yay electrical gremlins!

[sly dvl]

Re: yay electrical gremlins!

The rotor windings if loose will expand out on acceleration. This would cause an open condition or a short condition. An open condition would result in no load battery reading and a shorted winding will show a load condition. Hence the lower than battery at rest reading.The rotor is shorted.
Repairing alternators since 1964 I have seem this shorted condition only a few times.

What are the windings shorting against? Once they've shorted would they remain shorted?

 

[kentuc]

Re: yay electrical gremlins!

The windings short against each other. It`s called a short circuit! The field circuit would normally draw 3-4 amps, but when the windings short, the draw would be higher. It`s not necessarily a short to ground.

 

[sly dvl]

Re: yay electrical gremlins!

The windings short against each other.

But that's what I'm saying. Once this short condition has occured wouldn't the condition then always exist, regardless of RPM? It's not like the field windings are loosely wound and are allowed to shift at various RPM's.

 

[91blazins10]

Re: yay electrical gremlins!

Got it working right now :tup: , the scratches in the slip rings were it, it looked like the rotor was used and dropped and it put a dent in the slip rings also making a very uneven surface so the brushes were just skipping off. And fyi cs144's that come out of cadillacs have a different voltage regulator and it does not work with our trucks. I swapped that over because the brushes looked better, but thats when I had the strange voltage problem in the post above, swapped back to the other voltage regulator and all is fine, and now I can drive my truck.

 

[sly dvl]

Re: yay electrical gremlins!

Congrats! :tup:

 

[91blazins10]

Re: yay electrical gremlins!

Any chance of getting a pic or two put up of this damage? I'd like to see it. Part of the "exchange of knowledge" we all try to participate in here.
Thanks,
DP

yea ill take some tomorrow.

 

[91blazins10]

Re: yay electrical gremlins!

heres a picture of what I was talking about, this is after I sanded it down, but the scratches were still deep enough to cause problems.

 

[sly dvl]

Re: yay electrical gremlins!

And it's flattened out where the scratches are, creating a "ramp" when the brushes leave the damaged area.
This kind of problem is rare, but it does happen. Good find.