LiFePo4 Batteries Going Down, Reading -1V Spontaneously

[heraclite]

I’ve been having issues with my Tiny Home solar system where the whole thing will go down despite 1) plenty of power to charge, and 2) no low temp or low voltage I am aware of.

I have 8 x 12v 100ah Taico LiFePo4 batteries hooked to my 48V 3kW Growatt inverter, which charges off of 4 panels (~1200V). So there are two 48V “banks” of 4 batteries each connected to my inverter in parallel.

It worked fine for a while but has started going down every few days.

When the system goes down and I read all the batteries, all of them show good voltage except one in each bank will show -1V. I then need to jump them or hook them up to a charger to get them going again.

How is that possible? Are the BMSs defective perhaps? I don’t think there’s any way they’re getting overcharged. Though there was a month or two where they were left in the cold (not charging / discharging), so perhaps they could be damaged?

Any insight here would be *greatly* appreciated. Thanks.

 

[sunshine_eggo]

I’ve been having issues with my Tiny Home solar system where the whole thing will go down despite 1) plenty of power to charge, and 2) no low temp or low voltage I am aware of.

I have 8 x 12v 100ah Taico LiFePo4 batteries hooked to my 48V 3kW Growatt inverter, which charges off of 4 panels (~1200V). So there are two 48V “banks” of 4 batteries each connected to my inverter in parallel.

Did you individually charge each 12V to full and then parallel charge each group of 4 before putting them in series?

Do you periodically monitor them to ensure that all 12V in the string are at the same voltage when the inverter is at peak absorption voltage?

When the system goes down and I read all the batteries, all of them show good voltage except one in each bank will show -1V. I then need to jump them or hook them up to a charger to get them going again.

Sounds like BMS protection. I would presume this is happening following discharge and not charge.

How is that possible? Are the BMSs defective perhaps? I don’t think there’s any way they’re getting overcharged. Though there was a month or two where they were left in the cold, so perhaps they could be damaged?

Storage in the cold isn't a concern. Charging at or below freezing can destroy them.

Any insight here would be *greatly* appreciated. Thanks.

Due to hazmat regulations, batteries must ship at 30% SoC or lower. It's rare that they're all perfectly at the same state of charge, AND it's a miracle when the batteries are actually balanced internally. It's possible that the offending batteries are lower than the others, and they're tripping out early.