BMS stopped working on UPS battery

[Halo.wings]

Hi Everyone,

I have a small UPS (APC 350) and it was working fine for a while (there were a few power outages but it worked and seemed to charge up with no issues).

Yesterday for no reason I heard a constant beep and the light to replace the batter was on. I pull the batter out and I can read a voltage of 7.6 V (which is lower than the 9.6V I would have expected). I hooked the battery up to my DC power supply to charge it and there is no current going into the battery.

I pulled the battery apart and checked the BMS board (model here - 3S-40A) - There is a little bit of heat damage behind the resisters (430 ohm) but nothing serious and a quick check says that the resistance is still correct on them. Other than that there is no damage to the board at all.

I have replaced it with a YIT-Elements BMS (3S 10A - YIT-Element) I have from another project and am recharging the battery now with my DC power supply.

I wanted to ask as the UPS keeps up a trickle charge at 14.0 V is this what is killing the BMS board or is it just a bad board and I should just order up 10 of them next time to be on the safe side?

The BMS board said it can have an input from 16.0V to 12.6V so I thought it would be safe to use this in the UPS setup but I am not sure it can handle the constant voltage (I assume the voltage is burned off via resisters on the BMS).

Are there BMS boards that are designed specifically for applications like this? I searched and did not find any.

 

[OffGridInTheCity]

There's nothing magical or special about the failed BMS - any BMS that can handle the cell type + max amps can be a replacement. The model was 3s-40a - e.g. likely means 3 cells in series @ 40a load maximum. 40a * 10v = 400w which makes sense for a 350w UPS.

I notice you say you replaced with 3s 10a - e.g. 10a? I'm guessing it's only 10a. 10a * 10v = 100w and will not work put more than 80-100w load on the UPS. I'd look for a 40a BMS.