Confused Noob with Interesting Standup Scooter Power Fault

retroject

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Dec 22, 2021
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Hello Everyone,
First post and I'm a bit of a noob, so sorry if this topic is covered somewhere else but I couldn't find anything while doing a search.
My 36v escooter fails to turn on - the display flashes momentarily and that is all. Assuming a battery issue, I measured each of the 12S LiFePo4 cells at 3.3v

So moving onto the BMS, which is an EMX-13002; I have B-, C- and P-, battery balance wires, and then an additional 3wire connector that goes up to the display/throttle. Red is B+, but the first question what are these wires for?
ATTACH]

Also I can't find the current cause of the fault, any ideas?

In way of extra information, if I disconnect the balance connector and the 3 wire connector I can measure 36v at P-, but trying to switch on, this drops to 18v before slowly coming back up to 36v. If I connect the 3wire connector and balance wires, P- is 20v.

I'm assuming it is a BMS error, but would like to confirm before spending money on replacements, so any help is appreciated.
 
And while it's hooked up that way, if it powers on "normally", then run the motor offground at full throttle while measuring the cells, to be sure they all still measure correctly while under a small load. Any that don't may be old or damaged, and be the cause of the problem (rather than the BMS).

Cells may read perfectly normal with no load, and then drop in voltage like a stone under load.


Also, there could simply be a wiring fault in the balance/sense leads/connector, most often a bad crimp or spread contact at the connector itself, sometimes a broken wire inside the insulation at the crimp or at the solder joint inside the pack.
 
The scooter powers up and runs normally when the BMS is bypassed, and thanks amberwolf, the cells measure fine while under full throttle.

So it looks like the BMS is cactus, thanks.
In regards to the three additional wires out from the BMS, I think they may be for a battery monitor on the display so you can see how much distance is left. Does anyone know a 12S LiFePo4 BMS with this additional plug, as I can't seem to find a replacement for the original.

Cheers and Merry Christmas to those who celebrate.
 
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