ebike battery wont turn on but will on charger

[4stroke]

Hi everyone,

Bought an electric bike, its a custom build from oxydrive, a samsung battery with a bafang 8fun 250w rear motor. The problem is when you put key in and turn it on, nothing happens but if you plug it in the charger it turns on and ride completely untill you switch it off from the same switch that wont turn it on. The battery is 36v with a usb on top of the charging port.

Anyone know what could it be ? Thanks

 

[AngryBob]

Likely a BMS problem. Contact vendor. DVM readings on battery, first turned off, turned on with no charger, then turned on with charger may yield definitive information.

 

[shane_da_bean]

also, try measuring voltage readings off of the balance connector, leave the ground probe of your voltmeter on the black cable then move the live probe along each of the other pins.

it should go up in equal gradients between each pin e.g a fully charged pack will read 4.2, 8.4, 12.6, etc. in 4.2 gradients (fully charged voltage of lithium cell) if the numbers fluctuate e.g. 4.2 8, 11.9 then there will be a problem with either the bms balancing or bad cells inside the pack.

count which number pin it is away from the ground wire, that has the change i.e 3.8v instead of 4.2v gradients like the rest. that would be the cell number with the problem.

Then open up the pack and count series connections on the cells starting from black until you get to the same number as the pins. (e.g cell 4 if it was the 4th pin from ground lead on balance wire that had issue)

the cells you end at are the ones that are different from the rest and most likely the problem, you can swap them out or rebuild the entire pack without them (less range).

 

[Balmorhea]

the cells you end at are the ones that are different from the rest and most likely the problem, you can swap them out or rebuild the entire pack without them (less range).

Don't forget that if you remove cells from the series, you'll need a different BMS and a different charger that terminates at the correct voltage for that number of cells.

It's better than throwing away an otherwise usable pack, but it's a pain in the butt.