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September 22, 2022

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Nico

I've never felt comfortable carrying a Li-Ion battery in my pocket or holding it in my hand.

Herb Glum

I purchased (12) 206 AH, 12V batteries for my home PV system, spending extra money (a little over $1,000 per battery) to get LiFePO4 batteries. The battery cells and BMS system are contained in a steel can that looks like an ammo can. That seems like a prudent design here in earthquake country. The Lithium Iron chemistry is well known to not exhibit the same fire risk as other chemistries and in fact they can be abused by overcharging, overheating, etc. and the battery cells won't catch fire. BUT, the electronics are another matter. My batteries are arranged in three series strings of 4 batteries, the three strings being paralleled. I checked with the battery manufacturer during the design of the system and they said that arrangement is fine for their batteries, just don't go over four batteries in series. I also checked with the inverter manufacturer and they also said their inverters will work well with that brand of battery and that configuration. The inverter parameters, including battery charge/discharge limits were set by the inverter manufacturer's tech support during installation. The entire installation was inspected, tested, inspected again, tested again and signed off. It was finally put into full time service eight months ago. Two months ago the inverters detected a fault and shut down the entire system. Kudos to the inverter manufacturer for monitoring everything in the system for any sort of abnormal operation. The problem was found to be two batteries in the same series string which were doing strange things, including intermittent open circuit, that couldn't be explained. The battery cans were opened and it was found that the BMS PC Board in each had suffered major heat damage. Components like the power switching semiconductors were melted into the heat sink and there was smoke everywhere inside the cans. Fortunately, the design is such that the BMS board is isolated from contact with the individual cells and, with the exception of 4 mounting screws, from contact with the can. There was no hint at all on the outside of the can that there had been overheating, not even any damage to the paint. The two toasted batteries were returned to the Mfr. for warranty replacement. The replacements were installed, the system inspected and tested and put back into operation. I have not heard anything from the Mfr. as to what caused the failure but having two failures out of the 12 that are in the system is very disconcerting. I'm really happy the fires didn't make it out of the cans.

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