Alternator Noise filter recommendation

[SixPapaCharlie]

So I decided to use the POA search feature and it led to some interesting discovery.

I can hear my alternator, landing lights, beacon, and strobes through my headset. Also my landing gear. when I raise and lower it, it rings loudly.
Well in searching POA, I saw someone recommend turning the alternator off and seeing what happens.

Yesterday while flying, I killed the alt in flight and everything went completely silent except the strobes.
It was awesome to have everything go quiet. I raised and lowered the gear and dead quiet.

Can someone recommend a good alternator noise filter? I see a variety at a wide range of prices. Anyone use a particular one and it fixes it or are they all pretty much the same?
Is it model specific?

Thx.

 

[bnt83]

So I decided to use the POA search feature and it led to some interesting discovery.

I can hear my alternator, landing lights, beacon, and strobes through my headset. Also my landing gear. when I raise and lower it, it rings loudly.
Well in searching POA, I saw someone recommend turning the alternator off and seeing what happens.

Yesterday while flying, I killed the alt in flight and everything went completely silent except the strobes.
It was awesome to have everything go quiet. I raised and lowered the gear and dead quiet.

Can someone recommend a good alternator noise filter? I see a variety at a wide range of prices. Anyone use a particular one and it fixes it or are they all pretty much the same?
Is it model specific?

Thx.

I have always wanted to play with Lone Star Aviation noise evaluator kits

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[Gary Ward]

How many hours are on the alternator?
I think I would have the alternator rebuilt and let them know about the noise your getting.

 

[Bell206]

I can hear my alternator, landing lights, beacon, and strobes through my headset. Also my landing gear. when I raise and lower it, it rings loudly.

Since you can hear all those separate items in your headset, it points to a ground/wire issue. Adding a filter may not do what you are looking for as they are more frequency dependent. Sounds more like a break in your ground path(s) which if repaired properly should give you silience without any filter.

 

[Clip4]

You may have a bunch of issues.

Licking Alternator Whine

Is that whine in your earphones driving you nuts? It might well be alternator-induced radio noise. Here's how to identify alternator and regulator noise, what causes it, and how to get rid of it.

www.avweb.com

 

[Will Kumley]

Since you can hear all those separate items in your headset, it points to a ground/wire issue. Adding a filter may not do what you are looking for as they are more frequency dependent. Sounds more like a break in your ground path(s) which if repaired properly should give you silience without any filter.

I was thinking the same thing. I can hear all kinds of things in my headset but its because before I owned the plane there was no ground block installed anywhere and all the grounds were haphazardly connected to various parts of the panel. While doing upgrades I've been fixing the grounds as I find them and hope to replace the radio soon with a newer radio which will also facilitate installing properly shielded and grounded wire for the headset and mic jacks.

 

[Dan Thomas]

See if the headset jacks have insulating washers to isolate them from the instrument panel. There are stray ground currents everywhere in airplanes, especially old airplanes, and you might be getting alternator ground flow through the panel, into the headset mike and audio ground, and then to ground at tha audio panel. Some of this gets into the amplification circuitry of the radios or audio panel. Those jacks need to be isolated first before chasing anything else.

 

[Capt. Geoffrey Thorpe]

See if the headset jacks have insulating washers to isolate them from the instrument panel. There are stray ground currents everywhere in airplanes, especially old airplanes, and you might be getting alternator ground flow through the panel, into the headset mike and audio ground, and then to ground at tha audio panel. Some of this gets into the amplification circuitry of the radios or audio panel. Those jacks need to be isolated first before chasing anything else.

You can say that again.

 

[Hang 4]

And be sure to check the rear ones too.

 

[Chip Sylverne]

Can you lay hands on an oscilloscope? Whine is often the result of a bad diode in the alternator. Looking at the trace off the main bus will tell the tale, if all pulses are the same amplitude the diode bridge is good, if they stairstep down one is bad. If the bridge is good, start checking grounds.

A filter is just a band-aid.

 

[eman1200]

have you tried the clapper?

 

[Jim K]

have you tried the clapper?


View attachment 129689

Have you tried antibiotics?

 

[Dan Thomas]

And be sure to check the rear ones too.

Yes.

And I should mention: If the jacks are not insulated from the airframe, they likely are using the airframe as the return path for the mike and audio. So once they're insulated, you need a dedicated ground wire from the jack to the radio rack ground. That's a pain for the rear jacks. If the wires are shielded, the shield might be enough to do the job without picking up more noise.

 

[Dan Thomas]

Can you lay hands on an oscilloscope? Whine is often the result of a bad diode in the alternator. Looking at the trace off the main bus will tell the tale, if all pulses are the same amplitude the diode bridge is good, if they stairstep down one is bad. If the bridge is good, start checking grounds.

A filter is just a band-aid.

Bad diodes are rare. I never encountered any. The OP is getting both alternator and strobe noise, suggesting that electrical ground loops are the problem, and most often grounded headset jacks are at fault.

 

[eman1200]

Have you tried antibiotics?

eh usually just some gojo and a brillo pad. the non-pumice one of course.

 

[Dan Thomas]

You may have a bunch of issues.

Licking Alternator Whine

Is that whine in your earphones driving you nuts? It might well be alternator-induced radio noise. Here's how to identify alternator and regulator noise, what causes it, and how to get rid of it.

www.avweb.com

That article misses the grounded-jack problem, and it also doesn't mention the alternator field circuit as a noisemaker. The field gets DC from the regulator, but inductive reactance from the stator coils induce a ripple in the field coil, and that noise can find its way into the bus as well. Cessna had a capacitor installed on some alternators, connected to the field terminal and grounded to the alternator case via the mounting clamp. IIRC, this was common in airplanes have an ADF installed, as alternator noise would cause the ADF to point where it shouldn't.

 

[iamtheari]

Yesterday while flying, I killed the alt in flight and everything went completely silent except the strobes.
It was awesome to have everything go quiet. I raised and lowered the gear and dead quiet.

Next time, turn off the magnetos. It'll be even quieter!

See if the headset jacks have insulating washers to isolate them from the instrument panel. There are stray ground currents everywhere in airplanes, especially old airplanes, and you might be getting alternator ground flow through the panel, into the headset mike and audio ground, and then to ground at tha audio panel. Some of this gets into the amplification circuitry of the radios or audio panel. Those jacks need to be isolated first before chasing anything else.

Definitely start here. Other than dropping the nuts and washers into the bowels of the airplane, this is a very easy first step and I agree it's a likely culprit.

How many hours are on the alternator?
I think I would have the alternator rebuilt and let them know about the noise your getting.

Also this. At least find out how old the alternator is from the logbooks. Depending on the logbooks, this might even be easier than checking the headset washers.