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Alternator/Strobe whine

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rick(at)beebe.org
Guest

Posted: Mon Sep 07, 2020 10:49 am Post subject: Alternator/Strobe whine

I could use a little         help debugging this problem. A few months ago I complete a major         panel overhaul on my GlaStar basically using Z-12. The plane         came with a B&C L40 alternator with an LR-3 voltage         regulator. There's always been strobe noise in the headset. A         couple years ago I replaced the "old" Whelen strobes with         AeroFlash LED strobes and all new shielded wiring. I still had         noise but it wasn't bad.     

As part of this         overhaul, I added a B&C BC-410H accessory pad alternator and         SB1B-14 standby regulator. Since either alternator can handle         the worst-case load, there's no essential bus. For space reasons         I ended up relocating and almost entirely rewiring the LR-3. I         also totally replaced all the avionics including audio panel,         intercom, headset jacks and all associated wiring.

            

The problem--the         strobe noise is worse. But it's only present when the primary         alternator is on. On just battery or just standby alternator the         system is silent. Any thoughts on how to silence this little         demon?     

Thanks     

--Rick

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ceengland7(at)gmail.com
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Posted: Mon Sep 07, 2020 1:46 pm Post subject: Alternator/Strobe whine

On Mon, Sep 7, 2020 at 1:58 PM Rick Beebe <rick(at)beebe.org (rick(at)beebe.org)> wrote:



 	  Quote: 	
		                      

I could use a little         help debugging this problem. A few months ago I complete a major         panel overhaul on my GlaStar basically using Z-12. The plane         came with a B&C L40 alternator with an LR-3 voltage         regulator. There's always been strobe noise in the headset. A         couple years ago I replaced the "old" Whelen strobes with         AeroFlash LED strobes and all new shielded wiring. I still had         noise but it wasn't bad.     

As part of this         overhaul, I added a B&C BC-410H accessory pad alternator and         SB1B-14 standby regulator. Since either alternator can handle         the worst-case load, there's no essential bus. For space reasons         I ended up relocating and almost entirely rewiring the LR-3. I         also totally replaced all the avionics including audio panel,         intercom, headset jacks and all associated wiring.

            

The problem--the         strobe noise is worse. But it's only present when the primary         alternator is on. On just battery or just standby alternator the         system is silent. Any thoughts on how to silence this little         demon?     

Thanks     

--Rick

	
Hi Rick,



Where are the strobe wire shieldÂ grounds? Did you keep the strobe ground isolated from the local (at the strobe) airframe ground? Are your headphoneÂ & mic jacks isolated from the airframe, and grounded only at the intercom? I've had moderate luck using the old (new?) single point ground technique shown in 'the book'. Since this is an ongoing issue with two different kinds of strobes, if it were me, I'd look at running an isolated strobe ground back to battery negative, or as close as is practical. What you *don't* want is the strobe and your low level audio stuff sharing the same ground path back to the battery negative. If that happens, the audio equipment'sÂ power supply (and likely the audio signal itself) sees the 'ripple' of noise from the strobes.

It's conceivable that the old strobes were radiating into the radio's RF input, but I wouldn't have thought that the LED version would be as bad.

Last (probably should have been first), you say 'strobe noise', but say it stops when the alternator is off. That doesn't sound like strobe noise; it sounds like alternator noise. Is the sound there when the alternator is on, but the strobes are off? Is (was) it the 'woop, woop' sound as the strobe fires, or continuous whine, or static, or ??? Does it vary in pitch or volume with engine rpm?

If it's actually alternator noise, you probably still need to look at grounds. Make sure the alternator has a 'zero resistance' (clean) connection to the engine, and that the engine has a perfect, low impedance ground back to the battery negative (can be through a firewall ground stud, but that should go directly to the battery). If you're using the steel cage in the Glastar for ground, make sure that *all* ground terminations to the cage Battery location could be a factor; is it at the firewall or behind the luggage compartment?

If all the grounds truly are good (only way to know for sure, without specialized test gear, is to unbolt and examine the mating surfaces), and it really is alternator noise instead of strobe noise, you might have a bad diode or two in the alternator itself.Â 

Charlie

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rick(at)beebe.org
Guest

Posted: Mon Sep 07, 2020 6:35 pm Post subject: Alternator/Strobe whine

Thanks for the help. The strobe noise is the 'woop woop' sound.       It was much woopier with the Whelen strobes but it's clearly       happening when the strobes flash. And it does stop when the       strobes are off.

          

There are sort-of two ground points now. There's a terminal strip       in the forward cockpit that all the non-avionics stuff such as       lights are grounded to. The ground wire from the battery runs to a       large stud at one end of that terminal strip. There's another       large stud on the other end with a large wire going to the engine.       When I built the new panel I incorporated a DB-25 central ground       connector on the panel with redundant connections to that terminal       strip.      

The strobes are not grounded at the wingtip. I ran the wire back       to the grounding terminal strip. I guess it's safe to say the       strobe ground does share the audio ground back to the battery.     

That said, I suppose it could be alternator noise. The strobes do       cause a fairly significant current spike when they flash. Maybe       I'm really hearing the alternator working harder during those       moments.     

--Rick

          



          On 9/7/2020 5:41 PM, Charlie England       wrote:

     

      	  Quote: 	
		                Hi Rick,                    

           

           Where are             the strobe wire shieldÂ grounds? Did you keep the strobe             ground isolated from the local (at the strobe) airframe             ground? Are your headphoneÂ & mic jacks isolated from the             airframe, and grounded only at the intercom? I've had             moderate luck using the old (new?) single point ground             technique shown in 'the book'. Since this is an ongoing             issue with two different kinds of strobes, if it were me,             I'd look at running an isolated strobe ground back to             battery negative, or as close as is practical. What you             *don't* want is the strobe and your low level audio stuff             sharing the same ground path back to the battery negative.             If that happens, the audio equipment'sÂ power supply (and             likely the audio signal itself) sees the 'ripple' of noise             from the strobes.

           

           

           It's             conceivable that the old strobes were radiating into the             radio's RF input, but I wouldn't have thought that the LED             version would be as bad.

           

           

           Last             (probably should have been first), you say 'strobe noise',             but say it stops when the alternator is off. That doesn't             sound like strobe noise; it sounds like alternator noise. Is             the sound there when the alternator is on, but the strobes             are off? Is (was) it the 'woop, woop' sound as the strobe             fires, or continuous whine, or static, or ??? Does it vary             in pitch or volume with engine rpm?

           

           

           If it's             actually alternator noise, you probably still need to look             at grounds. Make sure the alternator has a 'zero resistance'             (clean) connection to the engine, and that the engine has a             perfect, low impedance ground back to the battery negative             (can be through a firewall ground stud, but that should go             directly to the battery). If you're using the steel cage in             the Glastar for ground, make sure that *all* ground             terminations to the cage Battery location could be a factor;             is it at the firewall or behind the luggage compartment?

           

           

           If all the             grounds truly are good (only way to know for sure, without             specialized test gear, is to unbolt and examine the mating             surfaces), and it really is alternator noise instead of             strobe noise, you might have a bad diode or two in the             alternator itself.Â 

           

           

           Charlie

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user9253

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

Posted: Tue Sep 08, 2020 6:13 am Post subject: Re: Alternator/Strobe whine

Try running power and ground to the strobes using a twisted pair of wires.

Increasing the main alternator "B" terminal wire size might help.

Make sure the main alternator terminals are clean and tight.

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_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Sep 08, 2020 12:45 pm Post subject: Alternator/Strobe whine

Alternator, strobe or both?



 Alternator whine is almost always a ground loop issue.

 Pitch of whine will go up and down with engine rpm.

 It often gets louder when alternator loads are highest

 like right after starting engine (recharging battery)

 and all loads turned on.



 Strobe whine pitches up and down in synchronization

 with flashes from the strobes and is generally of

 constant volume.



 Which one(s) disappear when appliance is OFF.

 Alternator, strobe or both?



 



 

   Bob . . .

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ceengland7(at)gmail.com
Guest

Posted: Tue Sep 08, 2020 1:07 pm Post subject: Alternator/Strobe whine

On 9/8/2020 3:41 PM, Robert L.       Nuckolls, III wrote:

     

      	  Quote: 	
		                Alternator, strobe or both?

         

         Alternator whine is almost always a ground loop issue.

         Pitch of whine will go up and down with engine rpm.

         It often gets louder when alternator loads are highest

         like right after starting engine (recharging battery)

         and all loads turned on.

         

         Strobe whine pitches up and down in synchronization

         with flashes from the strobes and is generally of

         constant volume.

         

         Which one(s) disappear when appliance is OFF.

         Alternator, strobe or both?

         

         

         

                

             Bob . . .            	
     I think he mentioned in his reply to me that it was the 'woop woop'     indicating it is a strobe sound, but he also said that it stops when     the main alternator is turned off. (?)

     	          		Virus-free. www.avast.com 		 	 [url=#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2] [/url]

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rick(at)beebe.org
Guest

Posted: Tue Sep 08, 2020 3:53 pm Post subject: Alternator/Strobe whine

I'll be back at the         plane on Saturday and I will do some controlled tests. The noise         pitch is definitely in sync with the strobes. When I turn the         main alternator off the noise goes away completely. My memory is         that it also goes away when I turn the strobes off (main         alternator on), but I'm not sure if there's a residual whine.     

--Rick

          On 9/8/2020 4:41 PM, Robert L.       Nuckolls, III wrote:

     

      	  Quote: 	
		                Alternator, strobe or both?

         

         Alternator whine is almost always a ground loop issue.

         Pitch of whine will go up and down with engine rpm.

         It often gets louder when alternator loads are highest

         like right after starting engine (recharging battery)

         and all loads turned on.

         

         Strobe whine pitches up and down in synchronization

         with flashes from the strobes and is generally of

         constant volume.

         

         Which one(s) disappear when appliance is OFF.

         Alternator, strobe or both?

         

         

         

                

             Bob . . .

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