erratic functionning of alternator

Hello,
The internally regulated 50 amp PlanePower alternator fitted on my O-320 has a bit of an erratic functionning:
1- the field line remains "ON" most of the time whatever the position of the Alt switch, as evidenced by the amp meter showing a 3 amps draw before startup. (the switch itself is functionning properly)
2- when running, the alternator generates every now and then some overvoltage (15V+) which is easily corrected by resetting the alternator (off-on using the 50 amp breaker rather than the field switch which is inoperative).
Has someone any hints for a fix or should I just send it for maintenance.
Thank you very much.
Olivier
RV4

To the OP - without additional detail it's difficult to surmise the problem; but here goes some observations:

You state the field wire is "ON" evidenced by current flow; this isn't necessarily the right indicator, much depends upon where/how the current draw measured, specifically where is the current shunt or loop sense connected in your system?

By chance did measure the field wire voltage at the connection to the alternator? If so, what was it?

You describe a method of resetting the alternator which has potentially catastrophic effects on the rectifier circuitry of the alternator as well as other devices. (see https://en.wikipedia.org/wiki/Load_dump).

Thank you Brian. You're right: my belief in "Field ON" whatever the position of the Alt switch not only comes from seeing of a 3amp draw but also from the fact that this draw comes to almost nil when the alternator breaker is pulled...but perhaps I draw a wrong conclusion.
Potentially scary effects indeed when pulling the alt breaker...I've been lucky then that there hasn't been any of these yet !

Salut Olivier. I had the same problem on a 3 hrs flight recently. Turns out that the ground wire at the battery wasn't tight enough and easily corrected by adding a star washer and torqued to spec. I would start by checking all electrical connections between the alternator and the battery as it most likely where you will find your problem. Bon courage
Michel

Merci Michel! Sounds like a sensible way to proceed.