nuckolls.bob(at)aeroelect
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 Posted: Wed Jun 03, 2015 8:10 pm Post subject: Alternator Noise plus Volts & Amps Fluctuating |
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At 09:31 PM 6/3/2015, you wrote:
| Quote: | I had the opportunity to do a 7+ hour X/C a week or two ago and it was driven into my head that I have a soft ~3 CPS noise in my headsets and the voltmeter and ammeter readings are fluctuating at the same time and frequency as the noise. If I turn off the alternator, the noise goes silent and the ammeter and voltmeter stabilize too.
The ammeter shunt is measuring battery charge or discharge and the voltmeter comes off of the buss downstream of the diode. Both gauges are analog, and the needles are bouncing up and down by a half volt (13.5-14V) and a half amp or thereabouts. The alternator is the B&C 40 amp unit and the regulator is the Ford unit recommended 15 years ago when the airplane was built. All of the components have been in service for 14 years and have approximately 950 hours of use on them.
Any suggestions on rectifying this condition?
Thanks,
Kyle Boatright
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The voltage regulator sense voltage shares
a path with alternator field current in this
regulator. This condition is well known in
architectures of this type and is offten called
the 'galloping ammeter'. In the older Cessnas,
I recommend replacing everything from the bus
bar to the regulator which would include breaker,
alternator switch and wires.
Doing any ONE thing might 'cure' the problem but
it's the sum-total of environmentally driven resistance
creep that finally stacks up to cause the instability.
You may cure it with one replacement but only by
replacing ALL will you get back to as-new condition.
See http://www.aeroelectric.com/articles/Alternators/Know_Your_Charging_System.pdf
Bob . . . [quote][b]
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