On 2 Aug 2005 07:59:29 -0700, "argon39" wrote:

Recently I have noted an in-flight system voltage fluctuation in my
C-172K. The fluctuations are quasi-periodic, with an amplitude of about
0.4 volts and a period that varies between about 1.6 and 1.8 minutes.
The varations are contained within a band between 14.0/13.9 and
13.6/13.5 volts (the monitoring system quantizes to +/- 0.1 volts).

I have posted a graph of these observations for two 1.5 hour flights at
http://home.comcast.net/~argon39/Vol...luctuation.pdf

On my PA28-180, I had a somewhat similar problem which I diagnosed to
be a bad circuit breaker causing varying voltage (IR) drops in the
voltage regulation circuit. The circuit breaker was exhibiting slight
and varying resistances when force was exerted on the case of the
breaker. Aiframe vibration and turbulence was apparently enough to
change the force on the breaker, which randomly varied the resistance.