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Re: (ET) High current in reverse - E20

Finally got a warm day on the weekend to look into this. Found a couple bad connections on board #3 - one field resistor contact and one side of the varistor. Fixed those, but the problem perisisted. Finally found two bad diodes on board #4. These are the diode 'or' from the fwd and rev sides of the reversing contactors that provide the source voltage for the field circuit. This circuit had been repaired before (by PO) - traces fixed, new diodes. Oh yeah, and why the high current in reverse? The diodes were shorted, so I think that let the reverse supply voltage feed the field weakening circuit (normally fed only during fwd). So as throttle went up in reverse, the field would weaken (when it shoudn't) and along with the series field being reversed would not supply enough field - the motor spins up, current increases, voltage drops. Additionally the high current cut-out in the armature circuit only works in fwd (right?), so there would be no safety. That's my theory anyway. I also noticed I ran much faster (but weaker) in reverse, which, from reading recent postings, should not happen.
Anyway, any idea why would these diodes and/or traces fail? Could it have been the varistor being out of circuit? 

- SteveS
-E20
Lately, when I put my E20 in reverse, it seems to work ok until I get past the second 'step' on the throttle - then the power goes away, the voltmeter drops to 0, and I start to get that hot electric smell. I assume the field must be going open, but it never happens in forward. I need to break out the schematics, but thought I'd see if anyone has had this.
Just finished the first snow plowing of the winter - had to remember not to be smiling when my wife was watching ;-) 

SteveS
E20


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