Roger Long
Senior Member
We have an old and simple trawler with twin engines and minimal 12 volt loads. There is no house bank, just an 8D for each engine and the master switch can draw house loads from either or both. We have a generator so I have always left the switch on “Both” on the theory that I’m cutting battery draw down for cabin and anchor lights in half for better battery life. If I should draw them down too far for the engines to start, I can just run the generator for a while. Stove and refrigerator are 120 volt so I start the generator first thing every morning and starting is never and issue.
Recently, I’ve had some mysterious problems with the tachs on one side. Both fly bridge and lower helm behave identically. For a couple days, I would have to run the engine up to nearly full rpm in neutral to get them to come alive. Then, they died with the needles just barely flickering near zero. Alternators were just bench tested and check out. The tachs for the other side are fine.
It’s been suggested elsewhere that a slight drift in the voltage regulator set point or tiny resistance difference in the wiring is causing the voltage from one tach to fool the other into thinking it doesn’t need to start producing power. I’m away from the boat for a month so I can’t experiment but I’d appreciate some thoughts. If I put the master switch on 1 or 2 to isolate the systems and the tach comes alive, the theory will have been proven. If that doesn’t work, I’ve got to plan a day of wiring trouble shooting.
Any other issues with running two alternators to two connected batteries that I’m overlooking? No other problems in the last 4 years. I do know that a bad cell on one battery can take out the other but I keep a close eye on them to be sure the voltage of each remains the same.
Recently, I’ve had some mysterious problems with the tachs on one side. Both fly bridge and lower helm behave identically. For a couple days, I would have to run the engine up to nearly full rpm in neutral to get them to come alive. Then, they died with the needles just barely flickering near zero. Alternators were just bench tested and check out. The tachs for the other side are fine.
It’s been suggested elsewhere that a slight drift in the voltage regulator set point or tiny resistance difference in the wiring is causing the voltage from one tach to fool the other into thinking it doesn’t need to start producing power. I’m away from the boat for a month so I can’t experiment but I’d appreciate some thoughts. If I put the master switch on 1 or 2 to isolate the systems and the tach comes alive, the theory will have been proven. If that doesn’t work, I’ve got to plan a day of wiring trouble shooting.
Any other issues with running two alternators to two connected batteries that I’m overlooking? No other problems in the last 4 years. I do know that a bad cell on one battery can take out the other but I keep a close eye on them to be sure the voltage of each remains the same.