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Chasing a ground loop

smithflys23

Well Known Member
I have been plagued with strobe noise ever since my -8 was wired by one of the "pro's". I have Aeroled multi voltage nav/strobes. I recently rewired my strobes hoping to eliminate the pulsing I hear with the strobes on. I ran separate ground wires for each strobe and grounded them all at the same point, the main ground bus. I grounded the shields independently on the light frame, and at a single point on the main ground bus. This was per Aeroleds suggestions.
I still get the pulsing noise in my headset. Very frustrating after all the work to rewire them.

Some other clues I've picked up along the way. The noise is not present when running only on the battery, and while on the ground. Ill have to try this airborne by shutting off the alternator, but I don't think this will make a difference. The noise only comes through the intercom. The pulsing does seem to change frequency slightly based on engine RPM. I also get a slight hum when my smoke pump is turned on.

Can anyone offer suggestions on where to look next? Does this sound like an intercom problem? It appears at first glance that the intercom is grounded correctly. Your help is appreciated!
 
These gripes are difficult to troubleshoot without really digging into your electrical and avionics systems.

One easy thing to rule out is your electrical system. You say it's most noticeable when you're flying. Have you ever done a bonding test on your electrical system's ground leg? If the ground leg from the negative post of your battery isn't doing its job, that can set you up for problems. You may also notice other problems like your starter doesn't turn over as fast as your friends airplane with the same set up.

Likewise, if you use the "forrest of tabs" type grounding system aft of the firewall, you need to make sure your grounding strip is likewise bonded. Under test conditions, you need to have less than 2.5 mili-ohms. And, a regular ohm meter won't do it, it has to be a bonding meter.

Another thing, one I'm sure youre already aware of, is that all your audio "common" wires have to be electrically "common" with the audio ground of your audio panel/intercom. And, they're not supposed to be grounded on the same "forrest of tabs" grounding strip your power circuits are grounded to.

This is all I can think of without knowing more about your airplane. I hope it helps.
 
These gripes are difficult to troubleshoot without really digging into your electrical and avionics systems.

One easy thing to rule out is your electrical system. You say it's most noticeable when you're flying. Have you ever done a bonding test on your electrical system's ground leg? If the ground leg from the negative post of your battery isn't doing its job, that can set you up for problems. You may also notice other problems like your starter doesn't turn over as fast as your friends airplane with the same set up.

Likewise, if you use the "forrest of tabs" type grounding system aft of the firewall, you need to make sure your grounding strip is likewise bonded. Under test conditions, you need to have less than 2.5 mili-ohms. And, a regular ohm meter won't do it, it has to be a bonding meter.

Another thing, one I'm sure youre already aware of, is that all your audio "common" wires have to be electrically "common" with the audio ground of your audio panel/intercom. And, they're not supposed to be grounded on the same "forrest of tabs" grounding strip your power circuits are grounded to.

This is all I can think of without knowing more about your airplane. I hope it helps.

Thanks for the reply, Ken.
I’m new to tracking down electrical gremlins, so The things you mention are things I know little about. I can certainly do some research in an effort to educate myself.

I have not done a bonding test. I’ll have to research this.

The battery appears to be grounded to the battery box frame.

I do have a forest of tabs behind the firewall.

I’ll also have to research the audio comm wires and electrically common.

One thing I forgot to mention, is that I have a VPX. I don’t know if that in any way changes things.
 
I ran separate ground wires for each strobe and grounded them all at the same point, the main ground bus.

The noise is not present when running only on the battery, and while on the ground.

Are the separate ground wires mentioned above running along side the power wires, both inside a shielded cable? Despite the manufacturer's instructions I would only ground the shield at the firewall, not the other end.

Are you saying there is no noise when on the ground, with the alternator and strobes running?
 
Are the separate ground wires mentioned above running along side the power wires, both inside a shielded cable? Despite the manufacturer's instructions I would only ground the shield at the firewall, not the other end.

Are you saying there is no noise when on the ground, with the alternator and strobes running?

Thanks for the reply, Bob.

The strobes are grounded with a separate unshielded wire running to each light. It runs along side the shielded 3 conductor wire that powers the lights.

FWIW, the grounding scheme came direct from their head electrical engineer. He said this way the shield would act as an actual shield. I simply followed his advice.

On the ground with the engine off, and running on the battery only, there is no noise when the strobes flash.

I’m going to see If the noise is present with the engine running and the alternator off.
 
Make sure all of your audio line shields are grounded on one side only. This includes your headset. Prevents noise that gets in an avionics unit from using the audio ground/shield as a path/loop.
 
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Make sure all of your audio line shields are grounded on one side only. This includes your headset. Prevents noise that gets in an avionics unit from using the audio ground/shield as a path/loop.

Thanks. I’ll take a look at that.
 
Strobes

Make sure your intercom jacks are physically isolated from the panel or wherever they are mounted assuming it is conductive. Insulated shoulder washer and flat washers on all jacks.

Lots of other great suggestions already posted. Good luck!
 
The strobe negative and positive power wires should be a twisted pair.
Try running the negative strobe wire all of the way to the alternator mounting bracket.
If nothing else solves the problem, try increasing the alternator "B" lead wire size.
 
Thanks for the reply, Ken.
I’m new to tracking down electrical gremlins, so The things you mention are things I know little about. I can certainly do some research in an effort to educate myself.

I have not done a bonding test. I’ll have to research this.

The battery appears to be grounded to the battery box frame.

I do have a forest of tabs behind the firewall.

I’ll also have to research the audio comm wires and electrically common.

One thing I forgot to mention, is that I have a VPX. I don’t know if that in any way changes things.

I would not consider this a good ground location. The full load of the starter must pass through the battery box bolts.

The forest of tabs should be bolted to the firewall with a passthrough brass bolt. The battery ground should connect to the brass bolt on the engine side. And a ground strap should go from the same bolt, to the engine case.
 
Make sure your intercom jacks are physically isolated from the panel or wherever they are mounted assuming it is conductive. Insulated shoulder washer and flat washers on all jacks.

Lots of other great suggestions already posted. Good luck!

I believe I checked this, but I will look again. Thank you
 
The strobe negative and positive power wires should be a twisted pair.
Try running the negative strobe wire all of the way to the alternator mounting bracket.
If nothing else solves the problem, try increasing the alternator "B" lead wire size.

These are Aeroled nav/strobes, so there are 3 wires. Power for the nav, power for the strobe, a sync, and a ground.

I’ll have to look into the B lead. I think this connects to the VPX.
 
I would not consider this a good ground location. The full load of the starter must pass through the battery box bolts.

The forest of tabs should be bolted to the firewall with a passthrough brass bolt. The battery ground should connect to the brass bolt on the engine side. And a ground strap should go from the same bolt, to the engine case.

When I saw how the battery was grounded, I thought this may be an issue.

The forest of tabs is as you describe. Although it’s on the panel aft of the actual firewall. I’ll have to see what is involved in running a new ground for the battery.
 
Before I flew today, I did another quick test.
With the engine running, and the alternator off, the noise disappears. Alternator on, it returns.
 
Typical ground loop issue.
1. Make certain alternator has a good, corrosion free ground path to firewall/forest of tabs. Check alternator, engine ground straps.
2. Make certain every connection to or from the intercom is floated (insulated) from the airframe (e.g., do not use the airframe for completing any connections). Fiber washers at and inside the holes for all jacks. I have seen CD players which work noise free when run on internal batteries but pick up a lot of alternator whine when plugged into a cigar lighter (completing the ground loop).
What brand intercom/audio panel are you using?
 
Typical ground loop issue.
1. Make certain alternator has a good, corrosion free ground path to firewall/forest of tabs. Check alternator, engine ground straps.
2. Make certain every connection to or from the intercom is floated (insulated) from the airframe (e.g., do not use the airframe for completing any connections). Fiber washers at and inside the holes for all jacks. I have seen CD players which work noise free when run on internal batteries but pick up a lot of alternator whine when plugged into a cigar lighter (completing the ground loop).
What brand intercom/audio panel are you using?

Bob, thanks again!

I’m going to have to take a look at what I’ve got under the cowling. As this conversation has evolved, I’ve been become more suspicious of some of the big ticket items. IE, the alternator, engine grounding, and battery wiring. I suspect this is where the issue is originating. This is especially frustrating considering I paid a substantial sum to have everything wired by a “pro”. I’ve been chasing nuisance problems for some time now.

I don’t think there is any corrosion due to the relative young age of my airplane.

Everything I have is recent manufacture Dynon, with the exception of my Garmin G5 back up instrument.
 
Here is an update to our audio noise.
While "reracking" the center stack radios, checking for pin condition and treating with corrosion protection, the back rectangular connector assembly of the Garmin GMA 340 audio panel tray was found (visually) with all screws loose. This is where shields and grounds are terminated and this seems to have been the problem for a long time. The speaker and headphones do not have the alternator whine any more. We won't list all of the other components replaced, tested and grounds cleaned, phone jack and aux audio input jack insulators checked etc.
Whewww!
 
I believe my connections are good, but definitely something to check.
I think I’ve got a battery or engine grounding issue that I need to address.
 
Similar setup, same issue, no solution

Been chasing the same problem and have tried all the suggestions above over last 7 years (560 hours). Dynon skyview with a G5, sl-30 radio, ps intercom, and aeroleds. Louder at higher RPMs and goes away completely if I turn off alt, or strobes, or intercom.

Rewired sections, added filter to leds, checked all ground paths...still haven't found the cause. Sorry I don't have a solution but it became hardly noticeable after the first 100 hours
 
Been chasing the same problem and have tried all the suggestions above over last 7 years (560 hours). Dynon skyview with a G5, sl-30 radio, ps intercom, and aeroleds. Louder at higher RPMs and goes away completely if I turn off alt, or strobes, or intercom.

Rewired sections, added filter to leds, checked all ground paths...still haven't found the cause. Sorry I don't have a solution but it became hardly noticeable after the first 100 hours

How is your battery grounded?
Do you have the multi voltage Aeroleds? Allegedly they are “noisier” that the single voltage. Aeroled offers an upgrade program for these lights.
 
Grounded per plans

I bought the Van's FWF kit and followed their plans. Battery to firewall with #2 (I think) cable, braided cable and #2 firewall to engine block, field of tabs for all neutrals on subpanel.

Build was completed in 2013 and I believe the aeroleds are single voltage but not certain.

Good luck
 
I bought the Van's FWF kit and followed their plans. Battery to firewall with #2 (I think) cable, braided cable and #2 firewall to engine block, field of tabs for all neutrals on subpanel.

Build was completed in 2013 and I believe the aeroleds are single voltage but not certain.

Good luck

Thanks, Alan.
 
I bought the Van's FWF kit and followed their plans. Battery to firewall with #2 (I think) cable, braided cable and #2 firewall to engine block, field of tabs for all neutrals on subpanel.

Build was completed in 2013 and I believe the aeroleds are single voltage but not certain.

Good luck

If they are from 2013 they are multi-voltage. The single voltage units have linear current regulations so they cannot generate any high frequency noise...
 
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