC at 26lbs) as a backup for bad solar luck. There are several other options driven by new rules that you can not idle your truck at rest stops. Most trucks use 24V.
Good luck
Ron
Indeed there are more options for DC cooling once you go up to 24V from 12V.
But no matter what, it will take a LOT of solar and a big battery bank to be able to get much air conditioner run time. How big of a solar install are you planning?
The little Honda generator will probably not be able to keep up with even a small air conditioner either.
I’m eager to hear more about your project, and thanks for the great lead on another DC AC option.
– Chris
OK
Now you’ve made me write some things down.
A little background. We are a family of four that enjoy kayaking, mountain biking, hiking and motorcycles. We have been getting out every other week end for over 20 years. Currently using a long wheelbase extended chevy van with 2 T105 batteries (alternator charged), 3cu ft 12V fridge, Fantstic fan, water tank, sink microwave, sleeps 4, kayaks on top, one motorcycle in front, another in the back with the mountain bikes. Can’t recall ever staying in a location with power.
Stepping up (while the kids step out) to a long wheelbase, extending body high roof sprinter van and adding air conditioning, solar panels, shower and toilet to the above list while removing a 2 person sleeping area. Vehicle purchase is planned for the summer of 2013.
I agree with everything you wrote but we may be in very different situations. Check out this site http://www.moorepage.net/heatloss.html . The very simple (and only good enough for an estimate) spreadsheet helps you understand the problem. For us:
Heat gain calculator Gain, in BTU/hr = (surface area / R) * temp diff
BTU / hour â—Š Infiltration = cu. Ft. * R * air changes/hr * temp. diff
Inside temp = 72 Outside T 105
Element ft^2 R °F diff BTU Gain
” Lighting Watts 100 341
” People 2 682
Total insides 1,023
Floor 132 7 33 622
Ceiling 132 9 53 777
N wall 132 7 33 622
S wall 132 7 33 622
W wall 36 7 33 170
E wall 36 7 33 170
Windows 5 1 33 165
â—Š Infiltration, area 792 0.018 33 141
0.30
Total, outsides 3,290
Total, ins + outs 4,313 BTU
So this large van (with 2″ of foam wall insulation, shielded windows, canopy shade on sun side, minimal internal heating) should only take about 4300 BTU to cool. Other estimates are roughly the same.
Check out http://feddersusa.com/AZ7R05F2A.html#tab2 where 485W provides 5200 BTU. Verified here http://www.wind-sun.com/ForumVB/showthread.php?16201-Fedders-5000-BTU-A-C-test .
I add two large Sunpower high efficiency panels at 320W each, small 900W gen to fill in holes, run the van for 10 minutes in the evening to pre-cool, use 120 AHr 24V lithium to control weight.
So I built a little spreadsheet to see if this could work. The AC always runs from battery, the generator, or alternator, or solar simply charge or share the load.
12 to 4 4 to 8 8 to 12 12 to 4 4 to 8 8 to 12
Activity net watts sleep sleep wake out out dinner
Fridge 53 0.4 0.4 0.4 1 1 0.5
AC 500 0.4 0.4 0.4 0 0.25 0.5
Laptop 30 0 0 0.25 0 0 0.25
Lights 12 0 0 0 0 0 0.5
Microwave 1000 0 0 0 0 0 0.05
TV 40 0 0 0 0 0 0.5
Satelite 28 0 0 0 0 0 0.5
Fan 23 0 0 0 0.5 1 0
Fridge 21 21 21 53 53 27
AC 200 200 200 0 125 250
Laptop 0 0 8 0 0 8
Lights 0 0 0 0 0 6
Microwave 0 0 0 0 0 50
TV 0 0 0 0 0 20
Satelite 0 0 0 0 0 14
Fan 0 0 0 12 23 0
net load w/hr 221 221 229 65 201
in 4 hrs 885 885 915 258 804 1496
Air temp 85 85 90 100 100 90
Sun angle to panel, ave 0 6 38 77 38 6
Panel x 2 320 0 66 384 597 377 65
Gen, minute 120 0 0 0 0 0 100
Alt, minute 2000 0 0 0 0 0 15
Generator, W 0 0 0 0 0 200
Alternator, W 0 0 0 0 0 500
Battery, 24 2880 1460 839 1462 3590 3584 2345
120 max % depletion 0.70
A hr
The day is broken in to 6 4 hour blocks. In the first group the % on time for each load is shown. The next group is the associated load in W-Hrs. I assume 14 hrs of sun with output reduced at low sun angle. The bold line (Battery) shows the remaining charge at the end of each 4 hour period with the loads and sources as shown. Anything over 2880 is not used but shown to indicate available power (may be good to simply run the AC for a while as apposed to the fan that is just intended to get the internal temperature the same as the outside temperature while we are ”out”.
Still need to run the van for 15 minutes to pre-cool the cabin and run the generator for about 100 minutes during high load at dinner (cooling, TV, laptops, Sat.). I would let the internal temp rise until the AC duty cycle is 40% while sleeping.
So this is the concept. The AC is 115V so I added 10% loss for the inverter. With no idle truck rules, some new DC compressor products and continued growth in off grid solar I would expect a DC unit that would match the Fedder performance shortly.
For our little van, I think it is just do-able. A whole bus may be a different story but with insulation, window removal and lots of panels on the roof …….. maybe.
Currently all just paper and hot air but seems there may be a successful path.
Ron
Sorry about the table formatting. Let me know if you would like me to try the tables in a different format.
Hi Chris,
My goofy dogs had to go outside so I checked email (3am) and saw your message.
The starter is the easy part. A 24v one from a gm 4905 will drop in. Its fed by a relay so its contact supply could be changed to 24v.
Ditto for the alternator/regulator mechanically.
The big 12v bus loads I can think of are:
1) The heat/cool system
2) two big 12v contactors for general/reading light loads
3) original bus bathroom blower/pump
4) the defroster blowers.
The defroster can be changed to 24v (relay driven too).
If your conversion dispensed with 1,2 and 3 then bus wise I think its practical since remaining loads are lights, instruments and a few engine control air solenoids.
There are a few other details like the bus alternator power with has it own contact in the master switch(good) and there is a special alternator relay that indicates alternator is running that may have to be swapped.
The maintenance manual has great electrical diagrams. I may have the alternator diagram for a 4905 somewhere for reference.
Hi Guys, Thanks so much for detailing your progress. Neat to see convergence between RV systems and off grid solar/wind technology where generators are used more and more as backup power. This is definitely the future. Have you considered switching to the 24volt version of the bus alternator? Its rated at 225amps which is about 3kw, enough to comfortably support one of the modern minisplit units. Figuring out how to merge the 12volt bus electrics would be a challenge (ie, fun) of course.
-Tom
Hi Tom –
I’ve often daydreamed about what it would take to go to a 24V system. We could get a more powerful alternator, wouldn’t need such hefty battery cables, and the 24V version of our Victron inverter actually would be able to charge the batteries faster too.
I haven’t heard of anyone converting a 4106 to use 24V, but I imagine it can be done. But I’m not sure if it can be done in a cost-effective way to make the project worthwhile.
I wonder what it would take to change to a 24V starter motor?
The rest of the 12V loads could be driven via a DC-to-DC converter I think.
Anyway – if you have any advice or leads on how to make this possible, I’m sure some others reading this would love to know more! As you said, this stuff is fun… 🙂
– Chris
Thanks for the write up, guys. Greatly appreciated. I’ve factored in LiFePO4 as a possible battery solution in my rig.
Questions:
– What are the dimensions (length, width, height) of your battery pack?
– If you don’t live full time year round (for example, 6 months on and 6 months off), would you still have invested in LiFePO4?
Thanks a lot
Hi Malcolm –
The dimensions are 21″³ x 14″³ x 11″³ and weighs just 140 lbs (here’s a link to the post where we talked about that: https://www.technomadia.com/2011/08/we-built-a-lithium-ion-battery-bank/)
And for the second question, that’s far too hypothetical of a scenario for us to answer. But considering one of our primary goals has been to play with cutting edge stuff – probably. But us not living full time on the road is something that’s not even a consideration for us.
Hello Chris I’m sending this comment from Northerner Mexico in Chihuahua. Me and my uncle run a large Pecan Nut farm and move back and forth to take care of it. We are vary interested in putting a large Lithium battery bank in are RV and we already run are home on Solar Power so we want to run are RV on solar too! Do you have e-mail that we could contact you on for more ideas.
Hi Jessie – you can reach us at us@technomadia.com (as plastered on every page of our website :)).
Great article! If you are looking for a higher output from your engine alternator, Put a smaller diameter pulley in place of the one on the alternator now. They are quite inexpensive and can be found at auto parts and truck parts suppliers. Do keep the alternator’s speed within the manufacturer’s spec’s. Most alternator manufacturers have on-line information and formulas for calculationg your required amps output at whatever engine rpm you want to run at.
Al
That is a great tip, Al.
In our case though, our alternator is gear driven directly off the engine, and is not powered via a pulley.
We might someday mount a second auxiliary pully-driven alternator. And if we do, playing with diameters might be a great way to optimize power output.
The only problem I would see for using a single cell ballancer for multiple cells in parrallel is having it draw enough current to ballance when charging.
One question I have is how the wires are connected to the battery. With four screws rather than a large bolt, standard crimp connectors won’t work.
Hi Blars —
Indeed, ideally the balancers would be able to put a larger balancing load, and we could actually add multiple passive balancers to each of the cells in parallel to accomplish this.
Elite sells these passive balancers for just $9.
Our normal charge voltage doesn’t push the cells to the balancing point, so it isn’t an issue. When I want to balance – I set the Victron to a very very low charge current so that I don’t overwhelm the single balancing shunt.
As for connecting the battery cables – Elite provided screw on ends that we crimped to the cables. I used two positive and two negative wires in parallel to handle the load since #0000 wire wasn’t available, nor could I figure a way to attach a #0000 wire to the battery with these connectors even if I had found some when I needed it.
Thanks for the great questions!
– Chris
Hi Chris,
thanks for this awesome report. I looked forward to this for quite some time, since I followed all your last posts on this technology.
I am in the planning phase for such a system myself (also with Victron), but with Winston batteries in my case. Two things intrigue me the most:
1.) How do you prevent over-charging from the Victron or the engine alternator? The Victron shuts itself off at 14.2V, as you say – but what happens in non-perfectly balanced state, when one cell is above 3.8V and a power cut-off is initiated? Or when the alternator continuously charges, and the EMS shuts off? In this case you cut off the connection to the Victron (because battery is disconnected), but you lose AC and Inverter functionality as well?
2.) I just realized with this post, that you only have four balancer and sensor boards. This means, that the packs of five cells (each forming 500AH 3.2V) are not balanced inside? As far as my tests go, this is OK with starter applications (short, hard drawal of power, but directly afterwards charging the pack), but not with deep-cycle applications? In deep cycle, the individual cells tend to drift away from each other, resulting in a potential damage because of under/over voltage. I am just interested whether you measured individual cells as well… I would bet after one year, that the individual cells inside a 5pack are already not balanced anymore. (This was the case in my testing, at least…)
That´s why I tested with up to 16 individual balancer boards (4x(4x100AH)), each with separate cutoff for high voltage protection and low voltage protection. The only problem I have is the fabulous Victron – when I cut connection because of over voltage protection during charging, the inverter stops working. Currently we investigate in switching off the internal charger with VE.Configure, so that the inverter/power assist/power shave still works.
I enjoy reading your posts! Keep up the good work…
Hope to hearing from you.
With my best regards, Martin.
Hi Martin –
It looks like you have done some awesome research of your own – I’d love to compare notes. Have you blogged about your project anywhere?
In answer to your questions:
1) I’ve played around with different configurations of the contactors. At first we were intending to use a battery isolator (diode style) wired up with the contactors so that the battery could still be charged when the LV alarm is triggered, and discharged when the OV alarm is triggered. This would have been pretty foolproof, but would have required a huge and expensive battery isolator to handle the current demands, and in the end I’ve found that this was needlessly complex. In theory – the alarms being triggered should be a rare occurrence, and that has proven so far to be the case.
Especially since the cells seem to have no problem staying balanced over time.
The one place the OV alarm risks getting easily triggered now is when charging off the alternator (though I think I might be able to regulate the alternator peak charge voltage down) – but when that trigger happens in my tests the inverter is still able to be powered by the bus alternator and starting battery which are still in the circuit and in my testing it has worked well. But I try to avoid this situation by turning off the bridge when the battery is near 100% unless we are running the roof AC all out. I’d rather reach a destination with the battery at 80% than keep the batteries constantly bouncing into the OV alarms while charging at 100%.
2) The 5x100Ah 3.2V combined cells are wired in parallel (with 100A fuses as bridges in case a cell shorts so it can’t harm its neighbors) so that they are always balanced with each other and thus need only one sense board for the bunch. This was how Elite Power Solutions instructed us to wire the battery, and in this configuration they told us that other balancing/sense boards would be redundant.
To test the individual sub-cells to confirm balance, I suppose I would have to dismantle all the cross-connects on the battery bank. Do you really think that is a concern? Elite was convinced it would not be, and with cells wired in parallel I can’t understand how a cell could ever get out of balance.
What sort of results have you seen?
As for hacking the Victron – let me know if you figure out a way to control the charger in response to a trigger. I know the newest models from Victron have a new control port designed to interface with their own lithium batteries – have you looked into this yet?
One other question for you – why Winston batteries? Can you share some more about your own research into picking a cell provider?
Cheers,
– Chris
Hi Chris,
interesting how try and error on different continents goes the same way. So far, I did not put my findings on the web – I wanted to test this out for myself at first, afterwards going public with it. Furthermore, if you are experimenting with this technology, there is virtually no one you can talk to about it, few even know there is this technology. This is strange, when you take into account that in Europe you have a severe weight problem – trailers are only allowed up to 3.5tons, and the average RV stays below 5tons. Lithium is a perfect choice for these vehicles – not talking about all the other advantages these batteries have. The main thing over here is getting the charging/discharging foolproof – this is not ready for the market yet (if you exclude the USD6000 Victron/Mastervolt products).
I experimented with diodes as well, but put then aside because of cost and voltage drop issues. I am now using MOSFET switches instead – minimum voltage drop, minimum power usage, switching capacity (right now) up to 260A / 12V. With these, I can switch off DC-DC Charger, Solar and AC-DC chargers in case of over voltage, as well as switch off all 12V devices (Inverter) in case of under voltage.
Interesting is the cell balance issue. I am happy to hear that you have no problem with this so far – what intrigues me is if this would be the case if you would have deep cycled your pack more. How many cycles does the Blue Power Panel read out? I read in a few posts of you that you were not boondocking that much… Perhaps this is why.
The advice from your reseller is a little bit odd, to say the least. Every battery suffers from cell variances. Every lithium as well as every lead-acid. And if you hear around your fellow bus addicts, if they change their battery pack it´s because of one battery out of the pack gone bad, while others are not new, but still usable. And even this defect battery is perhaps usable in theory, but one of the six cells inside has gone bad, making the whole battery (and in consequence the whole pack) unusable.
While these variances are absolutely tolerable for quite a long time in lead-acid batteries, you get lots of problems with this in lithium configurations, because lithium goes bad from ONE over/undercharge, while lead-acid is quite tolerant against this mishandling. This is why you don´t balance lead-acid batteries – because they can cope with it for quite a long time. Lithium can´t. Since every cell is a little bit different, it behaves a little differently during charge and discharge.
Theoretically, every cell in a row SHOULD balance itself with and against its neighbors by varying its internal resistance depending on state of health and therefore absorbing/giving more or less power during charge than it´s neighbors, balancing themselves over the rail they are connected with. But bevause of slight variances and drifts, eventually (especially in high load situations) these cells are in a situation where one single cell in the rail is running into over/under voltage and dies.
That´s why usually every cell is being balanced – at least in the configurations I know of. {Perhaps this is typical german over-engineering – if so, please let me know ;)}
All of this only applies to deep cycle situations – if you don´t deep cycle, you can get away without balancing. A european university made a test with a winston battery cycling 10% of the capacity with 1C. After 13.000 (!) cycles they stopped the test, because there was virtually no wear down in the cell detectable.
This (sort of) answers your question why I use winston batteries – they are available, you get single cells of significant capacity if you like, and the above test of the university is very impressive. Furthermore, you can charge them without a heater at down to -40 degrees C. No thermal runaway, no risk of fire or explosion – they were just a sensible choice to make. So far, I have no bad things to say about them.
The charger part of the multiplus cannot be switched by a trigger, as victron told me.
The lithium system from Victron is connected to the Lynx System with four modules, which interfaces to the bus system of the multiplus. There is a separate interface doing all the necessary calculations and switching batteries and multiplus on and off.
Best regards,
Martin.
What a great report Chris….exhaustive, and complete. You are on the cutting edge of the Lithium Ion battery frontier, and we appreciate the work, research, and long term experience you are going through that will benefit all of us who are looking to this battery technology to make our Technomad travels more flexible and fulfilling!
I’ve been waiting for this report. Thank you , thank you for testing it, figuring it out and telling us how it does in the real world. Terrific write up. I really hope the industry starts tailoring these for the RV world.
I think one of the biggest advantages of your system is that you can use 80% of the battery capacity. It’s like adding a whole additional lead-acid battery but in a smaller foot print and much less weight. In an RV, that is huge! Well, even better because you don’t lose power as the battery depletes like in a lead-acid.
One other thing, I am interested in is how to handle cold weather charging, tho I suppose you just avoid it altogether.
We’ve heard of folks who keep an electric blanket or space heater in their battery bay to warm their LFP up before charging. Which if we found ourselves needing to charge in very cold weather is what we’d try. But considering we have no heating system for the bus, that’s an unlikely scenario for now 🙂
According to Elite Power Solutions, the official temperature rating for our cells is -20 to 65 C or -4 to 149 F.
That is a pretty wide range that should cover most every situation we encounter.
They did recommend not charging the batteries quickly though until they have warmed up above freezing, and this is where I’ve heard of battery heating blankets sometimes used.
Hey Chris,
Great post, we really enjoy watching your adventure into lithium. When it is all sorted out I’m sure us late adopters will dive in. Would you be willing to share how you bridged your coach alternator to your house bank? We have the same coach side set up, our battery bank consists of 6 4D AGMs with a Magnum Inverter. Running the AC off the engine alternator would be a really great upgrade.
Cheers,
Steve
Our LFP batteries are in the bay that the bus used to use for the AC blower chamber when it was a seated passenger coach. There was an already existing heavy gauge DC power cable that runs from this chamber essentially straight back to the alternator.
I used the high current Tyco contactor, wired up to a switch to let me control whether or not the bus house system is bridged to this cable and tied into the bus alternator and starter battery.
It is pretty simple, actually.
Eventually I want to put a smart switch in that automatically disconnects when the bus engine stops so that I never accidentally drain the bus starting batteries while camped.
Loved the tech post, very well laid out and understandable. One more reason I enjoy your blog, it feeds my techie side on the newest ideas for RV life. :c)
Great write up Chris. Could you list a “What’s in the Bag” for us, like listing all the components and their initial costs, so we get an idea of just how much we’d be looking at cost wise to do what you’ve done?
Thanks, Russell
Russel – check out the Cost Analysis post linked above. We already posted that last year 🙂
Thanks Cherie,
I must have overlooked that post.