I have heard all of this before and am still electrically confused. I have a few theories but no proof. In the face of my theories is the fact that it is not consistently repeatable. So here goes.
Turn the battery off while running and the alternator suddenly goes to full output kinda like shifting to 1st while going 70mph. I get that. The sudden high current overheats the diodes and they fail open. Turn the key off while running and one of two things happens. 1st option is that nothing about the alternator is wired to the ignition and nothing happens. I believe that this is the situation with the ignition system in the video I posted earlier in this thread. As mentioned by others the battery and voltage sensing lines are basically directly connected to the battery so turning the key on or off doesn't affect anything. I also think this is the slow and very low battery drain which someone else mentioned. The 2nd option is that the ignition is attached to the sensing circuit as in the schematic. The switch turns on and off the regulator and subsequently the rotor field. This would apply to alternators with either the internal or external regulator. As the regulator is turned off this might be causing a momentary high counter electromotive force or an unopposed stator current (surge). Or maybe a sudden full reverse bias current of the diodes. This is obviously the confusing part. I've never figured it out and until someone else explains it I don't plan to make a habit of turning off the switch or the battery. Josh Muckley S/V Sea Hawk 1989 C&C 37+ Solomons, MD Couple other data points: - The diesel mechanic gave me a huge DUH ! when I explained what had happened.. He said, you just learned the hard way that you should never turn off the ignition key on a diesel while it's running. What happened was punishment for my brain fart.. The guy fixes diesels for a living - The alternator shop I talked to said the exact same thing. Burned diodes blah blah, happens all the time to new diesel owners.. - Francois Rivard 1990 34+ "Take Five" lake Lanier, GA _______________________________________________ This list is supported by the generous donations of our members. If you like what we do, please help us pay for our costs by donating. All Contributions are greatly appreciated!
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