BMS shuts down when battery powered off

juhanik

1 µW
Joined
Jul 27, 2021
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1
I have a 48V, 17.5Ah battery with a on/off switch (from aliexpress: hailong case, should have samsung cells but obviously, no way to be sure they are genuine).

The other day, battery would not power the bike when switched on.
The output is about 19V when switched on.
I did basic troubleshooting and measured the cell group voltages. All 13 were at 4.1V so I think the cells are ok.

After I connected the balance harness, battery started working.
The weird thing is, every time I switch the battery off, the BMS shuts down. I must unplug the harness for a few second to get it working again. Jumpstarting with the charger does not seem to work.
I guess it is time to buy a new BMS.
(Or keep the battery always "on" but knowing there is something wrong with the BMS, this is not a nice option)

The current bms is this model:
http://www.best-way.cn/en/products/bwpb-509s.html
Does anyone know it this is a typical problem for this model? It would be tempting to buy the same model so that the existing balance harness connector is compatible.
 
juhanik said:
I have a 48V, 17.5Ah battery with a on/off switch. ... The other day, battery would not power the bike when switched on.The output is about 19V when switched on.

I did basic troubleshooting and measured the cell group voltages. All 13 were at 4.1V so I think the cells are ok.
So its a 13S 48V battery. Being all p-groups are 4.1V I'd disconnect/bypass the BMS and keep checking the p-group voltages after each discharge cycle and after each charge cycle. It does sound like the battery is aok, but a poor connection somewhere and/or in need of a new/better BMS.
 
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