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Chasing a ground loop

smithflys23

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.
 
N804RV said:
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.
Click to expand...

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.
 
smithflys23 said:
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.
Click to expand...

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?
 
BobTurner said:
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?
Click to expand...

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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rgodsy said:
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.
Click to expand...

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.
 
smithflys23 said:
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.
Click to expand...

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.
 
cbennet1 said:
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!
Click to expand...

I believe I checked this, but I will look again. Thank you
 
Mich48041 said:
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.
Click to expand...

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.
 
gasman said:
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.
Click to expand...

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?
 
BobTurner said:
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?
Click to expand...

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
 
AF_Alan said:
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
Click to expand...

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
 
AF_Alan said:
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
Click to expand...

Thanks, Alan.
 
AF_Alan said:
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
Click to expand...

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...
 
Hi !
I have a brand new RV8 and I have exactly the same problems:
Alternator noise in headset, varying with RPM
Strobe noise in headset, varying with RPM as well
Landing light noise in headset

When ALT is OFF there is no noise at all. A filter on the alternator does nothing.

I have all avionnics from Dynon and Aeroled lights. All the wiring has been done as per manufacturer instructions.

I've tried everything mentionned in this post but no change.

Did you find solutions ?
 
Antoine MTA said:
Hi !
I have a brand new RV8 and I have exactly the same problems:
Alternator noise in headset, varying with RPM
Strobe noise in headset, varying with RPM as well
Landing light noise in headset

When ALT is OFF there is no noise at all. A filter on the alternator does nothing.

I have all avionnics from Dynon and Aeroled lights. All the wiring has been done as per manufacturer instructions.

I've tried everything mentionned in this post but no change.

Did you find solutions ?
Click to expand...
I suggest these are two separate issues.

The LED strobe is RFI. The fix I did was to add a small aluminum backing plate on the NAV/Strobe. The NavStrobe gets a three #20 conductor shield cable. Conductors are:
- Nav power
- Strobe power
- Sync
- Ground is provided via the shield.

Note the photo:. The aluminum back plate on the inside of the wingtip connects the NAV/Strobe base to ground. Use the shortest lead from the NAV/Strobe ground wire to the backing plate, then connect the shield to the same point on the backing plate using one of the NAV/Strobe mount screws.

Do this, then reevaluate your other issues and let us know.

Note - the stock Landing Lights were replaced with a FlyLed units. No noise.

Carl
 

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I chased similar problems for several years. I pulled the alternator and had it bench checked. Checked OK. A year later, I partially disassembled it and found two stator wires broken at the attach screws, but arcing and still producing power. Had those broken but arcing wires repaired and no more noise. Just one man's experience.
 
Thanks for you replies !

More precisions :

I do have the forest of tabs connected to the firewall.

Yes I have the same for the strobe : 3 cond AWG20 shielded wire, NAV + STROBE + SYNC and the shield carry on the ground.

Same for landing light and taxi light with gauge 18.

Following this thread, I did mount aluminium plates into the wing tip connected to a wing rib. No change at all, however I only have a wire connected to the aluminium plate and wing rib, not to the shield that carry on the ground.

Maybe I'm wrong, but as I can hear alternator + strobe + landing and taxi lights + at a little degree the fuel boost pump, all of that ONLY when the alternator is ON, I was looking more in the side of the alternator or on the side of the radio / intercom rather than on the side of the strobe only.

I will ask a friend a spare alternator to see if the problem comes from there...

I was wondering if the problem could come from the intercom itself, first I disconnected the ground from the stick as the PTT goes through this common ground but no change again.
I've used the prefabricated wire from Dynon, so all the wiring to the intercom is as per their standard. And wiring to the radio or from the intercom to ground or headset is as per manufacturer recommandations. Headset jacks are all isolated from the aircraft and their ground all go to the intercom.

This afternoon I will do a test with radio OFF but intercom ON and vice versa to see if it could be the radio antenae picking up all electric interferences.

It's really frustrating to have a brand new aircraft, having taken care of the electric installation, and still having this noise 😖
 
Measure the AC voltage on the main power bus. It should be less than 0.5 volts.
Check for poor ground connections, especially battery and engine cable connections to the firewall.
Ground wires should NOT be connected to painted surfaces.
The engine mount should NOT be used for electrical grounding.
 
I have radio noise on my 8 as well with the AeroLED. I called them and the engineer told me there was a problem with this on early units. Mine odds affected, but it’s too late to get a warranty replacement. He said new lights are the only real fix but to cut the ground straps first. That helped but the noise is still there. I’m planning on buying new lights at Oshkosh. They are plug in replacements but have an internal change to reduce noise. Hopefully new ones fix the problem or I’m out over one AMU!
 
just use kiss principal, give it its own iceolated power supply, very small agm motorcycle battery, and put it on a charger at night, or buy two and have one on a charger ready to go.
This is the little tiny AGM battery I have in my 1969 BSA 441 Victor, and works great.

Dont ground it to the plane, ground it right to the AGM motorcycle battery, place a breaker and switch inline and keep the circuit completely iceolated from the plane.
 

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Ruready said:
just use kiss principal, give its own iceolated power supply, very small agm motorcycle battery 2 pounds, and put it on a charger at night, or buy two and have one on a charger ready to go.
Click to expand...
Well, the real kiss approach would be to not replace like with like; replace them (installation work required) with FlyLEDs or similar, where noise free resistors are used for current limiting instead of a noise generating pulse width modulation circuit.
 
oaklandaviator said:
I have radio noise on my 8 as well with the AeroLED. I called them and the engineer told me there was a problem with this on early units. Mine odds affected, but it’s too late to get a warranty replacement. He said new lights are the only real fix but to cut the ground straps first. That helped but the noise is still there. I’m planning on buying new lights at Oshkosh. They are plug in replacements but have an internal change to reduce noise. Hopefully new ones fix the problem or I’m out over one AMU!
Click to expand...

I had early AeroLeds with this issue.
I eventually solved it without getting new improved Aeroleds
Check this thread

AeroLEDs Grounding... Am I over thinking this?

I'm starting to install my new AeroLED Nav/Strobes on my not yet closed QB wings and wanted to see if I'm being too anal about grounding. For the grounds at the lights, the installation manual states to ground the 3 conductor cable shielding, the black wire from the light (NS 90) and the case of...
vansairforce.net vansairforce.net
 
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