Alternator noise

[Dorfie]

Over the last few months I have a whine in my headphones coming from an alternator. This is new. For 600+ hours the alternators were quiet. It started a few months ago, Initially the whine was only from main alternator (PlanePower 60A) and only after startup when charging high amps (about 50-60 amps for couple of minutes, then decreasing, EarthX battery). It would go away as amps got lower. It was also only heard on No. 2 radio initially (GNC 255), and only from main alternator. Backup alternator (B+C 40A) was quiet when switched to backup. Overt time the whine has gotten louder and constant and now whines all the way to maintenance charging rate, does same on both alternators and now on both radios (GTN 750). Both alternator off and whine goes away.

Last week I removed main alternator and installed a brand new PlanePower alternator that I had. This made no difference in the noise, still on both radios as well as backup alternator. Looking at the diodes on the removed alternator there was nothing suspicious.

The engine is well grounded (I have 4 grounding straps), starter turns engine vigorously. All lights and avionics grounding come together at a single point as designed by Stein Air. No recent changes done to wiring. Both alternators charge as expected with amps changing as load is applied and voltage stable at 14.3-14.4V. The whine is clearly RPM related with pitch increasing as RPM increases. All alternator related contacts are secure. Both alternators now whine at idle RPM.

Where do I go from here?
Thank you.
Johan

 

[kms001]

Over the last few months I have a whine in my headphones coming from an alternator. This is new. For 600+ hours the alternators were quiet. It started a few months ago, Initially the whine was only from main alternator (PlanePower 60A) and only after startup when charging high amps (about 50-60 amps for couple of minutes, then decreasing, EarthX battery). It would go away as amps got lower. It was also only heard on No. 2 radio initially (GNC 255), and only from main alternator. Backup alternator (B+C 40A) was quiet when switched to backup. Overt time the whine has gotten louder and constant and now whines all the way to maintenance charging rate, does same on both alternators and now on both radios (GTN 750). Both alternator off and whine goes away.

Last week I removed main alternator and installed a brand new PlanePower alternator that I had. This made no difference in the noise, still on both radios as well as backup alternator. Looking at the diodes on the removed alternator there was nothing suspicious.

The engine is well grounded (I have 4 grounding straps), starter turns engine vigorously. All lights and avionics grounding come together at a single point as designed by Stein Air. No recent changes done to wiring. Both alternators charge as expected with amps changing as load is applied and voltage stable at 14.3-14.4V. The whine is clearly RPM related with pitch increasing as RPM increases. All alternator related contacts are secure. Both alternators now whine at idle RPM.

Where do I go from here?
Thank you.
Johan

If it's affecting both alternators now, and you have proved that the PP Alt is okay, I would suspect a deteriorating ground connection. Do you have a drawing of the primary power earthing arrangement? Or did you use BN Z series?

 

[bjdecker]

What's the specific mfg/model of Standby and Primary Alternator?

Can you connect an oscilloscope to the main buss and characterize the AC ripple riding on top of the DC -- what's the frequency, amplitude (volts) of the ripple?

 

[Avanza]

I would check the battery ground connector as the battery should absorb most of the AC ripple.
If no luck, I would install a 10,000 uF capacitor between avionics bus and GND.

Good luck

 

[MarkCFI]

I had an issue like this and it turned out to be the battery ground connection as stated above.

V/R

 

[Fred.Stucklen]

Over the last few months I have a whine in my headphones coming from an alternator. This is new. For 600+ hours the alternators were quiet. It started a few months ago, Initially the whine was only from main alternator (PlanePower 60A) and only after startup when charging high amps (about 50-60 amps for couple of minutes, then decreasing, EarthX battery). It would go away as amps got lower. It was also only heard on No. 2 radio initially (GNC 255), and only from main alternator. Backup alternator (B+C 40A) was quiet when switched to backup. Overt time the whine has gotten louder and constant and now whines all the way to maintenance charging rate, does same on both alternators and now on both radios (GTN 750). Both alternator off and whine goes away.

Last week I removed main alternator and installed a brand new PlanePower alternator that I had. This made no difference in the noise, still on both radios as well as backup alternator. Looking at the diodes on the removed alternator there was nothing suspicious.

The engine is well grounded (I have 4 grounding straps), starter turns engine vigorously. All lights and avionics grounding come together at a single point as designed by Stein Air. No recent changes done to wiring. Both alternators charge as expected with amps changing as load is applied and voltage stable at 14.3-14.4V. The whine is clearly RPM related with pitch increasing as RPM increases. All alternator related contacts are secure. Both alternators now whine at idle RPM.

Where do I go from here?
Thank you.
Johan

I would check to see if both/all headset jacks AND microphone jacks are isolated from the air frame. These circuits should only be grounded at a common avionics ground point, usually through the audio panel, or the radio grounds.

 

[Janekom]

I know this RV and owner well. A very meticulously built RV and with the main harness supplied by Stein Air. Initially we thought that it might come from one of the alternators because it has sound like a typical diode block failure whine - as described the OP.

The swop of alternators obviously now rules this out.

I would check to see if both/all headset jacks AND microphone jacks are isolated from the air frame. These circuits should only be grounded at a common avionics ground point, usually through the audio panel, or the radio grounds.

As far as I know it has been like that from day one.

It may be good to test on the ground with a good old school battery in place of the Earth-X. Then I would also go through all engine ground, battery ground ad the main alternator to battery wire terminals. Take them oof and clean them - there might be oxidation something. Also pull on the crimps. I have seen crimps deteriorate over years to the point where I could pull it out quite easily and there was evidence of a bad contact once pulled out.

Holding thumbs Dorfie

 

[ShawnR]

I suspect that all alternators whine. We usually find a way of preventing it from entering our headsets via the grounding (as mentioned), shielding (still part of the grounding) but, also, sometimes emi filters.

https://www.aircraftspruce.ca/catalog/elpages/lsAlternatorfilter.php?clickkey=22747

Since this was ok, but is now a concern "Over the last few months I have a whine in my headphones coming from an alternator. ", I wonder if there is a filter installed on one of the power lines or in the system that might be decaying...? Since it was one alternator, then both, and has increased to affect both headsets, it appears it is in a common connection.

Good luck! You could try the filter listed above, but if it works, it is a bandaid to correct the base fault, imho. Talk to Plane Power and see if they have filters built into their equipment that might be failing. But, again, since it was only one alternator (the larger of the 2) and only under heavier loads (generally creating more emi ), and is now on the smaller system too, I lean to a filter somewhere failing.

Looking forward to what you find!

 

[kms001]

Over the last few months I have a whine in my headphones coming from an alternator. This is new. For 600+ hours the alternators were quiet. It started a few months ago, Initially the whine was only from main alternator (PlanePower 60A) and only after startup when charging high amps (about 50-60 amps for couple of minutes, then decreasing, EarthX battery). It would go away as amps got lower. It was also only heard on No. 2 radio initially (GNC 255), and only from main alternator. Backup alternator (B+C 40A) was quiet when switched to backup. Overt time the whine has gotten louder and constant and now whines all the way to maintenance charging rate, does same on both alternators and now on both radios (GTN 750). Both alternator off and whine goes away.

Last week I removed main alternator and installed a brand new PlanePower alternator that I had. This made no difference in the noise, still on both radios as well as backup alternator. Looking at the diodes on the removed alternator there was nothing suspicious.

The engine is well grounded (I have 4 grounding straps), starter turns engine vigorously. All lights and avionics grounding come together at a single point as designed by Stein Air. No recent changes done to wiring. Both alternators charge as expected with amps changing as load is applied and voltage stable at 14.3-14.4V. The whine is clearly RPM related with pitch increasing as RPM increases. All alternator related contacts are secure. Both alternators now whine at idle RPM.

Where do I go from here?
Thank you.
Johan

Did the grounding check out okay? I would definitely be checking that before spending $150 on a capacitor (filter)

 

[Dorfie]

If it's affecting both alternators now, and you have proved that the PP Alt is okay, I would suspect a deteriorating ground connection. Do you have a drawing of the primary power earthing arrangement? Or did you use BN Z series?

I don't have a drawing of the earthing arrangement, but I can describe it. ALL of the grounding, avionics, lights etc come together at forest of tabs on the side of the GTN tray. There are many tabs. A large gauge wire runs from there back to the batt (-)ve. The battery is grounded to airframe locally at the battery. As mentioned, it has been quiet for the past 7 years. I do not know what BN Z series is.

What's the specific mfg/model of Standby and Primary Alternator?

Can you connect an oscilloscope to the main buss and characterize the AC ripple riding on top of the DC -- what's the frequency, amplitude (volts) of the ripple?

Stanby alternator is an externally regulated B&C 40 amp alternator mounted to accessory case. Regulator is LR3C. I do not have an oscilloscope. I will look into that and report back if I find one.

I would check the battery ground connector as the battery should absorb most of the AC ripple.
If no luck, I would install a 10,000 uF capacitor between avionics bus and GND.

Good luck

I had an issue like this and it turned out to be the battery ground connection as stated above.

V/R

Multiple people suggested fault at battery ground. Last night I checked all the connections related to the battery. They all appeared in mint condition. Nothing loose nor corroded.

I would check to see if both/all headset jacks AND microphone jacks are isolated from the air frame. These circuits should only be grounded at a common avionics ground point, usually through the audio panel, or the radio grounds.

I will check all the headphone plugs. I had all of that open during the CI completed this month, but I did not specifically look at each phone jack. The noise started before the CI, just much louder now.

I know this RV and owner well. A very meticulously built RV and with the main harness supplied by Stein Air. Initially we thought that it might come from one of the alternators because it has sound like a typical diode block failure whine - as described the OP.

The swop of alternators obviously now rules this out.


As far as I know it has been like that from day one.

It may be good to test on the ground with a good old school battery in place of the Earth-X. Then I would also go through all engine ground, battery ground ad the main alternator to battery wire terminals. Take them oof and clean them - there might be oxidation something. Also pull on the crimps. I have seen crimps deteriorate over years to the point where I could pull it out quite easily and there was evidence of a bad contact once pulled out.

Holding thumbs Dorfie

When I installed the new alternator that B-lead connector was clean. I have not removed the backup alternator connector but from outside it looks clean. Engine compartment is clean. I have pulled on the crimps.

Thank you for all the replies.
I must just mention that I have the VPX as circuit breakers. Not sure if that can contribute to the noise.
Johan

 

[Dorfie]

Did the grounding check out okay? I would definitely be checking that before spending $150 on a capacitor (filter)

I have not checked ALL of the grounding. Hopefully this weekend. I have checked all connections related to the battery and both alternators without any faults found. I was hoping it will be an easy fix!!!
Johan

 

[kms001]

I don't have a drawing of the earthing arrangement, but I can describe it. ALL of the grounding, avionics, lights etc come together at forest of tabs on the side of the GTN tray. There are many tabs. A large gauge wire runs from there back to the batt (-)ve. The battery is grounded to airframe locally at the battery. As mentioned, it has been quiet for the past 7 years. I do not know what BN Z series is.

Stanby alternator is an externally regulated B&C 40 amp alternator mounted to accessory case. Regulator is LR3C. I do not have an oscilloscope. I will look into that and report back if I find one.


Multiple people suggested fault at battery ground. Last night I checked all the connections related to the battery. They all appeared in mint condition. Nothing loose nor corroded.

I will check all the headphone plugs. I had all of that open during the CI completed this month, but I did not specifically look at each phone jack. The noise started before the CI, just much louder now.

When I installed the new alternator that B-lead connector was clean. I have not removed the backup alternator connector but from outside it looks clean. Engine compartment is clean. I have pulled on the crimps.

Thank you for all the replies.
I must just mention that I have the VPX as circuit breakers. Not sure if that can contribute to the noise.
Johan

It's the battery ground that's important.
Thanks
K

 

[Dr_Dave_MT]

It's the battery ground that's important.
Thanks
K

The B+ side is also important. Check those and the cable lugs. Was tinned copper wire used? Are you in a high humidity environment? An oscilloscope is your friend on this.

 

[Norman CYYJ]

The B+ side is also important. Check those and the cable lugs. Was tinned copper wire used? Are you in a high humidity environment? An oscilloscope is your friend on this.

Your connections to ground may appear tight and look good BUT can still be faulty. Remove and clean them and reinstall. Might very well cure your problem.

 

[Dr_Dave_MT]

Your connections to ground may appear tight and look good BUT can still be faulty. Remove and clean them and reinstall. Might very well cure your problem.

Years and years ago freezing under a POS car on the side of the highway, in a snowstorm, (yes, in my bare feet facing uphill both ways) I was cleaning a ground wire connection, doing an adolescent half-assed job. My Dad said quietly: “Do you want to be doing this again?”

This stuff sticks with me some 50 years later, credit him with some of my mechanical OCD?

 

[vlittle]

Any resistance in the alternator field wire can cause the whine and be alternator independent. Usually this is a bad switch or connection.

 

[Roadjunkie1]

It's the battery ground that's important.
Thanks
K

But also make sure the shielding on any shielded wire/cable is still grounded. Seems to be a place that occasionally breaks and a place that usually gets ignored as there are other BIG FISH that are checked out first..........

 

[Dorfie]

Thank you for all the replies and pointers.

Past weekend I removed all the engine to airframe ground straps. Even though there was no visible dirt or corrosion visible, I cleaned them all. The lugs are copper covered with Tin, as described earlier in this thread. Same was done at the battery connections. I also removed the right hand G3X screen which gives access to all the ground wires on the side of the GTN 750 tray. No issues observed. Tugged on every wire. After engine start the whine was still there, just as before.

I went through all switches on and off, adjusting the volume on both radios did not change the whine at all, even with volumes completely turned down it remained unchanged.

THEN I checked the volume on the audio-panel. Changing intercom volume had no effect. I have PMA9000EX audio-panel, an older audio-panel no longer produced. On the right side is a volume knob for music, and when I turned that down (which should have been turned to zero but somehow was not anymore), the whine went away, as in completely away, just like it has always been. I have not used that volume knob ever since I cancelled my XM music subscription about 2 years ago! At least now I can fly in alternator silence. But now I also wonder how the alternator noise gets into that output??

About 2 years ago I swopped the MFD (GDU 465) with the PFD (GDU 460) to get XM-weather in front of me. (I had issues with reliable BT connection for ADSB to GDU 460 PFD). The GDU 465 screen has Satellite receiver built in, and the music was hard wired to the audio-panel while that screen was on the right. I obviously lost that audio connection when I swopped the screens, but did not change any wiring. There was no alternator noise while I was using the XM music back then. Now, I wonder, what can cause the alternator noise getting into the audio output of the audio-panel??

Seems like it never stops!!

Thank you.

Johan

 

[bjdecker]

Thank you for all the replies and pointers.

Past weekend I removed all the engine to airframe ground straps. Even though there was no visible dirt or corrosion visible, I cleaned them all. The lugs are copper covered with Tin, as described earlier in this thread. Same was done at the battery connections. I also removed the right hand G3X screen which gives access to all the ground wires on the side of the GTN 750 tray. No issues observed. Tugged on every wire. After engine start the whine was still there, just as before.

I went through all switches on and off, adjusting the volume on both radios did not change the whine at all, even with volumes completely turned down it remained unchanged.

THEN I checked the volume on the audio-panel. Changing intercom volume had no effect. I have PMA9000EX audio-panel, an older audio-panel no longer produced. On the right side is a volume knob for music, and when I turned that down (which should have been turned to zero but somehow was not anymore), the whine went away, as in completely away, just like it has always been. I have not used that volume knob ever since I cancelled my XM music subscription about 2 years ago! At least now I can fly in alternator silence. But now I also wonder how the alternator noise gets into that output??

About 2 years ago I swopped the MFD (GDU 465) with the PFD (GDU 460) to get XM-weather in front of me. (I had issues with reliable BT connection for ADSB to GDU 460 PFD). The GDU 465 screen has Satellite receiver built in, and the music was hard wired to the audio-panel while that screen was on the right. I obviously lost that audio connection when I swopped the screens, but did not change any wiring. There was no alternator noise while I was using the XM music back then. Now, I wonder, what can cause the alternator noise getting into the audio output of the audio-panel??

Seems like it never stops!!

Thank you.

Johan

If you hook up an oscilloscope on the aircraft electrical buss *and* have the engine turning and the alternator ON, you will observe "shark teeth" of a few 100 millivolts riding on top of the 14.3VDC. The frequency ( 1/time between the peaks) of this energy is ~2000 - 3000 hz or so, which couples into audio circuits which in turn drives the coils in your headset to make a "whine"...

To fix.
* Neutralize the music input to the PMA9000EX from the GDU 460 by removing the shield, hi & lo wires from the connector going from the PMA to the GDU -- or --
* Install a sufficiently sized electrolytic capacitor, inductor to "squelch" the AC ripple...

 

[Freebird]

I just performed my first engine runs on my RV-10. I noticed audio noise, especially as the battery was charging. This is a new Plane Power alternator supplied in the Van's firewall forwarad package. Noise volume seems to be proportional to current. This is disheartening as I put a signficant effect into protecting the audio grounds when wiring.

I put a scope on the main power bus at 1000 RPM and get about 0.930 ripple (peak to peak) at 2.4kHz. Being a new build I suspected I might have some extra resistance to the battery which acts as the main capacitor for the system. I used a power supply to put 10 amps current through the system to calculate the total resistance between the alternator and battery and only get 0.009 ohm, which I don't believe would give this ripple at 20 average amps.

I have talked to Plane Power folks who where quite helpful over the phone. I am debating sending the alternator to PP to test. Before I take it off I would like to know if this is normal levels or seems excessive.

A prevous post mentioned the alternator field wire. I can also run a test with stronger field wire.

 

[bjdecker]

I just performed my first engine runs on my RV-10. I noticed audio noise, especially as the battery was charging. This is a new Plane Power alternator supplied in the Van's firewall forwarad package. Noise volume seems to be proportional to current. This is disheartening as I put a signficant effect into protecting the audio grounds when wiring.

I put a scope on the main power bus at 1000 RPM and get about 0.930 ripple (peak to peak) at 2.4kHz. Being a new build I suspected I might have some extra resistance to the battery which acts as the main capacitor for the system. I used a power supply to put 10 amps current through the system to calculate the total resistance between the alternator and battery and only get 0.009 ohm, which I don't believe would give this ripple at 20 average amps.

I have talked to Plane Power folks who where quite helpful over the phone. I am debating sending the alternator to PP to test. Before I take it off I would like to know if this is normal levels or seems excessive.

A prevous post mentioned the alternator field wire. I can also run a test with stronger field wire.

View attachment 71056

Put a 30KuF - 50V e-Cap between the B-lead and airframe ground.

 

[ariel_arielly]

I would check the battery ground connector as the battery should absorb most of the AC ripple.
If no luck, I would install a 10,000 uF capacitor between avionics bus and GND.

Good luck

and add a 0.1uF 50V in parallel with it.

 

[Janekom]

Thank you Dorfie for closing the loop. My goodness one would never thought of that. It might be that the old audio connection is now "floating" and makes a nice antenna? This made me think of an issue on a friend's RV8 years ago. He complained about his comm squelch opening intermittently. Very irritating. After days of trying everything to no avail - he mentioned that he had to undo his music in connector for some reason and re-installed it again. Guess what - the insulation washer has not been put back in and so the audio in socket caused a ground loop and interfered with the radio. It is indeed a never ending learning curve.

 

[Carl Froehlich]

I put a scope on the main power bus at 1000 RPM and get about 0.930 ripple (peak to peak) at 2.4kHz. Being a new build I suspected I might have some extra resistance to the battery which acts as the main capacitor for the system.

Just a minor comment. Batteries do not “filter” AC ripple. Batteries will absorb DC voltage spikes (to a point) but AC ripple just floats on top of the DC voltage.

Carl

 

[Mich48041]

Depending on which expert you listen to, AC ripple up to 0.5 volts or 1 volt or 1.5 volts is normal.
Quote from Bob Nuckolls,
Not once in 55 years of herding electrons in all manner of vehicular DC power systems
have I encountered an alternator interference problem in a qualified electro-whizzy
that was ‘cured’ by adding any sort of filter to the alternator.
. . . .
But in dozens of cases where alternator whine was present, the vast majority were caused
by GROUND LOOPS . . . poor installation practices in avionics wiring.