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This video has certainly broadened my knowledge concerning LFP / LiFePO4. Over time this channel (An American firefighter) has made it into my personal “trustworthy” list. However I’m only a spectator as I'm old school with flooded acid batteries, but I have been considering my options for several years now. I do appreciate that lead acid batteries can also overheat and vent hydrogen. However, this was a very big bang, apparently from a careful domestic installation of LiFePO4🫤.

Replying in a new thread because the source posts are in the monster thread. TL;DR I don't have data. I do have a growing suspicion that I want to take steps to avoid provoking that into a problem. Also diagonal (anti-parallel) wiring will equally share current in two identical batteries, provided the lugs are identically crimped i.e. most likely, bought as pre-assembled lengths. I too had hoped current sharing would be implicit and automatic. I've had most of the parts around for too long and I'm now setting to installing them... and I'm re-thinking. 😞 I still agree that brief imbalance should cause parallel re-balancing when the load comes off. if heavy inverter load allows one batteries to discharge faster than others, sustaining this can put that battery at a lower voltage then when the load comes off, the lower battery may be offered >50A recharge current from the group. The BMS should shut down that charge, but then how soon will it come back? How often will it take a recharge overload? What's the risk of doing that repeatedly? if I got my battery bank into that state, would I know it had happened? What are the symptoms? How would I recover it? All unknown, and the only way to test it is likely to burn several hundred quid and still not give me good answers. Unless I open the pack and instrument it before abusing it. If I were making youtube vids of it, it might pay back... nah, not for me. It seems to me that the flatness of the LFP charge curve plateau and the low internal resistance conspire to make this more of an issue that it would be with LA parallel banks. You don't want to blast them with 5C charge, but they'll take it for a moment and nothing bad will happen; also the cell voltages increase to meet you the moment you start charging. For readers who didn't know, LFP must not be charged below about 0°C. Some Fogstar batteries (at least) have heaters to get around this. More info https://www.perplexity.ai/search/please-explain-briefly-the-min-S24MQonvRNKYeL.Q76TOXw , which says cold charging will shorten battery life and some folks recommend staying above 5°C. Previously I had worried that a battery in the group could get trapped in a differently-charged state by cold, they're all cold-ish and empty-ish, but some are warm enough to allow charge then you accidentally split the SoC by charging some what happens next? I don't want to find out the hard way. To avoid it: batteries closer to the baseplate are better for roll stability, and better for staying ~4°C over winter. Keeping temperature history for the tops and bottoms of the batteries should allow inference about possible temperatures inside. This should be enough to be sufficiently cautious about charging in a near-cold environment. If I want heater pads later, I can add them. Not as good as having them inside the battery between cells, but surely cheaper. If I had a shunt on each battery, instead of one on the whole bank, I could know what's going on all the time. Shunt and/or fuse on each battery is barely compatible with the diagonal (anti-parallel) bank wiring scheme anyway. Found https://arcomarine.com/products/arco-zeus-high-energy-alternator-regulator (I can't guess why Bluetooth is considered a feature not a liability, but it doesn't really matter. I'm not in their target market.) Also earlier, @dmr You're using the DC-DC to share charge with the engine starter? Both ways? You're charging the domestic directly from the alternator? What about the risk of load dump when the BMS freaks on you without giving notice to the Arco Zeus? In this setup I would imagine giving the Arco the low threshold (to reduce the alternator output early) and let the DC-DC top them off. You said "both batteries" which sounds like your domestic bank is only one LFP unit, of maybe 100Ah or 200Ah? Ah no, moving from domestic bank of one to two? I'm using "battery bank" or "battery group" to mean several consumer-packaged 12.8V 100Ah LFP batteries of 4 cells each, which I will parallel one way or another. There are 5x 12.8V 100Ah for the domestic bank I want balanced. The alternator will charge the engine battery as usual. I'll charge the domestic from that, by VSR and/or DC-DC depending on how it works out. This is my way to avoid the risk of load dumps, because the engine starter will never disconnect while the engine runs. I am less certain that shedding 150A of charge current won't cause a high transient voltage (over microseconds?) before the LA battery chemistry catches up... but the current alternator struggles to give 40A anyway. Problem for another day. What I had been doing, before the distraction of the 50-page thread, is writing Python to calculate current sharing (iteratively) in the 5-way diagonal scheme. I also wanted to know the effect of putting a current-clamp and/or fuse leg on each negative. This is incomplete, but early results (if not bugs) are telling me that diagonal wiring is no silver bullet and the larger the group the worse it gets. Consequently I'm already moving my thoughts to busbar or star connection, with equal length cable to each battery.