balmar 60 series alt mystery

[milagroman]

I have a 3 yr old balmar 60 series alt with the internal regulator on my yanmar 3hm35. it has started an erratic behavior of going from not charging to charging as high as 60 Amps, sometimes settling down at 20 Amps, or 12 Amps, and as low as 4 Amps but it only stabilizes at these amps for a few minutes, then stops charging and the dash light illuminates. I can get it to start charging again by turning the key to off while the engine is running and then back to on but it will continue to charge erratically again for a few minutes before going back to non charge. I've cleaned all connections and grounds and belt tension is good. Battery SOC is 12.6 and with alternator charging will be 13.8. the erratic behavior makes troubleshooting difficult? any ideas what is the problem...alternator? regulator? wiring? at my wits end.

[Morgan Sailor]

I had the same thing happen to my Balmar 60 series alternator this summer. Took it to an alternator shop. It was bad diode(s). Easy replacement, and it was back on the boat within a couple of days.