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NEGATIVE Voltage!

Posted: Sat Jul 13, 2019 3:39 pm
by OLL
Hi All,

I am trying to diagnose/repair an M365 battery problem and I am out of my depth.

The scooter won't charge. When I plug the charger in, the BMS blinks RED four times, then stops - no more red, no blue, nothing. The charger has a steady green light.

The contact tabs on the battery all seem solid and sturdy, but I have not opened up the shrink wrap. The battery is 36V model NE1003-H.

When I check the battery voltage, the readout is NEGATIVE –14.66, even though it's connected red-red, black-black. The DIY videos all show low voltage as an issue, but I have not seen any with NEGATIVE voltage. I don't even know what negative voltage means.

What should/can I do to get this working again? I wish I could just buy an affordable (and authentic) battery pack and swap it out, but at >$100+, that seems wasteful.

Please help! Thanks

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Re: NEGATIVE Voltage!

Posted: Sat Jul 13, 2019 7:02 pm
by Ben J
It seems one or more of your battery cells are reversed polarity.
Its not at all common thing, I only encountered a few times with lead acid batteries what were being abused.
You probably have to cut open the pack and measure individual cell groups.

Come to think of it, Really 'dunno if lithiums can be reversed, at any rate lithiums are hazardous if they get out of balance.
Be careful.

Re: NEGATIVE Voltage!

Posted: Sat Jul 13, 2019 7:44 pm
by Freebird
Shouldn't the voltmeter be set to 200 if the expected voltage is higher than 20?

Re: NEGATIVE Voltage!

Posted: Sat Jul 13, 2019 8:38 pm
by jaysonjehsen
alternatively make sure the leads of the voltmeter are plugged into the voltmeter the right way as well- they could be reversed-- the black should be ground (GND) and red should be +V. I've never seen a battery pack go negative like that though, and yeah batteries can explode (see macbook, samsung note 7, etc), so be careful

Re: NEGATIVE Voltage!

Posted: Sun Jul 14, 2019 1:43 am
by Butch456
hi
was the scooter working ok before. If so then chances are something went wrong with battery.
Have you checked your meter to make sure working correctly.
It is difficult to repair the battery if you havent done it before. There are used batteries can buy reasonable and justmake sure output voltage is good.

Re: NEGATIVE Voltage!

Posted: Sun Jul 21, 2019 11:52 pm
by OLL
Thanks for the suggestions and advice. I'm going to blame it on the voltmeter and assume that I had the voltmeter leads plugged into the opposite sockets. It isn't labeled clearly. I know enough to know that battery repair is beyond my skill set - if this isn't evidence, I'm not sure what is! LOL.