231 alternator coupler slipping?

[231LV]

I fly a 1980 231 with the 12volt system. After 7 years, I replaced the battery (the BatteryMinder paid for itself). Shortly after, I noticed the ammeter gently "bouncing" at low rpm. The charge was a typical 14.1 volts right after startup to 13.7 volts in cruise. I never noticed the ammeter even moving during the previous years with the old battery ( which is the same as the old one). I didn't notice any other abnormalities so largely ignored the gently bouncing gauge....until a recent trip. Over the course of the 4 hour flight, the ammeter went from a gentle bounce after startup to a swinging needle from plus to negative. The Hi/lo voltage light never came on. I'm wondering whether this could be the result of a slipping alternator coupler or the alternator itself? I suppose it could also be a poor ground or voltage regulator problem, as well. I replaced the coupler several years ago but don't recall the symptoms which led me to replace it. I plan to take it into the shop but wanted to see if there might be any thoughts which could narrow down the cause before I spend the money on shop time tracking down the problem.

[Guest]

With the engine cowl removed, insert your finger into the fan opening of the alternator from the left side. Slowly turn the prop by hand. If you are able to hold the fan with your finger, the drive is slipping.

Clarence

[larryb]

The alternator field current goes through half of the master switch. A bad connection here, or a problem in switch itself can lead to a swinging needle. Basically any high resistance connection anywhere in the field circuit will cause this, but at the master switch is pretty common.

[BillC]

Check out this publication. Click on fifth article down, "fluctuating ammeters".

http://www.donmaxwell.com/publications/publications.htm

[231LV]

Thank you all!!! Excellent suggestions