BMS Question

[d8veh]

I'm trying to repair a battery that has one cell much lower than the rest. Looking at the BMS, the positions for the bleed resistors and transistors are empty. I've seen a few BMSs like this. How do they balance the cells, or don't they?

The cost of those components would be nothing. Why do they leave them out?

 

[999zip999]

List the voltages of the cells of your battery
1. 3.25V
2. 3.33V
3. 2.80V
List them like these.
Tell about what type of battery lifepo4, liMin,lipo. ect.
Battery voltage,ah. Yes info.

 

[dnmun]

i also have seen those BMS without the balancing network. neither shunt transistor or resistors. they do not balance the pack. the cell that is out of balance will never get filled, you have to replace it with one that does have a a balancing network.

also the charger may shut off at the final voltage and not send out the balancing current so check that also.

the Modiary charger that cell-man sells is one of those which will not balance a lifepo4 pack because it turns off when it reaches final voltage.

 

[dmwahl]

Cost of the parts is low, but not nothing. In quantity it adds up. Chinese BMSs are hardly a market driven by quality and customer satisfaction.

I bought a cheap battery with BMS once that only shut off the pack for high voltage during charge but no balancing or LVC. I had the same symptoms you are having and took to just manually balancing the pack every 20-30 cycles. I would charge the pack until one cell hit HVC, then charge each cell with a single cell charger to bring them all up to full charge. Assuming no bad cells, that should at least buy you time to acquire a different BMS.

 

[d8veh]

i also have seen those BMS without the balancing network. neither shunt transistor or resistors. they do not balance the pack. the cell that is out of balance will never get filled, you have to replace it with one that does have a a balancing network.

also the charger may shut off at the final voltage and not send out the balancing current so check that also.

the Modiary charger that cell-man sells is one of those which will not balance a lifepo4 pack because it turns off when it reaches final voltage.

The highest cells were just over 4.2v, so it does appear that the charging only switches off when the pack high voltage has been reached, but what are all the other components for? They can't just be for cell LVC, surely?