Warm alternator

[exMaggieDrum]

My engine alternator (Balmar 125A) stays warm to the touch with the battery connected and the engine not running. I have seen this on other boats and I believe it happens on cars/trucks as well. My boat does not have an ignition switch so the only way to completely disconnect it is to turn the starter battery switch to off.

It is regulated by a Lifeline automatic regulator and the output goes to the house batteries.

Can anyone explain what is happening to make it stay warm? Obviously it is from resistance heating and is using battery current and is not something that I want to just leave on. I may install an ignition switch so I can leave the starter battery connected at times when sailing so I can start the engine quickly if needed.

[Cheechako]

I don't think any of mine have stayed warm. Not sure what your problem is though. Bad diode?

[Lepke]

Alternators have diodes that sometimes fail. Diodes in a circuit only allow electrical current to flow in one direction. Most alternators are not disconnected from the batteries when not running. They have 2 banks of several diodes. If one fails, the alternator may still function, but will allow current to drain thru the alternator to ground. Without your charger, the batteries would go dead. It is probably drawing more shore power than normal.
Diodes are easy to change. There are sites on the web that sell parts for most common alternators. I would fix or replace the alternator soon. Many auto parts stores will test alternators free. Until you fix, you should turn off your battery switch or disconnect the alternator. The current draining is going to ground and might be eating your zincs.

[smac999]

is your regulator always powered on? sending field to the alt?


your regulator should only be on when the engine is on. if you don't have a key / ign. then it should be controled with an oil pressure switch.

[exMaggieDrum]

Originally Posted by smac999

is your regulator always powered on? sending field to the alt?


your regulator should only be on when the engine is on. if you don't have a key / ign. then it should be controled with an oil pressure switch.

Excellent idea on the pressure switch. Except the alternator is regulated via a Lifeline regulator. I do not have any experience with this model so need to see how it is supposed to work. The Balmar regulators I have used in the past are turned on via an ignition switch or the oil pressure switch so the field is not turned on until then. The Lifeline may not do that so I need to dive in to it and check it out. The question still remains whether the alternator should warm up with the field on and no rotation of the alternator.

Note: I just looked up the Lifeline Next Step docs and it shows the regulator is supposed to be hooked up the same. The previous owner made some prior mistakes in wiring things and I need to see how it was done. That may solve the immediate issue. Thanks.