Introduction: Chinese Li-ion BMS Fix
My BMS for my powerwall had an annoying habit of latching off when the battery voltage dropped too low (usually overnight when the power was used up). It's meant to do this to protect the battery, but I had to switch the power to the batteries off and on again to get the charger to start charging the batteries the next day. It's a fairly standard 14S 48V chinese BMS that you can get for about £10 off eBay.
I have included a schematic of the type of BMS that I have used (I had the same issue with another BMS I used for my eBike). This is showing only 4 cells, but the extra cells are just stacked above and are identical circuits to cell 4. The first 3 cells are a bit different as you can see that the 3rd cell provides the bias voltage for the MOSFETs.
I found that adding a 100K ohm 'bleed' resistor (*R25 in schematic) across the charge/discharge port and the battery port allowed the circuit to self reset.
- Your BMS
- A 100K leaded resistor
- Heatshrink (optional)
Step 1: Fit Your Resistor!
Please refer to the images - I put heatshrink around my resistor, and it is at the bottom of the photo. Your BMS may be different, but a 100K resistor across these terminals should not do any damage as the current that can flow is tiny (500microamps at 50v). Just be sure you have the correct value first!