On Wed, 19 Apr 2006 12:06:37 -0400, Jonathan Goodish
wrote:

In article ,
David Lesher wrote:
I put a voltmeter on the alternator output and measured between 32-35 AC
volts at moderate load and moderate RPM. Looks like some diodes have
decided to give up.

Maybe. Voltmeters are a really bad way to look at how much non-sine AC
ripple there is on a DC bus. Unless it's a known-good "True RMS" meter
with AC-only coupling, it will lie.

I've lost track; do you have audible whine in the audio? Does it
change with load?

David,

I suspect that the meter isn't going to be 32 volts AC off the mark,
even though it isn't a True RMS meter. The recommended threshold for AC
voltage from the alternator is anywhere from 0.8 to 1.0 volts, based on
the documentation I've read and my discussions with an engineer at
ElectroSystems.

However, I have alternator whine in the audio which changes with RPM and
load. I've tried just about everything else to get rid of the whine, so
this is about the last thing I know to do.

Does your plane have a split master switch? If so, shut down the
alternator while flying and see if whine goes away.

-Nathan