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.