Alternator Whine

[jbondy]

We recently reinstalled higher output Balmar alternator (90A) and external regulator (Balmar ARS III) replacing the original Yanmar unit on our 3YM30. There is a delay in the charging cicrcuit when the engine is first started to allow it to warm up before the additional load of charging is placed on the engine. You can hear the engine slow when the charging starts. Whe the belt isn't adjusted properly, you can also hear the belt squeal at that point. We had these units installed on the engine we replaced and were familiar with these symptoms. Something new is happening now, though. When the charging starts we get a whine that seems to come from everything electronic, the VHF radio, the stereo, etc. We even hear it when these things are off. Any ideas what this is and how to filter it out of the system?

Thanks in advance.

[Rockter]

If the batteries are discharged a bit, the whine is normal. My old Ample Power alternator whines at high load. Keep the engine revs up at that moment or the belt tension will soar and the alty is likely to overheat. It really does need the fan spinning fast on the front of that alty.

Maybe you are charging at too low a rev there Jb?
When you first start charging, keep those revs up. If you are planning on leaving the dock, get some reasonable charge in there first. On no account take off at idle, or near idle with the alty working hard. It really does not like it, nor does the belt. You can see the belt chattering under the load then, and it tends to shed bits into your ears and eyes.

Keep revs up. Absolutely no idling, or low revs, at that moment.

[jbondy]

The batteries definitely were discharged at that point. I reacted exactly the wrong way. I reduced engine speed to reduce the whine when I should do the opposite. I also thought those little vanes on the hub of the alternator were only structural. I didn't think they contributed cooling. Very informative. Thanks.

[cpubob]

If you hear the whine in devices turned off I would suspect a bad diode in the Alternator. The alternator produces ac, that gets rectified to dc with the diodes, these guys have to handle huge amounts of current, if one blows it will most likely open, so now the other diodes are working harder and not giving you pure DC producing an audible noise. Use a multimeter in the AC scale, looking at a battery that is being charged, you should see very minimal amounts of ac component riding on the plus 14-15 volts out of the alternator, my guess would be less than half a volt. There is also a capacitor on the alternator to help filter noise, this cap could be bad or not connected. If the regulator and alternator are new, the chances are they are not the problem, maybe a loose ground wire on the alternator or at the bus bar.

Lets hope for a loose wire.

Bob
Pearson 28-2 "Lila"