Strange Battery problem

[TJS109]

Hi,
I have an old Panda 36V battery with what to me seems a strange problem. The battery is faulty and has very low capacity. When charging it only charges to 37.6V. The green light comes on the charger and the charger output measures 42 v when removed from the battery. The battery has an enable switch so the charger input is not directly connected to the battery output. I assume that a cell or bank of cells is not working but would like to know what is going on. I am not going to try to repair the battery unless it is something really simple just aiming to understand the problem.
it is not easy to measure the charger output directly when connected but can try this if it is relevant
Any ideas ?

 

[matthewslack]

Hi,
I have an old Panda 36V battery with what to me seems a strange problem. The battery is faulty and has very low capacity. When charging it only charges to 37.6V. The green light comes on the charger and the charger output measures 42 v when removed from the battery. The battery has an enable switch so the charger input is not directly connected to the battery output. I assume that a cell or bank of cells is not working but would like to know what is going on. I am not going to try to repair the battery unless it is something really simple just aiming to understand the problem.
it is not easy to measure the charger output directly when connected but can try this if it is relevant
Any ideas ?

42 minus 37.6 = 4.4, which is not far off 4.2, which is one fully charged cell group.

There is probably a damaged cell group, or corrosion forming a bypass of a cell group.

Low capacity is because with one fewer cell groups in series, the BMS sees low voltage threshold well before the remaining cell groups are really flat.

Only a look inside will properly answer the question, and with a damaged battery that is a risky procedure.

 

[Nealh]

An old 36v panda battery , how old ?

Likely it is either very out of balance or just knackered. Even if fully charged to 42v it can still be knackered due to cell ageing.

To gain a bit of knowledge the battery is unusable as it is so no reason not to open it up and investigate with some simple voltage checks of the cell groups, 10 cell readings would give an idea of the battery state and whether to recycle it for scrap or try to see if it can be coaxed in to life.

 

[TJS109]

Thanks for the ideas.
it looks like a damaged cell or cells.
It just about gets me into town and back so it is still useful and means I can leave it on the bike without worries.