Intermittent alternator dropout

[Phil Bridges]

I took up our 64 PA-30 yesterday to exercise it. Turning off the left alternator to check if the right picks up the load initially resulted in no output from the right alternator. However, turning the left alternator back on and then off again a couple of times results in the right alternator picking up the load. Is this likely caused by a sticking relay?

[N3322G]

Phil,

Possible but more likely an intermittent problem - ask me how i know

Suggest checking ground and all connections.

after several problems, I invested in the alternator inop light kit - wonderful.

[Zach Grant L1011jock]

What kind of alternator system do you have installed, InterAV (Alcor/Motorolla) or Plane Power?
-Zach

[Phil Bridges]

Zach,

We have InterAv alternators.

[Zach Grant L1011jock]

You probably have a faulty voltage regulator. It is allowing voltage excursions, and the overvolt relay then kicks it offline. To verify this, check the bus voltage with just that alternator on. If the voltage varies with rpm, it is definitely bad. Being you can get it to reset, I doubt it is a wiring problem.
Zach

[Paul Klouda]

Don't know if a single will exhibit the same symptoms as a twinkie, but my '64 PA24-250 with an InterAV system had an intermittent problem of the alternator dropping off line. Sooo, after a new battery (needed it anyway), new alternator, new voltage regulator we finally replaced the over voltage relay (the part my A/P suggested in the first place - LOL) the problem went away. Checking all connections especially grounds is very prudent! InterAV provided free postmortem testing and confirmed the OV relay was faulity. The Alternator and Regulator are now spares! ... and we have a new charging system to boot!

[Phil Bridges]

Thanks for the suggestions. The grounds and connections seem OK. We will check both the voltage regulator and the overvoltage relay next week and get back to the forum with what we find.

[Phil Bridges]

Right now the problem of the right alternator dropping out appears to be a bad toggle switch. We were going through the trouble -shooting procedure recommended by InterAv and found that, on one occasion, turning on the right alternator switch did not complete the circuit. We have ordered two new switches and will replace both alternator switches, then take another test flight to see if the problem still exists. Thanks for all the suggestions, and I will post more information if the problem is still there.

[Phil Bridges]

Looks like replacing the alternator toggle switches did the trick. The right one was bad in that it would intermittently fail to turn on the right alternator. We went ahead and replaced both switches. Thanks for everyone's suggestions.

[N3322G]

Phil,

Wow, that's a new one. Thanks for sharing.

[TurboPA30]

[Zach Grant L1011jock]

Robert,
I'm curious how you were able to install a Plane Power voltage regulator on an Interav STC'd system. The way I read the STC for the Interav, it doesn't allow just the installation of motorola alternators, but requires the entire Interav kit to be installed, thus going the other way is also verboten. I think you need to check on the legality of this install, unless you have some different info from either the FAA, Interav or Plane Power, in which case I would like to have that for future reference. Thanks.
Zach

[Brian Fogleman]

I have seen this problem on a comanche 250. Alternator would drop off line and come back for no apparent reason. Would work at start up, then quit, might not work at start up, then start working. Very hit and miss. Alternator was overhauled, other componets checked. (Plane power kit). After much effort and trying to break it down to the most simple of the simple with a test light, we ended up making a "test jumper" (preferably fused) to go around the breaker, with alligator clips. We jumped the bus, and the load side of the breaker(on the ground) and finally identified the breaker as the fault. It would carry some voltage, but not work properly. Was replaced, and all works properly. It was never shown to be tripped. It was an original breaker in a 59 model.

Prior to this breaker replacement, the alt light never worked, after new breaker install, alt light worked properly at very low rpm.

I hope this helps someone with similar problem.