# Curtis 1221C Ground loop problem



## SolarJ (Sep 12, 2009)

Well, After searching over the entire truck. I thought the E-meter was giving me ground fault grief. But I completely removed it and someone had already put a DC to DC converter on it. The only thing remaining on the traction pack is the Curtis controller. With the non-isolated charger plugged in the body of the truck sits around 60VAC @ .6A "Danger here" You never want any of the traction pack attached to the 12V accessory battery + or -. I can ground the truck and remove it but that means if I plug into a GFI outlet it trips it. Plus it is sending current over the ground wire not the best idea.

Has anyone heard of the controller causing a ground loop between to traction battery - and the case of the controller? I guess I could isolate the controller case from the body of the truck.

Is there a failed capacitor or something touching the inside case maybe? 

Thanks, Jim


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## EVfun (Mar 14, 2010)

How about the motor? This is actually common on older motors that are full of brush dust to have a bit of a ground fault and it is pretty difficult to tell a controller ground fault from a motor ground fault so long as the two are connected. 

I find that with a dirty motor and a Curtis 1221B controller I can trip a GFI, and that things don't have to be nearly as dirty when the motor is liberally doused in rainwater.


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## Tesseract (Sep 27, 2008)

I'll second EVfun's recommendation to check the motor connections. More specifically, test this by disconnecting both cables going from the controller to the motor. If the ground fault goes away then you can conclude the problem is in the motor. This could be from brush dust, as EVfun suggested, or it could be a much more serious problem like a field winding making contact with the case (insulation melted or rubbed through).


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## SolarJ (Sep 12, 2009)

Thanks for the Info guys. I did find that the motor had about 800K Ohms from the brushes to the case. Any words on cleaning it up to remove the dust, maybe a pressure washer then dry it with a quick blowout with airgun and run around the block to heat it up?


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## Tesseract (Sep 27, 2008)

I would just use compressed air - no solvents of any kind, including water 

However, 800k won't allow enough current to flow to trip a GFCI - it usually takes ~5mA to trip one, and 800k will let ~0.15mA flow.

So the problem might actually be in the charger itself.

Still, it never hurts to blow the brush dust out of a dc motor, just don't douse it with some chemical (or water) which may not be compatible with the winding insulation.


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