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Hi All,
Mark wrote:
> I'm not an expert in electronics. I was following the advice of Bob
> Nuckols on the Aero-electric connection. There are failure modes with
> internal regulators such as a "run-away" that can't be stopped by shutting
> off the field current. This possibility necessitates using over-voltage
> protection at a very minimum. The problem comes with how to hook OVP up to
> an internally regulated alternator. There's a schematic on the
> Aero-electric Connection at
> http://www.aeroelectric.com/articles/bleadov.pdf that shows how to do
> that.
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.
crowbar.jpg
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