Help tracking 72v short to chassis

GEM Forum
1

Hey community. While doing some testing, I found 72v (actually packV) on the chassis. Meter (black) was on B- on controller lug and (Red) was on chassis. Here’s my specs:

  • All pre-2004 harnesses, components, etc
  • Has the recall DC-DC upgrade
  • T2 controller
  • 72v Lithium
  • New rebuild and still in the testing phase. No prior working knowledge of all the components"

I needed to clean up all connections more thoroughly so, I started at the B+ stand off lug with the white wire:
Disconnected DC - 72v still on chassis
Disconnected Relay - 72v still on chassis
Disconnected Buzzer - 72v still on chassis
Disconnected 20pin IP - 72v still on chassis
When I disconnected the 23pin at controller, it went away.
So I’m assuming the short is downstream of the B+ at Pin 1 on the controller.

Any components known to cause this issue? Any guidance or wisdom is appreciated!
Thanks in advance!

2

Connect a 10k resistor from B- to chassis. Effectively across meter leads. Chassis is isolated, floating from traction battery.
If 10k brings it down it’s fine. A high impedance meter will measure static, phantom, voltage.
If you still have battery voltage with meter shunted by 10k, then continue your search.

3

@Inwo ok this makes sense. Im due for a new meter. I think klein makes one with built in low impedance? Prob easier to find than an actual resistor

4

That’s interesting, I did not know that, but the high impedance meters get lots of folk in trouble. They can read voltage by just touching the probes.

5

Yup. Klein model MM720. Its pricey but worth not having those headaches. Has 6k resistor built in and design for those “phantom” readings. Thanks again!