Charge port voltage much lower than discharge connector voltage. Anyone ever experienced that?


Charge port voltage much lower than discharge connector voltage. Anyone ever experienced that?

Hi everyone :slight_smile:

I got this brand new Wowgo Sanyo battery, that I’ve had laying around for like 6 months and then recently, I finally went ahead and took a look at it.

Turns out the voltage over the charge port is NOT the same as over the discharge connector.

  • Charge port: 10V, sometimes like 15V. It’s confusing lol…
  • Discharge connector: 39V

I’ve checked all the P-groups voltage and they’re all 3,9V

I have checked for loose connections.

I’ve tried charging the battery for 15 minutes and it went fine. Charged the battery about 0,3V. All P-groups still balanced.
The voltage over the charge port with the charger connected was around 0,4V higher than over the discharge connector.

When I connect my battery-meter to the charge port, the voltage drops to like 1V and it can’t even power the battery meter.

I’ve got another battery from Wowgo (different model, could be same BMS though :thinking:) that works completely fine and where I’m actually able to connect a battery-meter lol.

My questions are: (no need to answer all of them :stuck_out_tongue_winking_eye: )

  • Have anyone ever experienced such thing?
  • Do you think the BMS is faulty?
  • Anyone knows where I can get a Wowgo BMS?
  • Maybe just small BMS recommendations?

I’m kinda split between either the BMS is faulty or it’s just a weird BMS that works fine.

Any help is appreciated :slight_smile:

Thanks for reading till the end and have a lovely day. Stay safe :slight_smile:

Does the BMS have separate ports for charging and discharging?
If yes is there anything else connected to C- additional to the charge port?

I recently had 2 cutoffs of my BMS where the output voltage afterwards was also very low (If I remember right also something like 10V). My BMS has charge and discharge on the same port so everything was affected. I unplugged everything from BMS and re-connected, afterwads voltage was normal again.

A week later during riding on heavy terrain the BMS cut off again. I just unplugged the voltage meter this time and tada the BMS worked again. So in my case it was a faulty cable of the voltage meter which sometimes shorted on heavy terrain. Everything good since then.

I would unplug everything from C- and measure voltage again, hope this helps!

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If I read your story about 6months lying around. I am thinking off a bms that goes into deep sleep mode. There are models who do that. Normally just plugging in a charger is more then enough to go to normal mode.

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The better BMSes will have separate switches for the charge and discharge port and enable and disable them accordingly.

I am guessing there is either a switch, ideal diode, or hardwired diode on the charge port, so it isn’t actually connect to the battery when you probe it with a multimeter.

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I enjoy living dangerously. Hook that bad boy up to a charger in a spot where it won’t catch anything else on fire if it goes. It shouldn’t go up, but it might.

If it charges, you are good. If it doesn’t, unplug it.


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Sure enough, I went ahead and sealed the battery up… Took some pictures though.

This is not my picture lol, but im 99% sure my battery got the same BMS just without the heat sink.

So yes, it has two different ports for charging and discharging.

And no, nothing else is connected to the charge port (not the discharge port either).


Will try to do that if I take off the heat shrink again :slight_smile: (Which I most likely will…) Thanks a lot for your input :slight_smile:

Hmm interesting. I’ve had it connected to a small amplifier with a step down converter about 3-4 months in the period of 6 months. Just for a few hours though.

I tried that, nothing exploded but didn’t work either :sweat_smile: Thanks a lot for the help though :slight_smile:

Hmm maybe. The negative charge wire goes from C- and that has nothing connected in between. Positive charge wire comes straight from + and nothing connected is in between as far as I know. There could be something on the PCB though :thinking:

I know the issue is over the negative charge wire, because I can measure the full voltage across positive charge wire and b-.

That makes total sense, since i’m just bypassing the bms lol and basically measuring the discharge connector.

Thanks for the comment :slight_smile:

Haha, I actually did that. It charged completely fine but still same crappy voltage over the charge port afterwards.

Thanks for your help :slight_smile: #yolo

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