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Dale R,
Sorry for the long delay, but I sometimes need time to digest new ideas. Your OV circuit looks very interesting, and indeed simpler as well as lighter than the A/E design. I was wondering if you could explain how the SCR causes the circuit breaker to trip. I take it that it just siphons off a heavy enough load to finally trip the breaker? If so, how long would that take (I don't want to smoke other components while the SCR is still asleep).
Thanks,
Mark S.
I acknowledge that Bob Nuckols is far more knowlegeable about things electronic that I am, but that schematic sure seems like the hard way to implement what is basically a "crowbar" circuit. I've attached a quick-and-dirty MSpaint drawing of a suitable circuit to isolate the alternator from the battery and load (assume that the load is taken from the positive pole of the battery on this drawing - I forgot to put it on (told you it was quick-&-dirty)).
The SCR needs to be rated for more amps than the maximum normal output of the alternator. The Zener only needs to pass enough current to trip the SCR; I chose 15V assuming that normal max-charge is 14.5V pick a higher voltage, if your system requires. The resistor is to limit current flow through the zener to less than its rating - five ohm would probably work fine, it won't be conducting very long anyway.
The circuit breaker could be an automatic resetting (after a cool-off period) but I don't recommend it. If the alternator went ballistic in the air, I'd want it to *stay* off until I had a chance to check it out on the ground.
Regards,
Dale R.
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