# BMS Voltage Output Question?

I’ve got a little issue that has be stumped I think I have a DOA BMS but need to sense check with everyone to make sure that’s the case please?

It’s a 10s3p pack and I have a 10s BMS attached to it. I’ve checked the balance wire configuration 4 times now and I just think it’s a dud!

At the battery terminals I’m getting 34.8v but out of the BMS I’m getting exactly half that! 17.4v!!!??

Any ideas anyone?

Does it have a e-switch? Try to put the charge in the bms and measure the voltage.

What BMS is that? Do you have a drawing of how you wired it?

This is the BMS.

No e-switch

I’ll try and get some charge to it but I don’t have a DC jack at the moment so I’ll have to improvise

Does not say much. try showing how you wired it. Have checked if between every two sequential balance wires you have ~3.48v and between the first wire and the third you have 2X3.48v and between the first and the 4th you have 3X3.48 and so?

It’s wired exactly like this… ie. The number balance wire etc.

I’ve checked each cell and they’re all the same voltage, and they all go up in the right increments as I go down the line.

I’m getting the full voltage when slapping the meter on the main pack’s + & - ends, but when the neg goes through the BMS it halves the voltage

Seems right. I’m almost sure iv’e seen this issue before. as I recall it was solved with a new BMS.

That’s my thinking… I think the BMS is kaput

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Isn’t B1 balance lead supposed to be the output from positive side of pack #1? Your first wire on your diagram looks like the first balance wire is B0 or B-

The markings on the BMS are B- (black, the only black, B1 in the diagram) all the way down the line to B+, which in this diagram is B11.

Yeah so your BMS requires 11 wires to fill in the balance leads for your 10S battery pack?

That’s usually not how bestech or supower BMS work. I don’t know about yours.

See a bestech BMS wiring below…

The first balance wire B1 is attached to the positive/negative between packs #1 & #2

This one seems different to that diagram…

This is the one I have. I actually forgot I was bypassing the BMS for discharge with this pack but I was still worried about the charging, until I found this diagram on the listing…

I was using P- whereas I should have been using C- !!!

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Ok you got a screwy wired BMS – I don’t like BMS’s that have that extra balance wire.

Now did you try and it maybe hard now but measure each progressive balance lead to see the voltage is increasing? See above what @Ishayc that technique.

then everything is good now?

Yes, when I use C- instead of P- for the neg discharge, all is good

Thanks for your help guys, I didn’t realise it was a weird BMS

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Have fun and ride safe

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