What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Alernator Noise Query

Hi all,
I have read several old threads related to the subject of alternator noise and the usual culprits, and was wondering if anyone can offer some advice. It's freezing outside so before I do any cowling pulling in the coming weeks I am trying to gather together a plan of attack.
In recent months I have acquired a whine through the headsets. If the alternator is loaded it increases in volume. The LED strobes also make it pulse louder and this is the most annoying feature. I have been through the many obvious checks, headset sockets and wiring, alternator removed and overhauled ETC ETC.
Recently I have discovered something in flight.....due to a broken heater box cable I was pushing and pulling on the handle in the panel and it affected the noise!! If I push on it, or push on the lower instrument panel near it, I can make the noise go away!!
The instrument panel is in four vertical sections with the bus bars connected across them. This is the reason why there is a bit of flex at the bottom edge near a join where the cable is fitted..not a lot though.
I'm baffled. Not being a builder I am trying to guess what is going on here..could it be the pushing on or near the heater cable is by default flexing the firewall slightly and highlighting a bad alternator/engine/earth connection on the firewall? What connections should there be? Or has anyone else experienced something similar or have any alternative suggestions before I get under the panel or pull cowlings (when it's a bit warmer)?
Many thanks in advance.
Derek Cowan

RV7A
G-RVEM
 
Last edited:
Whining

Since you are able to change the feedback by manipulating the airframe I would offer that there might be some kind of electrical ground loop.

These things are very annoying and one person's fix may not work for another.

Are your negatives on your electrical consumers generally locally grounded, or lead to a single point 'fir tree' / 'forest of tabs' grounding bus? One opinion is that if we locally ground (use the airframe for our negative) we set ourselves up for very small potential differences in conductivity owing to how the airframe is assembled.
 
Last edited:
Seems as though the cable is carrying some of the grounding load. I would make sure the grounding of the engine to the airframe and battery negative post is clean and tight at the connections. Also look at where the avionics are grounded to make sure there is nothing there that is lose, could even be a bad fast on spade connector at the "forest of tabs" if ground was accomplished that way.

If that does not clear up the problem take a close look at the crimped ends of the grounding cables.
 
Last edited:
Thanks for the suggestions.
If it adds to the story, the 1/4 section of the panel in question has the transponder, VHF and intercom boxes fitted. One item that gave some grief a long while back was the Flightcom 403 intercom. It started crackling through the headsets so I discovered by wiggling it on the panel that that cured it, so although the earth connection seems good I attached a further earth wire from it's body direct to earth which cured the issue..but it now has two earthing points. So, I don't know if this is still an issue. Removing the secondary earth wire I attached makes it crackle so bad to be unusable.
To answer the points above, (again I didn't build) all the earth connections go to one of two studs on the sub panel behind the main instrument panel.
Thanks for suggestions however on checking the major earth connections and all other connections.
 
Noise sorted

Just for the benefit of anyone reading this and wondering what the cure was..it was not what I expected!!
Pulling on the panel made the noise come and go, so tugging on each item I narrowed it down to the Garmin GMC507 head. It appears that the 507 earths on the panel via the two locking tabs. So, 507 off, cleaned paint off the rear of the panel at the tabs..back together, sound gone!!
Don't know how that all works but the strobe noise/whine noise has gone.
Thanks for all earlier advice.
 
Back
Top