Al, you are right about now having the lack of
over-voltage protection. All I have in line is a fusable link rignt
now. Fortunately, all of my expensive avionics can tolerate voltages of
at least 28V without being affected.
If a voltage regulator fails, how high can the voltage
go?
Until something fails. The assumed
failure is full-on field current, so the alternator puts out max rated current
until . . . . The stock built in regulators adjust the output by
doing a fairy high frequency, square-wave, on-off switching of the field
current; with the on time adjusted to maintain ~14.5 volts. The most
common failure mode is no “on” time, and the battery voltage drops.
I don’t know by direct experience, but Bob Nuchols says they can
fail full “on”.
Al
Dave;
That’s
interesting. Makes me wonder whether I should put a scope on voltage and
see if it is smooth.
The downside of
connecting the field to the output, as I’m sure you know, is that you now
have the risk of a runaway voltage condition if the VR fails. I guess the
odds are low, but the costs could be high. Avionics?
I assume that you have a
breaker (or fuse) in the alt field circuit. You can put a
“crowbar” circuit between the field lead and ground that will trip
the breaker in an over-voltage condition. I got one from Aeroelectric.
Al