Building 100 AH LiFePo4 Battery Box

I truly grok the "heat and bug" seasonal limitations... (Sorry to the non-Heinlien fans for the reference).

My friend got out of the hospital a week ago and was back in by Sunday night, so things have been touch & go, but right now, it's looking like they may have sorted him out, and he might be released again next week, depending on the results of the next round of tests.

In the meantime, I've been trying to find out as much info on the communication protocols of the BougeRV 60-amp controllers, and as far as I can tell, there's no provision for them to work together with others, even if they are the same brand & model. That doesn't mean one can't use them in parallel, but one is likely to need to log into each separately to manage them.  It's looking more & more like the BougeRV controller is really intended for systems where it's the only controller in the system, so if one is OK with the limitations of an 800 watt charger (12 Vdc) or a 1600 watt charger (24 Vdc), this is the one to get, but if one has much greater needs, it might be better in the long run to go with the Victron system. I can possibly try to use both of the BougeRV controllers at the same time, but I don't have enough of the same type of solar panels to max out both controllers - I can run 1 with 800 watts of panels and only 400 watts for the other one until/unless I buy another pair of 200 watt panels.

I do have a pair of 36 Vdc rigid panels that are a pretty good match for the Victron 30-amp controller buried in the box, so I can drag those out into the yard and add them to the mix, but I don't think it's a good idea to mix those panels with the 24 Vdc Harbor Freight panels.

Clearly a win for the Victron system, as they can be linked via Bluetooth and you end up with one as the master controller and the others as slaves, so you change settings on one and the changes are propagated automatically to the rest of the network. Their network can also include other devices, like their Smart Shunt (which I have, but was saving for the 24 Vdc battery build).

Should be sunny all weekend, so hopefully I can get some charging data from one of the BougeRV controllers and the group of Victron controllers too, but I'm also trying to cobble together a minimal laptop to load Linux onto, and copy some videos to, so I can deliver it to the hospital and help keep my friend from going stir crazy and being a pain to the staff... It just needs to be able to run Linux Mint, and VLC for this to work.

Finally getting back to this thread now that some of deep summer chores on on the wane...

The 12V build that I described above was tested today in some water pumping and had a somewhat surprise result.  For details on the pumping set-up see my entries here -- https://permies.com/t/179996/Sprinkler-pumps-shallow-pumps-irrigation

So even though I'm mixing brands, I decided to try linking (in parallel) my 100Ah battery build with a recently-purchased 100Ah Ecoworthy 12V LiFePO4 battery.  Bluetooth allows me to connect to each separately for monitoring parameters during operation.  The two batteries are supporting a 0.75 hp 120V electric water pump pulling water for our garden.  The set-up with the 3000W pure sine wave inverter is shown below....tonight's test had the system running for about 30 min.

While all worked well, I was curious about the imbalance between the two batteries in terms of amp draw. Thus, when using two Ecoworthy batteries purchaed all at the same time and starting at the same state of charge, they both equally split the 60A load into 30A to each battery.  In the configuraton shown below, the Ecoworthy was drawing 40+ amps and the home-build around 20A or a bit less.  The BMS in the home-build is set to deliver 100A from the battery if need be, so it doesn't appear to be limiting the amperage output this way.  When I used the battery alone to run a vacuum cleaner some weeks back it delivered 40A no problem, so this "seems" to rule out a connection/wire bottleneck, yes?  Any ideas here regarding the imbalance?  As an aside, the BMS in the home-build was keeping the cells themselves balnced just fine.  Thanks for any suggestions or questions....

I can only guess that the 2 different batteries, even though they have the same voltages, have different resistances, so there's a current imbalance.

While I don't have the equipment to measure battery cell internal resistance, all batteries (& cells) have an internal resistance, and one of the biggest benefits of buying cells from a reputable vendor, is the matching process, so that there's documentation of the specs, & all the cells at least start out contributing nearly equally to the loads, and charging nearly equally from the charging. It's unlikely to be perfect, but balancing takes care of the rest.

If you know what the internal resistance is of the set when you start, you can generally use that number later, to shop for additional cells/batteries to add to the system however, as technology marches on, the trend is toward lower internal resistance, for higher efficiency cells, so at some point, you might be better off just accepting the newer/higher efficiency that also usually comes with a lower price tag too.  It's not the end of the world, but in your example, the more efficient battery will deplete faster, so if you're needing the full name plate capacity of the combined system (200 amps), you'll only have a chance for that while both batteries are contributing (& I wouldn't advise pushing it past the weakest link).

For lighter use, you're fine as long as each bank has its own BMS and is staying balanced.

I have seen Andy on the Off-Grid Garage YouTube channel use such a meter, but I haven't yet felt moved to buy one. I don't *think* they're too expensive, I just haven't gotten around to it.

Well, it wasn't what I would call done yet, but it was pressed into service, and I have learned from the experience, how I wish to alter it going forward.

We have gone to visit Wheaton Labs for a week (as SEPPers), and rented the Allerton Abbey cabin. It has a rudimentary solar system, which was (I'm lead to believe) cobbled together with old parts laying around, etc. It only provides some basic inside lighting for a few hours, but the batteries are old lead acid batteries, that are long past their prime, so even if we shut off those lights before they quit, they are still completely dead by morning.

Stepping back to the beginning of this trip, we elected not to bring the much larger capacity 24 Vdc system, because we were running short of cargo space, and really didn't HAVE TO have 120 VAC, so the smaller DC only box seemed plenty. Turned out, I'd mis-calculated the load of running both the DC refrigerator and the DC freezer, plus the drive ended up being over 2 days, and by the time we arrived, the 4 KWh battery was depleted, and it was dark, so no solar was available to recharge it until morning.

I also discovered in the morning, that I'd forgotten to pack all the PV cables, so I could only connect 400 watts of panels, and it was somewhat cloudy on Monday too, so not much solar harvested. On Tuesday, we went into town, and I found a solar dealer who was willing to sell me some 10 gauge PV wire and an MC4 connector pair, so I could connect the other 400 watts of panels (I only brought 800 watts this trip because our usage wasn't expected to be that much without AC appliances). It turned out that I was also missing some ring terminal connectors too, but those are easy to find everywhere.

I didn't have the Allen wrench to tighten the connector on the circuit breaker terminals, so I bypassed them. It won't pass a code inspection, but it does work to charge the battery. In our best sun this afternoon, we were charging at over 600 watts, and overall we got the batteries charged up to 25% capacity, while still running the DC loads and that should be plenty to make it through the night until we get more solar power.

As far as the learning part of this, I've learned that I really should make sure I have a way to charge the 12 Vdc system with the vehicle, while going down the road, even if it is only a small charge, like 8 amps or less, and I should always bring tools!

They sell these chargers that go from your vehicle battery through the firewall (or underneath if you have a truck and are going to the bed). Mine charges up to 500W but that's also limited by the controller in my power station. It's pretty sweet because 2h of driving will charge 1kWh. They now sell ones with higher capacity too, I'm not sure what the maximum draw on a car battery would be.

If you take this thing on road trips a lot, I'd recommend it. $200 on Amazon or so I think.

Do you have a thread or video on how you built the battery box? That sounds interesting.

M Pearson wrote:They sell these chargers that go from your vehicle battery through the firewall (or underneath if you have a truck and are going to the bed). Mine charges up to 500W but that's also limited by the controller in my power station. It's pretty sweet because 2h of driving will charge 1kWh. They now sell ones with higher capacity too, I'm not sure what the maximum draw on a car battery would be.

If you take this thing on road trips a lot, I'd recommend it. $200 on Amazon or so I think.

Do you have a thread or video on how you built the battery box? That sounds interesting.

Most of the build for this box is in this thread, even though mine is most certainly NOT a 100 Ah battery (314 Ah), because I hadn't finished it enough to be comfortable submitting it as a small DC solar system badge bit yet. It's close, but really the hold up is sorting out where the best places are, to mount the exterior sockets and connections. I even brought my drill with me, to maybe work parts of that out.

As far as taking frequent road trips, this is kind of the maiden voyage of this 2017 Dodge Grand Caravan GT. We bought it a few weeks ago as a cash private sale, got plates and tags, and hit the road. Still learning about the various issues and hopefully minor repairs it needs, but I don't frequently get enough time off to go on many road trips, plus, this van gets pretty poor fuel economy compared to our last one (a 2013 Dodge Grand Caravan that we bought new from a dealer). I've no problem with modding the vehicle, but a trailer hitch is probably the next step, since this trip has proven that it's a challenge with 2 Great Danes, wife, luggage, and food for all (we feed raw, so the 80 qt freezer was mandatory, and 55 qt refrigerator was mostly for human food).

There are other badge bits for expanding capacity and/or adding permanent 12 Vdc electrical upgrades, and I will probably do at least a dedicated permanent DC socket rated for 20-30 amps. The van already has a small capacity inverter for 115 Vac power, but I don't think it's large enough to be terribly useful. I might upgrade that after a trailer hitch? Gotta get some more interior space and luggage capacity first.

Just to make it back home, I'll limit the BMS to a 7-amp charge, & temporarily wire it to one of the 12 volt outlets in the van.

As an aside, Allerton Abbey is a comfortable cozy place to stay, as far as cabin rentals go 🙂 - I highly recommend it if you want to make a pilgrimage to Wheaton Labs!

That sounds like a fun and educational trip, Allen....thanks for posting this.

I think one example of the charger that M. Pearson was referring to is demonstrated here, although it comes as part of an add-on to a portable power unit:   https://www.youtube.com/watch?v=r29jk4OyOJs    

Victron's version is shown here....and I'm immediately intrigued!  
https://www.amazon.com/Victron-Energy-24-Volt-Battery-Charger/dp/B0F43Z9R53/ref=sr_1_1?crid=11SA759Q2P2XE&dib=eyJ2IjoiMSJ9.wQqVjiogszb9YmxEDHxJJwNXheb2W-VzltHjPLEfihAKoiCWMBX_uaHc41TB59AqGrAGhQDWFVvLJZNT3wDa3MnfCIsKDtgycSW5tZDG3Y21bE_kwl00Gs03KbbalLlIA8ZnTPmLRv8QHgjVTfrjQpJaFdaMG_KF1RXGHp4P-HSfDqyq_BpSAdB-aO5lnDQFgczMpo_TLrs1aGn8TBu4RdKQB8Kd6fPSkGPOr2d0u4yhrGBDPkatCJEA5_96gJoNT3q0z5AmSCMgUWIBsWRYhRJ2hnCjkJcnm5cYhGzVLAY.XQScvxBCHoLmgauk0P9b5OBMI5Ds775aYcXGT9a6qj8&dib_tag=se&keywords=alternator+charger+dc+to+dc+bluetooth&qid=1792060582&sprefix=Alternator+charger%2Caps%2C215&sr=8-1

I had not heard of these until now and they look like a more simple, albeit lower power alternative to adding a generator to your engine serpentine belt that I'd also seen advertised.   The alternator charges would make sense for most individuals it seems.

That wasn't really what I had in mind, but thanks for the suggestions.

At least for a 12 Vdc LiFePO4 system, the stock alternator output voltage is high enough to charge the batteries, so as long as the BMS is configured for such, it will charge without blowing a fuse or tripping a breaker.

It is a 1600+ mile trip for us one-way, and a trickle charge for the entire trip will surely be enough to top off the batteries as needed, plus, now our solar is running well enough that it may not be needed at all.

In any case, I'll have some more data on how well it worked by the end of the trip, so we can all learn from the experiment.

Allen Jackson wrote:....

At least for a 12 Vdc LiFePO4 system, the stock alternator output voltage is high enough to charge the batteries, so as long as the BMS is configured for such, it will charge without blowing a fuse or tripping a breaker.

Out of curiosity, how does that work with respect to surges in either amps or voltage with variable engine speed.  I realize that there are voltage regulators in car electronics, but if, say, the amperage is beyond what the BMS 'recommends' for the cells being managed, does it simply shut off the ability for the battery to accept charge and then recover once the amps are back in range?  If so, I could see where a separate charger is less of a concern....the BMS essentially serving the same function.  Or?.....

Thanks!

Since current draw demand is always determined by the load, telling the BMS to limit charging to 8 amps would do just that - until changed, that charging circuit won't draw more than 8 amps. The voltage may surge or ebb, and the current can drop lower than the 8 amps if the supply can't provide 8 amps, but excess current is what would blow a fuse, so the BMS serves that protective role.

The BMS is also the protection from over-voltage, so if the supply voltage exceeds the threshold, the BMS will shut off the charging port.

A solar charge controller is kind of like the voltage regulator for the solar panels, because that voltage can swing widely & wildly multiple times a minute through a much larger range, vs. a car alternator & voltage regulator, that will keep the system voltage within a much narrower range that just happens to be in the acceptable range to charge a 12 Vdc LiFePO4 battery 😊

The only danger is from the BMS deciding that the food source is so yummy that it gets too greedy, too fast, and starts blowing fuses/breakers.

Here's a good example of the Victron networking - I have 2 different size controllers running in this network, but no matter which one I log into, I can view the individual performance of that one AND the total performance of the network overall 🙂

SUPER convenient!

Also, in one day's worth of solar with this setup, my battery charge level went from 5% at the beginning of the day, to 93% by the time the solar power was waning. All the while running both the refrigerator and the freezer, and recharging numerous other devices that used USB charging. I fully expect to be fully charged by mid-morning tomorrow, and pack up the solar panels in the afternoon, to leave the cabin Saturday morning, and being able to trickle charge along the way should keep the system nearly full by the time we get back home, even though there's likely to be an overnight stay in a motel, with the appliances still running at night on battery power - with the vehicle power shut off.

Although it's rather the wrong time of year for the following suggestion, are you using the roof rack of your minivan while traveling?  In a pinch, would strapping down two of your solar panels on that roof supplement in any significant way the trickle charging from your vehicle alternator....during mid-summer of course with the longer days?  I realize this could cause too much drag on the car, but perhaps with some sort of roof spoiler to reduce friction? So nice to see the utility of even these small battery set-ups, the recharging diversity that one can implement, and the utility of the bluetooth monitoring of it all.

Edit for additional tangential question:  Will sodium ion battery cells require a BMS purchase specific for that chemistry or will the same BMS's sold for LiFePO4 be usable for sodium ion?  I could see where it might just be a matter of tweaking the parameters controlled by the BMS to allow its use with that chemistry, due to the different discharge curve and perhaps other idiosyncracies of those cells but don't know for sure.  Just looking ahead to potential future builds.....  Thanks!

M Pearson wrote:Do you have a thread or video on how you built the battery box? That sounds interesting.

I have gone ahead and submitted it for the small DC solar badge bit, so all of the details are in one place.

I think it's ugly as sin, but I can't argue with its proven functionality, as we've been living off it for the past week? The food in the freezer is still frozen hard, and the food in the refrigerator is still cold... Our phones & tablets are charged up, and our rechargeable lights are too. Can't beat that - the wife is content with the camping trip, I'm not in the dog house for dragging them all the way out here, so all around, it's a win😊.

https://permies.com/wiki/14/112937/pep-electricity/Small-DC-solar-system-PEP#3995265

John Weiland wrote:Although it's rather the wrong time of year for the following suggestion, are you using the roof rack of your minivan while traveling?  In a pinch, would strapping down two of your solar panels on that roof supplement in any significant way the trickle charging from your vehicle alternator....during mid-summer of course with the longer days?  I realize this could cause too much drag on the car, but perhaps with some sort of roof spoiler to reduce friction? So nice to see the utility of even these small battery set-ups, the recharging diversity that one can implement, and the utility of the bluetooth monitoring of it all.

Edit for additional tangential question:  Will sodium ion battery cells require a BMS purchase specific for that chemistry or will the same BMS's sold for LiFePO4 be usable for sodium ion?  I could see where it might just be a matter of tweaking the parameters controlled by the BMS to allow its use with that chemistry, due to the different discharge curve and perhaps other idiosyncracies of those cells but don't know for sure.  Just looking ahead to potential future builds.....  Thanks!

Ironically, on our return trip, we will be carrying the solar panels on the roof rack, but they will be folded up, not deployed. It's not worth the bother at this point to try to rig up something to be able to use them going down the road, when they won't need more than the trickle charging I can get from plugging into the 12 Vdc outlet inside. Putting the panels on the roof will free up a bit of interior space to ease the trip home.

As far as sodium batteries, it's my understanding that they have such a different charge/discharge curve, that one would need completely different gear to manage them.

As a follow-up, the vehicle charging cable seems to help a little, but it's not keeping up with the load on the battery. This merely tells me that I probably have to run a dedicated 10-gauge pair with a separate breaker to an XT-60 outlet for this use.

This is not an issue for the remainder of this trip, because there's plenty of juice left to make it home today, and our forecast is for great solar for the rest of the week, so I can place the panels in the back yard, & let them do their thing.

We made it home safely and there's 55% capacity left in the battery. We won't even unload the van tonight, and just let it run until morning

Allen Jackson wrote:We made it home safely and there's 55% capacity left in the battery. We won't even unload the van tonight, and just let it run until morning

Just such an odd coincidence.  I travelled a bit this weekend to visit family.  My brother and his wife pulled up in a "new" (used...1998) conversion van with much of the same intent as yours. They had a Jackery power station, a 12V fridge/freezer combination, stowed solar panels for recharging, a trickle charger from the 12V port inthe van for the Jackery, and a sleeping bunk built in.  As his lifestyle has been pretty mainstream, I'm wondering if this approach is becoming more popular now for being more mobile and off-grid,,,?

Since small DC compressors have really come down in price, I can see how DC refrigerator/freezers become so much more convenient than having to buy ice and deal with the melted mess for any extended trip.

Thank you DARPA! Years ago, they put out a request for designs for a cooling system small enough to be wearable in battle. (Think back to the Desert Storm era), but quickly realized that it was a bad idea to deploy these in a hostile situation. NASA picked up the ball, and integrated the technology into space suits, and there were several other market uses that were found, like portable temperature controlled drug storage, and organ transportation, and as the market grew, the Chinese clones made them a cheaper commodity.

Ladies and gentlemen, I am happy to report that while I didn't get around to unloading the appliances from the minivan until this evening (wife and I were both zonked from the trip back), and had left it running both the refrigerator and the freezer (which needs defrosting now, too), it was only down to 43% capacity, which leads me to believe that I didn't start the trip with it fully charged in the first place.

I also found that my small DC solar badge bit submission was flagged incomplete, and really, I can't complain, because while many of you have been following along, the volunteer review staffers probably haven't and I really need to clean up the submission, so it looks more like a step-by-step journal of the build, which should make it much easier to judge it.

To be clear, no one is questioning my results, they continue to speak for themselves, but my documentation is lacking, so I will try to assemble something more coherent and methodical in a separate thread. It doesn't mean I will abandon this thread, at least not until Eric finishes his build 😉, but I really should post a separate and clear thread of my specific build.

Remember to be kind to the volunteer staff of this freely available platform!