voltage regulators...
 

Hi guys, I forwarded this to CPA... any suggestions?

Hi Tom,

Guy Paris here. I have chatted with you before on my 1977 337 G on different issues. Recently I noticed on my E I volt amp gauge a difference in voltage from front alternator to the rear. The front alternator reading about 29.3 volts with radio master and landing lights on. We then lowered the voltage to within about .3 volts of the rear which was at 28.5 volts. Off I went flying. Looking at the gauge the volts on the front alternator when isolated, it would go up and down in volts. Up to 30.0 volts down to 28.0 volts. (+/- .02 to .04 volts). What do you think, is it the regulator? If so should they be changed in pairs? Thanks, Guy Paris....

Guy:

I think what you have is some resistance in one of the components of the field circuit...master switch, field switch, circuit breaker, or connection. Even a little bit of resistance will cause the voltage regulator to hunt. This is what causes the panel lights to flicker at night.

I had the problem and cleaned all the connections I could find. The problem was still there. I replaced the master switch and alternator switches, and the problem disappeared. The amount of resistance measured between the old switches and the new switches was negligible, but it was enough to cause the problems.

Mark

voltage regulator (s)
 

Thanks Mark. guy

I have had the switch problem in my '67 model too. I replaced the master and alternator switches. I broke open the switches and you'd be surprised how dirty the 35 year old contacts were. That carbon buildup seems to make the alternators hunt for stability. After replacing the switches the problem went away.

There are four switches in series with the field input to the regulators. Take a look at the technical data page of this web site for a simplified electrical charging diagram. It may not be exactly like your aircraft but may help a little with troubleshooting.