Transient alternator problem

"Jeremy Lew" wrote in message
...
Was flying IFR in the clear on top of an overcast layer today. I noticed
at
some point that the ammeter was indicating zero, and not moving. The Alt
warning light was not illuminated, except when I pressed the test button.
I
started to shut down non-essential electriconics in case this was for
real.
After a minute or two, the ammeter needle resumed normal indications, and
stayed that way for the rest of the flight. The Alt warning light was
properly illumated during low-RPM operations on the ground, as well as
during the engine runup split switch check.

The warning light/ammeter needle discrepancy suggests to me that problem
was
in the ammeter, and that the alternator was functioning normally the whole
time. Anyone have any theories as to what would cause indications like
this? Is external RF interference possible?

(x-posted to rec.aviation.owning)

What a coincidence, we've had the same sort of intermittent problem with our
charging system on the last few flights! Of course, when we've had our
voltmeter there to diagnose it, it seems to work perfectly

Will let you know what we find-- please do likewise!

(Ours is a 1978 Cessna 210M - IO520).

Cheers,
John Clonts
Temple, Texas
N7NZ