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Alternator/Strobe whine

 
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PostPosted: Mon Sep 07, 2020 10:49 am    Post subject: Alternator/Strobe whine Reply with 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


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PostPosted: Mon Sep 07, 2020 1:46 pm    Post subject: Alternator/Strobe whine Reply with quote

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 shield grounds? Did you keep the strobe ground isolated from the local (at the strobe) airframe ground? Are your headphone & 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's 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. 
Charlie


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PostPosted: Mon Sep 07, 2020 6:35 pm    Post subject: Alternator/Strobe whine Reply with quote

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 shield grounds? Did you keep the strobe ground isolated from the local (at the strobe) airframe ground? Are your headphone & 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's 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. 


Charlie




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PostPosted: Tue Sep 08, 2020 6:13 am    Post subject: Re: Alternator/Strobe whine Reply with quote

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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PostPosted: Tue Sep 08, 2020 12:45 pm    Post subject: Alternator/Strobe whine Reply with 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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PostPosted: Tue Sep 08, 2020 1:07 pm    Post subject: Alternator/Strobe whine Reply with quote

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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PostPosted: Tue Sep 08, 2020 3:53 pm    Post subject: Alternator/Strobe whine Reply with quote

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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