Voltage to frame??

[JohnnieB]

Originally Posted by yurtle

Capacitive coupling?

Possible, but not likely. It is a DC system. The PWM output of the controller might capacitive couple to the frame, but it would only exist when the controller is passing amps to the motor.

Ohmic leakage currents have existed since people started building electrical gadgets, but we haven't had the instrumentation to detect them until recent times and they haven't caused operational problems until the input impedance on control circuits got so high that they react to a voltage from a high impedance source.

If the voltage on the frame is causing operational problems, two ways of fixing it come to mind.
1. Find the voltage leak to the frame and eliminate it.
2. Connect a resistor between the frame and the main negative terminal and eliminate the parasitic voltage.

[kgsc]

jb, would leaving a resistor from the neg pack main to the frame be a bad idea ?

[JohnnieB]

Originally Posted by kgsc

jb, would leaving a resistor from the neg pack main to the frame be a bad idea ?

It definitely wouldn't be my first choice, but if there is voltage on the frame; and the voltage source cannot be located; and the voltage on frame is causing operational issues; and the voltage goes away when a resistor is attached, I would consider semi-permanently install the highest Ohmic value resistor that would prevent the operational issues until I replaced whatever electronic device that wasn't working right.

A typical DVM's input impedance is 1-Meg, so I'd start with a 1-Meg resistor, which should halve the voltage on the frame and the controller might start acting normal.
If not, 500K
If not, 250K.
If not, 100K.
And so on until the controller started working right.

I wouldn't go below 1K due to the electrical safety issues.

Another possibility would be connecting a 1/4 Amp fast-blow fuse between the frame and battery pack negative. There would be a spark if you got a wrench or screwdriver between a battery positive and the frame, but the fuse ought to blow before the battery terminals started melting.

Of course, my first choice would be fixing the problem rather than treating the symptoms and possibly compromising the electrical safety.

[kgsc]

Agree on the safety part. Don't want an explosion that close to the boys

[TheFlash16]

Sorry guys! Forgot about this, but the controller had a short (somehow) and was leaking voltage to the frame. New controller and no voltage to the frame and ran great. Thanks again for all the help!!
Cameron