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Alternator Noise When Touching Metal Airframe Grounds

 
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PostPosted: Sat Jun 09, 2018 6:22 pm    Post subject: Alternator Noise When Touching Metal Airframe Grounds Reply with quote

I've always had various levels of alternator and strobe noise in my audio system, and have never been able to track down and eliminate the problem. Today I was flying lots of short hops in the warm weather, sweating more than usual, and I noticed an interesting clue.

The noise got much louder when I touched the metal part of the push/pull throttle control. So then I tried the mixture, and prop controls, same thing. Then I tried the ceiling-mounted aluminum elevator trim wheel (which doesn't connect to the engine, of course), same thing. Touching the screws that hold the instrument panel in place, or the aluminum air vent in the panel did not generate the noise. 
I'm not really sure where the circuit path is in this case. The headset only makes contact with me through insulators like the leather ear seal covers and the furry pad at the top. My shoes have rubber soles, and seat upholstery is the only other thing I'm in contact with.
Has anyone encountered this before, and figured out what was causing it? It almost reminds me of being able to make noise by pointing my fingers near the heated windshield of some old plane I flew once. Sort of a windshield theremin


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PostPosted: Mon Jun 11, 2018 5:45 pm    Post subject: Alternator Noise When Touching Metal Airframe Grounds Reply with quote

Thanks for your help Bob. It's a 4-place airplane with stereo panel-powered Lemo jacks, parallel two-plug jacks (all isolated from the airframe) and a PS Engineering PAR100EX audio panel/intercom. In the past I've played with the volume controls but didn't think to try it out on this most recent flight. In the past, the noise was reduced when I turned down the intercom volume level, or the local headset level on the Bose X.

On Sun, Jun 10, 2018 at 12:36 PM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
Quote:
At 09:21 PM 6/9/2018, you wrote:
Quote:
I've always had various levels of alternator and strobe noise in my audio system, and have never been able to track down and eliminate the problem. Today I was flying lots of short hops in the warm weather, sweating more than usual, and I noticed an interesting clue.

The noise got much louder when I touched the metal part of the push/pull throttle control. So then I tried the mixture, and prop controls, same thing. Then I tried the ceiling-mounted aluminum elevator trim wheel (which doesn't connect to the engine, of course), same thing. Touching the screws that hold the instrument panel in place, or the aluminum air vent in the panel did not generate the noise.Â

I'm not really sure where the circuit path is in this case. The headset only makes contact with me through insulators like the leather ear seal covers and the furry pad at the top. My shoes have rubber soles, and seat upholstery is the only other thing I'm in contact with.

Has anyone encountered this before, and figured out what was causing it? It almost reminds me of being able to make noise by pointing my fingers near the heated windshield of some old plane I flew once. Sort of a windshield theremin

   Have you run the traps on seeking to discover
   at what point noise is entering the system?
   What volume controls or switches have an
   effect on the noise you hear? What does
   your audio system look like? Stereo phones?



  Bob . . .


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Eric M. Jones



Joined: 10 Jan 2006
Posts: 559
Location: Massachusetts

PostPosted: Tue Jun 12, 2018 8:27 am    Post subject: Re: Alternator Noise When Touching Metal Airframe Grounds Reply with quote

Reposted from a few years ago, but this might help.

EDN of 23NOV1995 had an article entitled: "Assume nothing. Test everything." which was a small guide to troubleshooting philosophy (although aimed more at computers and high falutin designs but applicable to life in general).

He (Jack Ganssle) taught some critical elements of troubleshooting that have helped me over the years. Allow me to share some of them them with you:

1) EVERYTHING YOU KNOW IS WRONG. I.e. Assume nothing. Is it really connected like you think? Are your measuring instrument working? Etc. To facilitate this process-->

2) Keep a notebook of what you are doing, what you suspect, random suspicions, sketches, details, notes for later improvements, hard-to-read numbers, EVERYTHING. When you review your notebook the next day, important clues will often jump out.

3) Start with an organized workbench with all tools at the ready. What are you going to need to test assumptions?

4) Ask for help. Don't be shy! Anybody can help by listening to your explanation...where the obvious might jump out.... Asking experts is how you'll learn, even if they don't have the answer.

5) Use the Internet. Hardly a day goes by without someone asking me a question and I reply (or would like to reply) "Let me Google that for you".
Google has developed the ability to understand plain language questions. The value of searching the 'net cannot be overstated. And it will only get better.

6) Remember, most problems have simple answers. Think "Connectors" not Integrated Circuits. Think "Horses" not Zebras.

We can all add tips to this list. Keep a copy in your notebook.

I would also add my paper on "Dabbling with Electricity". It explains in detail why "pigtails" are a bad idea as well a generally why almost nobody knows what electrons really do.


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PostPosted: Tue Jun 12, 2018 12:02 pm    Post subject: Alternator Noise When Touching Metal Airframe Grounds Reply with quote

Yes, and also a gns430w and skyview system.

On June 12, 2018 15:39:16 "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com> wrote:
Quote:
At 08:44 PM 6/11/2018, you wrote:
Quote:
Thanks for your help Bob. It's a 4-place airplane with stereo panel-powered Lemo jacks, parallel two-plug jacks (all isolated from the airframe) and a PS Engineering PAR100EX audio panel/intercom. In the past I've played with the volume controls but didn't think to try it out on this most recent flight. In the past, the noise was reduced when I turned down the intercom volume level, or the local headset level on the Bose X.

Okay, the fact that intercom volume has
an effect suggests that the noise is getting
in upstream of the intercom. The "touch
sensitivity" is suggestive of a possible
poor or even floating ground in the
upstream wiring.

Downloaded the manual . . . do you have
the remotely controlled comm transceiver?





Bob . . .


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PostPosted: Wed Jun 13, 2018 12:31 pm    Post subject: Alternator Noise When Touching Metal Airframe Grounds Reply with quote

Thanks Bob, I'll try that early next week and report back. What I was calling alternator noise does rise and fall with engine RPM, and goes away when I pull the main alternator field CB.

On Tue, Jun 12, 2018 at 6:13 PM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
Quote:
At 03:01 PM 6/12/2018, you wrote:
Quote:
Yes, and also a gns430w and skyview system.

  Just for grins . . . try unplugging the
  data cable between the intercom/controll
  panel and the remote transceiver . . . and
  see if the noise is affected.

  Oh yeah, are you sure it's alternator whine . . .
  pitch rises and falls with engine rpm?



  Bob . . .


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PostPosted: Mon Jun 18, 2018 11:17 am    Post subject: Alternator Noise When Touching Metal Airframe Grounds Reply with quote

Thanks Bob and everyone, I'm back with new data, having returned to the airplane and flown it today.

Disregard what I said before about the volume- the noise is not impacted by the local headset volume or by the intercom volume, or the 430 volume. It seems to be not adjustable at all. It does not seem to be present when the engine is not running, but then again the alternator noise is the majority of the noise, and it would not be present with the engine off.


On Tue, Jun 12, 2018 at 6:13 PM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
Quote:
At 03:01 PM 6/12/2018, you wrote:
Quote:
Yes, and also a gns430w and skyview system.

  Just for grins . . . try unplugging the
  data cable between the intercom/controll
  panel and the remote transceiver . . . and
  see if the noise is affected.

  Oh yeah, are you sure it's alternator whine . . .
  pitch rises and falls with engine rpm?



  Bob . . .


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PostPosted: Tue Jun 19, 2018 4:39 am    Post subject: Alternator Noise When Touching Metal Airframe Grounds Reply with quote

Yes, ANR heAdsets powered by the airplane electrical system.

On June 18, 2018 16:57:36 "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com> wrote:
Quote:
At 02:16 PM 6/18/2018, you wrote:
Quote:
Thanks Bob and everyone, I'm back with new data, having returned to the airplane and flown it today.

Disregard what I said before about the volume- the noise is not impacted by the local headset volume or by the intercom volume, or the 430 volume. It seems to be not adjustable at all. It does not seem to be present when the engine is not running, but then again the alternator noise is the majority of the noise, and it would not be present with the engine off.

Are these headsets noise canceling? I.e. fitted with
electronics of some kind? I was looking for Bose X
Model info on the 'net with no success for the quick
look-see.



Bob . . .


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PostPosted: Tue Jun 19, 2018 6:38 am    Post subject: Alternator Noise When Touching Metal Airframe Grounds Reply with quote

Good suggestion, thanks. So far all 4 lemo sets are the same. I have a dual plug version of the same bose to try, and can do that and report back.

On June 19, 2018 09:10:19 "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com> wrote:
Quote:
At 07:37 AM 6/19/2018, you wrote:
Quote:
Yes, ANR heAdsets powered by the airplane electrical system.

Okay, do I correctly interpret that your
audio system is capable of using either
the Bose X or say a plain vanilla headset?

The fact that your noise is affected by
changes in body conduction suggests that the
stimulus is entering the system through
those spaces in close proximity to your
bod . . . like the things clamped on your
head?

Try another headset if you can . . .



Bob . . .


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PostPosted: Tue Jun 19, 2018 10:30 am    Post subject: Alternator Noise When Touching Metal Airframe Grounds Reply with quote

A lemo plug has mic and audio plus the power in one plug. These are not phone jack type plugs. The dual plugs are the typical phone jack with the audio and mic cables seperate, also no power.

On Tue, Jun 19, 2018, 11:12 Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

Quote:
At 09:36 AM 6/19/2018, you wrote:
Quote:
Good suggestion, thanks. So far all 4 lemo sets are the same. I have a dual plug version of the same bose to try, and can do that and report back

  Hmmmm . . . not sure I've got an accurate image
  of the differences between 'lemo' and 'dual plug'.
  Does this described the connectors at the end
  of the headset cord . . . single mulit-pin as opposed
  to "Y" plugs?

  To be significant, the test headset needs to
  be a generic, non-electronic . . . but go
  ahead and try the dual-plug Bose X too.



  Bob . . .


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PostPosted: Tue Jul 03, 2018 10:04 am    Post subject: Alternator Noise When Touching Metal Airframe Grounds Reply with quote

I've confirmed that the noise is present regardless of whether the ANR is on or off. I have not yet been able to round up a plain headset to try. My troubleshooting is a little slow at the moment because I'm only getting to the airplane once a week. If there is a floating ground somewhere in the audio system, are there any hints about where I might try looking for it?

I have another alternator to try, and hope to have time to do that on Friday.
On Tue, Jun 19, 2018 at 2:27 PM, Roger <rnjcurtis(at)charter.net (rnjcurtis(at)charter.net)> wrote:
Quote:

Is the noise still present when the ANR is turned off?
 
Roger

 
At 09:36 AM 6/19/2018, you wrote:

Quote:

Good suggestion, thanks. So far all 4 lemo sets are the same. I have a dual plug version of the same bose to try, and can do that and report back


  Hmmmm . . . not sure I've got an accurate image
  of the differences between 'lemo' and 'dual plug'.
  Does this described the connectors at the end
  of the headset cord . . . single mulit-pin as opposed
  to "Y" plugs?

  To be significant, the test headset needs to
  be a generic, non-electronic . . . but go
  ahead and try the dual-plug Bose X too.


  Bob . . .
 



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PostPosted: Mon Jul 16, 2018 6:44 pm    Post subject: Alternator Noise When Touching Metal Airframe Grounds Reply with quote

I got to spend more time today on the audio problem. I replaced the alternator, because I had a spare hanging around, and because it seemed like the old one wasn't working as well.

Before the swap, at idle RPM I would see something like 25 amps as it recharged the battery. Now I'm seeing 45 at the same RPM. Once the battery was topped up after the cranking and the alternator was back into its 10A range, the noise is gone. So it seems that I was only getting the noise when the alternator was working hard, but because the old alternator was always working hard, I was always getting the noise.
I'd still love to figure out how to fix the audio system so that it would not be victimized, but at least for now it seems like the antagonist is fixed.
On Tue, Jul 3, 2018 at 2:03 PM, Jared Yates <email(at)jaredyates.com (email(at)jaredyates.com)> wrote:
Quote:
I've confirmed that the noise is present regardless of whether the ANR is on or off. I have not yet been able to round up a plain headset to try. My troubleshooting is a little slow at the moment because I'm only getting to the airplane once a week. If there is a floating ground somewhere in the audio system, are there any hints about where I might try looking for it?

I have another alternator to try, and hope to have time to do that on Friday.
On Tue, Jun 19, 2018 at 2:27 PM, Roger <rnjcurtis(at)charter.net (rnjcurtis(at)charter.net)> wrote:
Quote:

Is the noise still present when the ANR is turned off?
 
Roger

 
At 09:36 AM 6/19/2018, you wrote:

Quote:

Good suggestion, thanks. So far all 4 lemo sets are the same. I have a dual plug version of the same bose to try, and can do that and report back


  Hmmmm . . . not sure I've got an accurate image
  of the differences between 'lemo' and 'dual plug'.
  Does this described the connectors at the end
  of the headset cord . . . single mulit-pin as opposed
  to "Y" plugs?

  To be significant, the test headset needs to
  be a generic, non-electronic . . . but go
  ahead and try the dual-plug Bose X too.


  Bob . . .
 






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