Troubleshooting alternator noise

[AaronG]

I'm looking for some advanced ideas on troubleshooting alternator noise. I searched the achieves and have not found anything that works. Here are my details:

RV10 with IFR panel
Plane power 60A main alternator
High pitch noise that stays at constant pitch but gets louder with load
Existed since day one with new PP alternator
Noise is eliminated when main alternator is turned off
Noise is eliminated when ps8000b intercom is turned off
Noise is eliminated with b&c backup alternator and zeftronics regulator
Both alternators go to same main bus copper bar
All jacks have isolation washers
Adding the lonestar alternator filter at the PP alternator did nothing

Any ideas for next steps. Right now i'm thinking of returning the PP alternator, or adding an inline filter to the intercom. Any ideas for a light and inexpensive filter? The ones for sale look both heavy and run $100 plus. Given that the alternator filter did nothing, I'm hesitant to spend more on filters.

[Walt]

If the alternator is "good" the noise is caused by high a resistance in the circuit somewhere, either the power or ground circuit to the alternator. I would start by checking all the cables and terminals starting at the alternator and going all the way back to the battery, also verify the alternator is properly grounded to the engine case. A bad crimp or bad connection somewhere is likely the problem. It could be a bad regulator in the alternator but I would check all the connections before condeming it.

Adding more filters is not the answer so don't waste your $$

[rocketbob]

Alternator noise is almost certainly caused by a bad diode in the alternator which causes a ripple AC voltage to appear on the bus. Easy way to check for this is to put a voltmeter on your bus turned on to AC and note if there is an AC voltage present when the alternator is on. If there is, replace it. A better instrument to use would be an oscilloscope if you have access to one.

[jthocker]

Originally Posted by rocketbob

Alternator noise is almost certainly caused by a bad diode in the alternator which causes a ripple AC voltage to appear on the bus. Easy way to check for this is to put a voltmeter on your bus turned on to AC and note if there is an AC voltage present when the alternator is on. If there is, replace it. A better instrument to use would be an oscilloscope if you have access to one.

Ooh an oscilloscope, I think I have room for one of those in my panel!

[Ironflight]

Do you happen to have a 296,396,or 496 in there with ship's power and audio coming out of the jack and into the panel? The hardware in those units isn't isolated properly, and it is a common source of alternator whine getting into the audio system. They seemed t have done better on the 696. Just another thing to check.

[Walt]

Originally Posted by rocketbob

Alternator noise is almost certainly caused by a bad diode in the alternator which causes a ripple AC voltage to appear on the bus. Easy way to check for this is to put a voltmeter on your bus turned on to AC and note if there is an AC voltage present when the alternator is on. If there is, replace it. A better instrument to use would be an oscilloscope if you have access to one.

Bob, you are correct, however, a bad regulator will cause increased alternator noise intensity (get louder) with increased load but is not affected by RPM. A bad diode will cause a change in pitch with RPM changes and is generally not affected by load.

Hence my deduction that this alternator may suffer from a bad regulator, but I would still check all the connections and grounds first.

[rocketbob]

Originally Posted by jthocker

Ooh an oscilloscope, I think I have room for one of those in my panel!

You do not!

[Walt]

Nano O scope for your panel, I think I am going to add one of these to my own panel now, good conversation piece!