Alternator Problem?

[nigel1]

Once only "fault" occurred on last trip with the engine driven alternator.
Alternator is a Valeo 12V 70Amp.

Had been sailing, wind dropped, started engine, all seems OK.
Went below to check position, and as I usually do, checked the battery monitor, which was showing 13.4V and 8 amps.

I also have solar and a wind generator, but with the engine running, the monitor should have been indicating between 14.2 and 14.4V (there is an external Adverc rectifier which ups the stock alternator rectifier to 14.4V)

First I checked the voltage across the battery terminals, which was 13.4V, then checked the voltage across the +ve and -ve connections on the back of the alternator, that was 16.6V, which was way to high.

I then stopped the engine, waited 5 minutes, and then restarted. Alternator voltage back to normal, and the battery monitor indicating that the Adverc rectifier was operating correctly, which is cycling between 14.2V for 5 minutes, then 14.4V for 15 minutes.

There is a Sterling Pro Split R in the system, which has input from the alternator and then splits the charge to the house and engine battery banks. If this unit senses an input voltage from the alternator of more than 16V it will isolate all battery banks from the alternator, so this explains why the monitor was showing 13.4V and the actual terminal voltage was 13.4V, as no charge from the alternator was being passed to the batteries.


Question is, anyone know the likely cause of why the alternator went to 16.6V on this one occasion. Since this incident, the engine has been run for about 4 hours, and the alternator has worked as it should.