Can I charge this?

[djrobb]

Hi, this is one side of the battery pack from my 36v A2B ebike. I believe it was overly discharged from sitting. Can I charge this bank of batteries separately from the bike and its BMS?

I know I can disassemble it to the individual cells and test and charge them but I’m hoping to avoid that and slow charge it just like this. Thanks!

 

[fechter]

Yes, you could charge it assembled like that if you watch the voltages on the cell groups. Measure the voltages now. If the cells are below 2v or so, the cells are likely damaged and may be unsafe. That said, I've had some success with recovering over discharged cells by keeping the initial charge current very low until the cells are above 3v, then increasing the charge current.

If you have a single cell charger, you can charge each cell group individually until they are all up.

If the cells are really low to start with, there is an increased risk of them catching fire during charging. Charge in a fire safe location.

 

[djrobb]

Thank you very much. The charger I have is a 4 cell XTAR VC4. Should I get something else for this task or should i attach leads to one charging bay in this charger? I’m happy to invest in the “right” tool for this project.

XTAR VC4 Charger for Lithium-ion... https://www.amazon.com/dp/B010J9GE5G?ref=ppx_pop_mob_ap_share

 

[miro13car]

I think first you should recognize what is the connection combination of this subpack.
?S ?P
those cells are 4.2V fully charged, but what paraller, what series?
knowing connect combination will tell you what is terminal voltage fully charged,
you need this to figure out what to charge this subpack with.
I would use any plug in power supply, 9V, 12V , 32v ?? and watch individual voltages.

 

[fechter]

Thank you very much. The charger I have is a 4 cell XTAR VC4. Should I get something else for this task or should i attach leads to one charging bay in this charger? I’m happy to invest in the “right” tool for this project.

XTAR VC4 Charger for Lithium-ion... https://www.amazon.com/dp/B010J9GE5G?ref=ppx_pop_mob_ap_share

To use that one you would need a pair of alligator clip wires and you could only do one cell group at a time. I've used something like that in the past and it worked but was pretty slow. You can't use more than one "slot" in the charger at a time unless the cell groups were disconnected from each other.

Get some voltage measurements on the cells first.

 

[djrobb]

Thank you for your help. Each cell tested at 4.13 to 4.14 volts. Each of the two battery banks tested at 20.6 volts per bank. Does that mean they are full?

 

[fechter]

Thank you for your help. Each cell tested at 4.13 to 4.14 volts. Each of the two battery banks tested at 20.6 volts per bank. Does that mean they are full?

Yes. That's a good sign, sort of. Check the rest of your cells. If they are all in the same ballpark it means the cells are not over discharged but possibly the BMS went bad (or one of the sensing wires broke). Healthy range for that system is about 3.0v to 4.2v per cell.