Bad BMS or bad design or what

Trying to get some traction on this: had a p group go bad and i cant tell why but would like some advice. Is there a bench test i can perform on the bms?


The story:
Had a pack i made lost a p group but I thought it was a cell problem so sent it to the bench and grabbed my recycle pack i made from spare cells. First pack died on the charger, then the second did the same. The first p group went to 0 volts after charging for about 6hrs . Im thinking it might be a bms problem. BMS a daly 40a 10s and the group that died is the exact same.

Is there a way to test the bms to see if it’s the problem? Could it just be bad luck? Bad build design? I have updated my design to be more conventional flexible pack type but wanted to try and get some cycles from it but oh well. Or did my bms kill it.

Test voltage of the battery before the bms. Test voltage after the bms. Test voltages across all balance leads.

Report back with data please


I see you @b264. How’s life? Heard you moved.

Worth the derail

1 Like

Is the 0-volt measurement from the BMS, or manually measured?
If manually measured, was it measured at the balance connector, or at the cells?

1 Like

Voltage at bms output: 36.2
Voltage at bms input/battery output: 36.2

Pin1/neg 4.03
Pin1/pin2 4.04
Pin2/pin3. 4.03
Pin3/pin4. 4.03
Pin4/pin5. 4.03
Pin5/pin6. 4.03
Pin6/pin7. 4.02
Pin8/pin9. 4.02
Pin9/pin10 4.01
Pin10/pos. 0.0

Same voltage at battery terminals as on the balance lead. I know p group 10 is dead dead and i can repair the pack but I can’t figure out a way to test the bms itself beyond just confirming that it is balanced well, and because of that I don’t trust the bms to not kill another pack. Fool me once and all that, that bms is trash.

Measurement was made at the the bms balance connector as well as directly on the pack. Its a dumb bms so no telemetry output

I’d toss it in the bin and use a different one from a different manufacturer.

1 Like

It was a Daly bms, so it’s not a complete unknown? I want to go with a smart bms.

what’s the current meta for a good 20a (charge only setup) bms? Reading around it looks like LTT is the only game in town and only if you buy direct but I hesitate because o dont have enough experience to know what’s best or even “good enough” as i have had so many failures. ( ive had two other no name bms’s fail in other ways)

I’m also unsure of the model to select so if you have a sec or have a good link to a how to thread it would be much appreciated.

What i need:

charge only 10s6p for a p42a pack

Charge only with CANbus out for a 12s9p P42a pack

ENNOID is great.
Much better, but much more expensive as well.

1 Like

The lite version looks pretty good. I cant find the balance current for the lite. If it’s the same as the larger version it’s almost perfect. I would rather pay half that but im not going to bitch if it keeps me from trashing batteries. Still haven’t found a good way to test a bms besides running with a test battery and just monitoring its performance… or I’ll just cry once

Thanks for shooting me in the right direction!


50mA balancing, perfectly adequate for any esk8 use case.