2002 Gem e825 will not go forward or backwards

Each pack is its own autonomous unit. If one pack shuts off due to pop breaker or BMS disconnect, the whole vehicle shuts down.
Just like if you activated the main battery
Switch on The 6 in series lead batteries.
That big switch is a cut in the middle between a group of 3 lead batts in series.

It’s not that simple to engineer. Mosfets see the whole pack voltage. A normal 24v bms cannot be connected in a 72v system. They must use high voltage bms in each battery. Unless they use dry contacts.
Batteries can only balance locally unless communication between modules.
Resetting is an issue too. A tripped bms sees high voltage and might not reset easily.
It works, that’s the main thing. Doesn’t matter if I know how they did it. :slight_smile:

Yes, locally per pack. Each pack also has a volt meter display. Their claim is …
Up to 4 in series and 8 in parallel

If it was my Gem… I’d have one big 21s 20 or 40p one BMS …
But this is not mine and the person using it needed a drop in solution. These are designed as such.

I have a KWelder and 1000 Mod 3 2170 cells
Yes, just over 18kw. This will be my first cell lvl build although I’ve built pack lvl electric propulsion projects in the past series and paralleling lithium packs together. And a couple of 38120hp headway bus bar packs.

This video in my lithium lawn tractor conversion I’d did some years back with A123 LiFePO4 12.8v nominal 9.6ah packs.
I tested the packs and under a 5-7C rate 45-65 amps per pack… no voltage sag. :blush:


Good morning I know this post was quite a while ago but I had the same problem yesterday. Your symptoms are exactly what is happening with mine, which I believe is a 2000 GEM285. Do you still happen to have the schematic that you could share? My email is mpittj70@gmail.com. Any assistance you can provide is greatly appreciated