This weekend, during a long cruise, a friend of mine radioed that he was having concerns about his engine (Universal M35B) and something didn't smell right. When I arrived he was running his engine and there was a clear burning smell. We removed the engine cover and found sparks flying from the alternator output. He shut down the engine, turned off the "perko" and another friend joined us in the diagnosis.
The battery bank is about 400 AH and I believe the alt was more than 80A with an external Balmar regulator (equipped for alt temp sensing but not installed). What happened was that the alternator output nut had worked loose (diesels are known to vibrate) and the joint had become resistive. That joint, driven by alternator and in part by the external alt regulator, got so hot that it melted nearby wires and the alternator output stud isolating standoff. The stud in turn, able to move, was intermittently shorting to the case. A post mortem revealed that the stud was white with oxidation suggesting it was red hot at some point. Furthermore, since the battery cable system was not fused at the battery (per Mainesail and ABYC recommendations), the short took out the "Perko" switch and melted adjacent wires. It was fortunate that our other friend has an awesome spares kit (and some fantastic wiring and diagnostic skills to boot) and actually had a switch that fit the panel. This was all caused by a wire in a high capacity alternator system that had worked loose. We disconnected the alternator, he got his batteries charged with a generator and he made it safely home without incident.
The cautionary message: check your connections regularly on a high current system and fuse your batteries. Our friend was very fortunate to not have a fire on-board. Hope this information helps the next person.
The battery bank is about 400 AH and I believe the alt was more than 80A with an external Balmar regulator (equipped for alt temp sensing but not installed). What happened was that the alternator output nut had worked loose (diesels are known to vibrate) and the joint had become resistive. That joint, driven by alternator and in part by the external alt regulator, got so hot that it melted nearby wires and the alternator output stud isolating standoff. The stud in turn, able to move, was intermittently shorting to the case. A post mortem revealed that the stud was white with oxidation suggesting it was red hot at some point. Furthermore, since the battery cable system was not fused at the battery (per Mainesail and ABYC recommendations), the short took out the "Perko" switch and melted adjacent wires. It was fortunate that our other friend has an awesome spares kit (and some fantastic wiring and diagnostic skills to boot) and actually had a switch that fit the panel. This was all caused by a wire in a high capacity alternator system that had worked loose. We disconnected the alternator, he got his batteries charged with a generator and he made it safely home without incident.
The cautionary message: check your connections regularly on a high current system and fuse your batteries. Our friend was very fortunate to not have a fire on-board. Hope this information helps the next person.