Alternator Noise

[NovaBandit]

I seem to have a bit of alternator whine from my PlanePower 60 amp alternator in my headsets. It is occurring whether or not the intercom or radios are active (I can hear it when nothing is breaking squelch). The whine goes away when I switch the alternator off.

Also, I have a PlanePower 30 amp vacuum pad mounted secondary alternator. When I switch to this alternator, at the same RPM, putting out the same amperage, I get NO whine. Both alternators have their own shunts and ANLs, but then are joined together after the shunts before connecting to the main power bus (before the firewall passthru even). The field wires for both alternators are fairly well separated from all other wiring.

My gut feeling is that the PlanePower 60 is just a noisy alternator, and I'm tempted to replace it with an externally regulated alternator at some time down the road. In the meantime, are there any tricks to reduce this noise?

 

[Paul K]

I recall the same thing about 20 hrs before my PP went toes up. Nothing conclusive but is the noise somthing new or has it always been there? May or may not be a warning of future problems but if so, perhaps a clue as to why these are failing after a relitively short life. It has been suggested that there may be an external condition causing these to fail.

 

[NovaBandit]

The engine/alternator both have about 20h SNEW. The whine has been there since day 1.

 

[kai]

There could be several issues leading to noise. Is 20hrs SNEW also the total airframe hours, or is this a replacement and the issue came with the unit?

1. Grounding problems can lead to alternator whining. Check your headset jack insulation washers, check proper grounding of the engine, battery and avionics ground.
2. A diode of the rectifier inside the alternator could have failed, this leads to ripples in the output voltage which causes noise
3. Try a filter like this: http://www.aircraftspruce.com/catalog/elpages/lsAlternatorfilter.php

I have one installed with the PP alternator and so far no noise...

Good luck!

 

[NovaBandit]

There could be several issues leading to noise. Is 20hrs SNEW also the total airframe hours, or is this a replacement and the issue came with the unit?

1. Grounding problems can lead to alternator whining. Check your headset jack insulation washers, check proper grounding of the engine, battery and avionics ground.
2. A diode of the rectifier inside the alternator could have failed, this leads to ripples in the output voltage which causes noise
3. Try a filter like this: http://www.aircraftspruce.com/catalog/elpages/lsAlternatorfilter.php

I have one installed with the PP alternator and so far no noise...

Good luck!

This is 20 SNEW on the entire airframe, engine, alternator... brand new plane.

I've verified that the headset jacks are all well insulated, all avionics run to a common grounding block (that itself is well grounded to the airframe), and the engine has a dedicated grounding strap. If it were an issue with grounding, wouldn't the secondary alternator cause the same issues?

Is there a way to test the rectifier in the alternator?

Is that "filter" just a capacitor? Seems like a simple enough thing to try.

 

[kai]

I've verified that the headset jacks are all well insulated, all avionics run to a common grounding block (that itself is well grounded to the airframe), and the engine has a dedicated grounding strap. If it were an issue with grounding, wouldn't the secondary alternator cause the same issues?

Not neccessarily, the "electronic gremlins" could cause strange things...
Your grounding sounds good to me and with only 20hrs SNEW there should be no corrosion on grounding contacts...

Is there a way to test the rectifier in the alternator?

You could use a scope and check the output voltage of the alternator and compare it your second one.

Is that "filter" just a capacitor? Seems like a simple enough thing to try.

I?m not sure if there is also a coil installed.
I would give it a try as this is an easy thing.

Our airplane had the same problem shortly after we bought it (150hrs). It was indeed a failed diode inside the alternator. We replaced it with a bigger one (60A).

Let us know the results.

 

[rleffler]

Ed,

I agree with Kai. Remember, it may not be a lack of ground, but too many. A single ground loop, especially with anything that is connected to your intercom has the capability of being RF impacted.

The problem is that ground loops are usually hard to pin point if it's causing an issue without a scope.

bob

 

[Raymo]

Give the folks at PlanePower a call and they will be happy to discuss with you any possible problems and resolutions. Very friendly the one time I called them.

 

[AltonD]

I had the whine on a new setup. It was the Plasma ignition causing it. I added a big fat Capacitor from B&C to the avionics bus and I have never heard it again.

 

[aerhed]

Try disconnecting the shunt wires on the front one. Isn't that the only divergent path? Also, how are the alternators grounded? Are both grounded through the engine and out through your strap?

 

[kai]

Did you fix that issue? If yes, what was it?