Alternator antics

[Canuck]

My alternator acted up on my flight back from Fredericton to Ottawa this morning. I will be talking to the shop on Monday and limiting myself to day VFR circuits until they sign off that it's serviceable (no well-intentioned advice needed on that point), but I'd still be grateful for musings from the list.

Symptoms (the alternator warning light didn't go on during the following, except when I tested it)

- about 30 minutes out, the ammeter needle started oscillating wildly, with an audible cyclical whine, for about a minute, the settled again (strobes were not on)
- it did it again 10 minutes later, and lasted longer; turning all unnecessary electronics off and unplugging all USB devices didn't help
- about 10 minutes later, it started oscillating continuously
- voltage display on my Stormscope (which I left on for the rest of the flight) was steady 13.1v when not oscillating, but going from 12.8v to 13.4v during oscillation
- turning the alternator off and back on didn't help
- turning the alternator off for a minute, then back on, showed oscillations at first, but then settled down to a steady 5amp for the next 2 hours
- turning on my strobes near destination started the oscillations again (not the normal strobe oscillations, but wild ones right back to zero), but it settled again about 15 seconds after I turned the strobes off
-the voltage display stayed steady at 13.1v until the end of the flight (I was in solid IMC, so I was watching it like a hawk)

Thanks in advance for any diagnosis, amateur or professional.

 

[EchoDelta]

 

[Ray93J]

 

[Canuck]

 

[EchoDelta]

 

[flyguydon]

 

[sanjiv]

 

[JimICS2452]

 

[Canuck]

 

[Ray93J]