Finn Lassen wrote:

As discussed extensively on Matronics.com's Aero-Electric list, a

run-away  alternator can easily put out more than 100 volts! By run-away
I mean a failed voltage regulator feeding full 12 volts into the field
winding (B+ lead).

I don't think that the field lead amperage (from the voltage

regulator) is very high, so efficiency in the voltage regulator is not a
major factor.

Having said all that, I've still not modified my Mitsubishi (?)

alternator to include the crow-bar over-voltage protector. But if I had a
$10,000 avionics stack in my plane, you can be sure I would.

Finn

Somehow I doubt that 100 volt number.
Sounds like a good way to make a buck.

Must be a very rare failure mode or car radios and EFI/IGN  computers
would be dying all over the place. With 12 volts applied to the
field how long before the wires feeding it fused?

With a battery across the output from the alternator the connection
to the battery must also somehow disappear as the battery
would look like a giant short to 100 volts.

Further more 35 volt zeners on the input to most electronic equipment
would do the job. Perhaps there could be a 100 volt spike but a
capacitor could handle that and knock it down to way less than 35 volts.

Color me skeptical.
Paul Lamar

"Perry J. Mick" wrote:

Soon after I bought my '86 RX-7 in '96, it had a voltage regulator
failure.  It was passive, basically a dead alternator.  Replaced
the regulator inside the alternator, has been working fine since.
--
Perry Mick
Duckt N7XR
http://www.ductedfan.com

Mike Wills wrote:

  Nuckolls shows a simple means of providing overvoltage protection for an
internally regulated alternator on his website. This seems like a cheap and
easy mod worth doing and is a cost effective compromise compared to buying
one of his external regulators with built in OVP.

Mike Wills

 
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