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Isolation problem with battery pack

614 Views 1 Reply 2 Participants Last post by  Lowcoe
Hi Guys,

We're having a bit of an isolation headache on an EV we've retroffited with Li-ion.

A bit of background :
The pack is 106S divided in two 53S packs mounted on each side of a tubular frame not unlike this one :


Both packs are correctly isolated from the frame and so is the controller BUT when we measure the voltage from the battery + to the frame, we quickly find 300V and that slowly goes down from just the voltmeter impedance.
And as soon as the voltage is down, if we go to the battery - and do the same measurement to the frame, we find the same and that goes down.
Once discharged, the other side is "charged" and on and on...

We've read some literature like here http://www.tdipower.com/PDF/white_paper/Ground-Fault-White-Paper.pdf and it seems an accepted practice would be to have a 10Mohms resistor connected on each side (+ and -) of the battery pack and to the frame...
So far, we've tried our best to isolate the whole traction chain from the frame so we're a bit reluctant to connect it even through 10Mohms resistor but if that's a common practice then...

What's your take on this?

Thanks for your feedback!

Marc
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