Strange problem with my Bafang 750w ?

[KingKey]

I hope this is the right section for problem solving. I am having a problem with my Bafang motor. I'm unsure where the problem lays as the problem is a bit strange. If a turn on the LCD display it will not come on unless the charger cable is connected to the battery and the charger turned on.
If you disconnect the charger cable the LCD display turns off. I have disconnected the battery and held the LCD screen on button down to effectively do a 'reboot', then reconnected the battery but the problem still continues. The fan in the charger no longer runs when connected to the battery and the LED lights don't change ( now always 1 x red & 1 x green, was both red when charging ), so it doesn't indicate that it's charging. Can you give an idea what to look for or tests to run to diagnose which component is faulty?

 

[dustNbone]

Really sounds like a battery problem, specifically the BMS (Battery Management System). Can you use a multimeter to measure the output voltage (The plug that connects to the motor) without the charger connected?

It's possible that you have a bad cell group that's not holding enough voltage to prevent triggering the LVC (Low Volt Cutoff) which will cut power from the pack to the motor in order to prevent damage/fire.

It could also just be a loose/broken balance wire (the little ones that run from the BMS to each cell group). If you can access this wiring inside the battery give it a look and ensure they're all connected properly, also check each cell groups voltage (again without the charger connected) to make sure you don't have a cell group that's significantly lower (or higher) voltage than the rest. If all the cell voltages are within range, it's probably a bad BMS or wiring problem, if there's one group that's out of range then it's probably a cell gone bad and the BMS is doing it's job preventing catastrophe.

 

[KingKey]

Thanks for your advice. I have now opened the battery pack, disconnected the junction cable between the cells and the BMS. I've measured the voltage between each cell. They are all 4.16v to 4.17v which I guess is pretty good. So the problem could just be just the BMS unit. I'll email the supplier and see about getting a replacement and report back on progress.


EDIT:
I changed the BMS and that solved the problem.