Anyboy have an idea what it means when the Alternator voltages are "dancing" like this? Could this have to do with my Autopilot "disconnecting"?
http://cirrusreports.com/flights/G-YORC/701765
(This is the Cirrusreports site where you can uplod all data from the MFD. A complete logbook and all engine parameters)
It looks like a voltage regulator problem (well of course it does...). Everthing is fine until the battery is fully charged as you can see on the "current" page. Once that load is away, it starts oscillating. I have no idea how the regulator is built, but if it has some kind of dummy load I would start looking there.
Yes, a duff voltage regulator.
The voltage varies from 28.2 to 29.2 and that is way too high. 28.0 is about right for the battery.
I bet you that if the battery connection came off, it would blow all your avionics up.
The battery is very likely being trashed by a massive overcharge. OTOH maybe not because the Amps graph on Alt1 is showing only about 10A.
Yes it might not help the autopilot either...
Thanks, you two I put it in the COPA website aswell, let's see what the Cirrus specialists say. There is a note in the POH that there will be a warning on the PFD when the voltage is above 32 Volts ... so maybe it still wasn't critical. But I really know (almost) nothing about electrical systems
32V should not blow anything up in itself, but if you have a "24V" lead-acid battery connected across such a voltage source, there will be a massive current flowing into the battery, regardless of its charge state.
If I saw anything like 30V during a flight, I would switch off the alternator field to protect the battery. But maybe that could lead to an alternator failure; I don't know what sort of voltage an alternator could generate with the maximum current through the field winding and going round at 2500rpm... 100-200V maybe?
Thanks, interesting that they didn't find a bad voltage regulator at the 50 h inspection ...
Th 50hr check is done with the engine off 
They should warm up the oil thoroughly if they are taking an oil sample for analysis - are they?
Also the voltage problem may not be obvious at engine idle. For example my standard engine ground idle is 1200rpm, and one needs 1100rpm just to bring the bus to the point where there is no net drain on the battery.
I don't know where the battery is in a Cirrus, but if there's any way to put a DC clampmeter on one of the cables within sight of pilot or pax then any sustained charge of more than say 20A would mean imminent battery death. Anyway, you'll gag on the sulphuric acid fumes!
Of course one part of a 50 h inspection is an engine run to warm up the oil, one more after the oil change - and a last one with high power to check all the engine data, and the electrical system ... and still they didn't see it
From the maintenance manual:
.... The pilot has access to the alternator circuit breakers, which are located in the circuit breaker panel,during flight. If the system is generating more than 31.75 ± 0.25 V, the corresponding alternator circuitbreaker will open, preventing further power generation by that alternator.
