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Current-based alternator noise

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rick(at)beebe.org
Guest

Posted: Sun May 09, 2021 1:03 pm Post subject: Current-based alternator noise

I have two alternators in       my plane. The original belt-driven one is 20 years old. I'm not       sure what exactly it is--the log book says it's an ESI 32B19549.       It's connected to a B&C LR3B voltage regulator. The second one       is a B&C BC410-H mounted on the accessory case with an SB1B-14       regulator.

       

       I get a horrid whine from the primary alternator. We discussed       that a few months ago and it was suggested I check the grounds. I       just finished my condition inspection and paid close attention to       all the grounding and it appears to be good. All connections are       tight with no corrosion. Measuring resistance from the alternator       case to the fuselage is only a few milliohms.

       

       The standby alternator is dead quiet.

       

       In flight, the whine isn't too horribly noticeable over the engine       noise except for when the strobes are on. Today I turned on the       pitot heat and the whine when from whoop whoop to a constant loud       whine. Normal draw, with strobes and landing light (which I always       leave on) is about 13 amps. If I shut off all the lights the draw       goes down to 11 amps and at that level the whine goes away. With       pitot heat on it's 19 amps and the whine is constant.

       

       Thoughts? Does it need to be rebuilt?

       

       Thanks.

       

       --Rick

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user9253

Joined: 28 Mar 2008
Posts: 1922
Location: Riley TWP Michigan

Posted: Sun May 09, 2021 3:31 pm Post subject: Re: Current-based alternator noise

Check the AC voltage. It should be less than 1 volt AC

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_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Sun May 09, 2021 4:27 pm Post subject: Current-based alternator noise

At 04:02 PM 5/9/2021, you wrote:

  	  Quote: 	
		   I have two alternators in my plane. The original belt-driven one is 20 years old. I'm not sure what exactly it is--the log book says it's an ESI 32B19549. It's connected to a B&C LR3B voltage regulator. The second one is a B&C BC410-H mounted on the accessory case with an SB1B-14 regulator.



 I get a horrid whine from the primary alternator. We discussed that a few months ago and it was suggested I check the grounds. I just finished my condition inspection and paid close attention to all the grounding and it appears to be good. All connections are tight with no corrosion. Measuring resistance from the alternator case to the fuselage is only a few milliohms.



 The standby alternator is dead quiet.



 In flight, the whine isn't too horribly noticeable over the engine noise except for when the strobes are on. Today I turned on the pitot heat and the whine when from whoop whoop to a constant loud whine. Normal draw, with strobes and landing light (which I always leave on) is about 13 amps. If I shut off all the lights the draw goes down to 11 amps and at that level the whine goes away. With pitot heat on it's 19 amps and the whine is constant.



 Thoughts? Does it need to be rebuilt?



 Thanks.



 --Rick 	


     99% of alternator noise issues do not

     arise from a failure in the alternator.

     The symptoms you describe are indicative

     of a ground loop in your audio system.



 

 

   Bob . . .



   Un impeachable logic: George Carlin asked, "If black boxes

   survive crashes, why don't they make the whole airplane

   out of that stuff?"

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nuckolls.bob(at)aeroelect
Guest

Posted: Sun May 09, 2021 4:37 pm Post subject: Current-based alternator noise

At 06:31 PM 5/9/2021, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>



 Check the AC voltage.  It should be less than 1 volt AC 	


   This check can be useful but it's not

   all inclusive particularly with digital

   voltohmeters that don't have an 'output'

   function (built in capacitor in series

   with the test lead).



   Also, digital voltmeters don't resolve

   AC to the native DC world as did analog

   meters. Mass of the pointers in analog

   meters produce an inertial averaging

   function. Digital meters won't read the

   same for the complex waveform that is 

   alternator ripple even if you add the

   requisite capacitor to take out the DC

   component. 



   This check goes to the possible but very rare

   instance of a bad diode in the alternator.

   Since this is a belt driven machine, one way

   to check it is take it off and have it run

   on a test bench at an alternator dealer or

   overhaul shop.



   An alternator with damaged diodes will not

   deliver anywhere near rated output current.



 



 

   Bob . . .



   Un impeachable logic: George Carlin asked, "If black boxes

   survive crashes, why don't they make the whole airplane

   out of that stuff?"

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skywagon185(at)gmail.com
Guest

Posted: Wed May 12, 2021 12:33 pm Post subject: Current-based alternator noise

Could be a power diode failure.



On Sun, May 9, 2021 at 2:05 PM Rick Beebe <rick(at)beebe.org (rick(at)beebe.org)> wrote:



 	  Quote: 	
		                      I have two alternators in       my plane. The original belt-driven one is 20 years old. I'm not       sure what exactly it is--the log book says it's an ESI 32B19549.       It's connected to a B&C LR3B voltage regulator. The second one       is a B&C BC410-H mounted on the accessory case with an SB1B-14       regulator.

       

       I get a horrid whine from the primary alternator. We discussed       that a few months ago and it was suggested I check the grounds. I       just finished my condition inspection and paid close attention to       all the grounding and it appears to be good. All connections are       tight with no corrosion. Measuring resistance from the alternator       case to the fuselage is only a few milliohms.

       

       The standby alternator is dead quiet.

       

       In flight, the whine isn't too horribly noticeable over the engine       noise except for when the strobes are on. Today I turned on the       pitot heat and the whine when from whoop whoop to a constant loud       whine. Normal draw, with strobes and landing light (which I always       leave on) is about 13 amps. If I shut off all the lights the draw       goes down to 11 amps and at that level the whine goes away. With       pitot heat on it's 19 amps and the whine is constant.

       

       Thoughts? Does it need to be rebuilt?

       

       Thanks.

       

       --Rick

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