Help! BMS/Charger overcharges my 10s

Hey, so I finished my third build today.

I put the board on charge while finishing off the last pieces of the board. Thought it took long to charge and charger light never Went green. So I disconnect the charger and measure voltage from charge plug on the skateboard and it shows 44.5v. The bms is supposed to cut off after 42v and the charger supply 43.5 volt if measure it.

I used this setup last summer, same charger and same batterypack&bms and only thing and never noticed any problem.

I also dissembled the pack and measured from XT90 and was still to high. Im not sure but felt like voltage dropped abit over time. Went out and took a tour on the board and now the voltage is down to 40v again.

Any idea?


If your 10s charger output 43.5V than through it in the trash.

Idk what is wrong with your bms, but I would definitely measure the voltage of every p-pack now and look if one of the packs is out of the row.


Thanks for reply. Yeah gonna do that. But if one would be disconnected I feel like voltage would be lower and not higher since it balance.

Your charger shouldn’t charge over 42V in general. So even if your bms isn’t working the overall voltage of your battery shouldn’t exceed 42v as the charger would switch off by his own.

1 Like

Share a link to your charger so others can stay clear of it

What charger are you using? You can maybe open it and set the correct voltage with the potentiometer

@anon64938381 @pjotr47 @Andy87

Slight correction, missread the voltage, charger supply 42.3. I dont have a link but its a 2A 10s charger that say it supply 42.3 so thats correct. Its an ebike charger for li-ion 10s4p package. using samsung cells.

I just measured the voltage on bms after draining battery abit - None of the paralells differ any in voltage.

This is the bms

The adapter must give 42v not more!

@pjotr47 but how can the bms reach higher voltage than the charging supply supplies?