Re: Diode in alternator system

Posted by jdemaris on March 05, 2005 at 20:11:00 from (209.23.30.184):

In Reply to: Re: Diode in alternator system posted by George S. in the real NY on March 05, 2005 at 17:44:51:

I've heard such complaints but haven't seen it on a good alternator. Most alternators have an isolation diode built into them (or a set of them) at the output. Delco 10SI and 12SI also have a diode-trio that sometimes fails. On any and all the machines I've worked on that had a complaint about slow battery draw down, if the alternator was causing it, it had a bad diode. I've also seen a few that were wired wrong, and the drain was caused by the field left energized all the time. That's not an alternator problem. Also worked on a few cars and trucks with similar complaints, put a milliampmeter on them, and found the draw being caused by things like electic clocks or radio memory chips that are energized all the time. I'm in the habit of checking any alternator that I install, it's easy, just hook a milliamp meter to it and check for draw. A simple amp meter does not read low enough. If a diode is bad at the isolation-output end of the alternator, it will draw batteries down. If if has bad diodes at the rectifing bridges, then is will have low ouptut.
I've got several tractors, backhoes, and crawlers that sit all winter without being run, and they all have Delco alternators on them - and I have no problems with current draw when sitting.

Follow Ups:

• Re: Diode in alternator system Joe (Wa) 20:56:15 03/05/05 (0)

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