I just thought I'd pass this on since it was a mystery/problem that has only just now been resolved:
I have a 69 GCBC Citabria that started popping the over voltage relay intermittently about a year and a half ago. I could re-set it in flight by cycling the master but it was still aggrivating.
So I pulled the overvoltage relay off the firewall and had it bench tested and it worked properly every time. Then I pulled the voltage regulator and had them check that and they said it was good. Keep in mind this is all original equipment.
The guy I took it to is a pilot/plane owner and pretty knowlegeable and said he doubted if it was the alternator since they rarely cause any over voltage problems and that I should probably look for a bad ground. If that checked out he said he would still recommend replacing the over-voltage regulator since it was the old mechanical type and it could still be my problem even though it tested good off the plane.
I have a couple buddies that are pretty sharp on electronics so we did grounding checks and even ran additional ground wires to be sure. One of them even rode in the plane with me with a recording scope and leads running up through the firewall to try to find the problem. The altenator was putting out the required voltage and as luck would have it, didn't pop the relay on that flight.
The problem continued to get worse and seemed to be rpm related. If I flew at 2,000 rpm or less it seemed like I could keep it from popping the relay. But eventually it got to the point where I'd pop the relay just doing the 1,700 run-up mag check!
That was the last straw. I was ready to spend the $410 bucks on the new combined regulator & over voltage relay from Zeftronics but just for the heck of it I figured I'd pull the alternator and have it checked.
I took it into the same guy that checked my other components and he gave it a spin, watched it for a moment and said, "hmmm, your brushes might be shot". I asked him how he could tell. He said that if the brushes were rubbing properly it wouldn't spin for that long.
He also said it looked pretty oily and that's hard on them also. He told me to sit tight and they'd pull it apart and take a look. Fifteen minutes later they had replaced the brushes (which were half their original length) and polished the contact area on the armature. Total due, $30. Still, I could only pray this related to my problem.
That night I re-istalled the alternator, buttoned it up, rolled it out of the hangar and did run-up tests and NO popped relay! Then I did three take-offs at full power and still no problems. I flew again yesterday just to be sure I wasn't just lucky and it's still holding solid. And to think I was sooo close to spending all that money and it still wouldn't have solved the problem!
I guess the moral to this story is to get ALL components checked out regardless of what anyone advises. As everyone knows, intermittent problems are the worst, but if I had just pulled the alternator a year ago I'd have saved myself a lot of grief!
I know this was long winded but I hope this helps someone else out there.
-blue skies and grass strips-
I have a 69 GCBC Citabria that started popping the over voltage relay intermittently about a year and a half ago. I could re-set it in flight by cycling the master but it was still aggrivating.
So I pulled the overvoltage relay off the firewall and had it bench tested and it worked properly every time. Then I pulled the voltage regulator and had them check that and they said it was good. Keep in mind this is all original equipment.
The guy I took it to is a pilot/plane owner and pretty knowlegeable and said he doubted if it was the alternator since they rarely cause any over voltage problems and that I should probably look for a bad ground. If that checked out he said he would still recommend replacing the over-voltage regulator since it was the old mechanical type and it could still be my problem even though it tested good off the plane.
I have a couple buddies that are pretty sharp on electronics so we did grounding checks and even ran additional ground wires to be sure. One of them even rode in the plane with me with a recording scope and leads running up through the firewall to try to find the problem. The altenator was putting out the required voltage and as luck would have it, didn't pop the relay on that flight.
The problem continued to get worse and seemed to be rpm related. If I flew at 2,000 rpm or less it seemed like I could keep it from popping the relay. But eventually it got to the point where I'd pop the relay just doing the 1,700 run-up mag check!
That was the last straw. I was ready to spend the $410 bucks on the new combined regulator & over voltage relay from Zeftronics but just for the heck of it I figured I'd pull the alternator and have it checked.
I took it into the same guy that checked my other components and he gave it a spin, watched it for a moment and said, "hmmm, your brushes might be shot". I asked him how he could tell. He said that if the brushes were rubbing properly it wouldn't spin for that long.
He also said it looked pretty oily and that's hard on them also. He told me to sit tight and they'd pull it apart and take a look. Fifteen minutes later they had replaced the brushes (which were half their original length) and polished the contact area on the armature. Total due, $30. Still, I could only pray this related to my problem.
That night I re-istalled the alternator, buttoned it up, rolled it out of the hangar and did run-up tests and NO popped relay! Then I did three take-offs at full power and still no problems. I flew again yesterday just to be sure I wasn't just lucky and it's still holding solid. And to think I was sooo close to spending all that money and it still wouldn't have solved the problem!
I guess the moral to this story is to get ALL components checked out regardless of what anyone advises. As everyone knows, intermittent problems are the worst, but if I had just pulled the alternator a year ago I'd have saved myself a lot of grief!
I know this was long winded but I hope this helps someone else out there.
-blue skies and grass strips-