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I recently purchased an electric skateboard and I ended up having some issues with the board turning off as soon as it started to move.

I figured that there was an issue with the lithium ion pack so I removed it from the board so that I could test the pack with my multi-meter.

It is made up of 20 18650 3.7V 2000mAh lithium ion cells in as 10S2P configuration.

When I read the voltage of the pack at the XT60 connector it starts at about 8V and drops to 0V fairly quickly.

When I plug in the pack to the charger and measure the voltage at the XT60 connector it reads a constant 38.4V

But if I measure the voltage between all of the cells before the custom PCB that has the BMS and the lithium ion protection circuit it reads 40.4V

This makes me think there is an issue somewhere in the custom PCB and that the cells themselves are ok, but I'm unsure how to proceed to be able to use this pack as a functional electric skateboard battery pack.

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  • \$\begingroup\$ Please confirm, that it is 10S2P and not the other way round. \$\endgroup\$
    – Arsenal
    Jul 10, 2020 at 7:01
  • \$\begingroup\$ The protection circuit has both over charge and over discharge protection and should also have short circuit protection. It drives some chunky FETS. The BMS is probably broken. The 8v is leakage through the FETs. As the pack is neither over charged not over discharged the BMS should have turned both FETs on when you plugged the charger in. It is worth checking cell voltage when charger in. If charger is 38 but cells is 40 then the charge FET is off. We already know the discharge FET is off. \$\endgroup\$
    – Robin Iddon
    Jul 10, 2020 at 7:17
  • \$\begingroup\$ Maybe there is thermal regulation somewhere and it's got a broken wire so now the BMS thinks it is super cold or hot? \$\endgroup\$
    – Robin Iddon
    Jul 10, 2020 at 7:17
  • \$\begingroup\$ It is a 10S2P battery and not a 10P2S battery as I put in the original post, that has been updated. \$\endgroup\$
    – Alex Beebe
    Jul 10, 2020 at 20:48
  • \$\begingroup\$ I think you might be correct about a broken wire somewhere, if I apply pressure to the center of the pack the voltage jumps up to 38.5V but as soon as I remove the pressure it drops back down to 0V. I haven't been able to isolate the broken wire yet though. \$\endgroup\$
    – Alex Beebe
    Jul 10, 2020 at 20:49

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