I've got a Volvo Penta TAMD installed in my boat. The alternator charging light and alarm comes on intermittently when over planing speed.

Had a new alternator and belt fitted last year. Alternator is testing fine with a voltmeter and alternator/battery tester. Batteries all test okay.

The alarm is coming coming on when the batteries are fully charged. It'll come on for a second or two, up to 30 seconds, before going off. It'll stay off for a few seconds up to a few minutes. So no pattern to it. It seems to not happen below planing speed.

Had the belt adjusted by a mechanic recently and it seemed to be okay for about 30 minutes of running, then the alarm started going off again.

Also have solar panels running through a controller that is on all the time, and a voltage sensitive relay to make sure the start battery gets fully charged first.

Anyone have any ideas on possible causes for the alarm? The mechanic is a bit stumped by it.