Without regulation, the output voltage will track the RPM of the alternator. Thus, if it can put out 14.7 volts at idle, (800 engine RPM) it will put out about 120 volts at 6500 engine RPM. As fuses pop and the load is removed, this voltage would likely go even higher.

At 05:17 PM 10/6/2004 -0700, you wrote:

 

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 ontime, and the battery voltage drops.  I dont know by direct experience, but Bob Nuchols says they can fail full on.

 

Al

 

 

 

Dave Leonard

Dave;

 

Thats 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 Im 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 crowbarcircuit between the field lead and ground that will trip the breaker in an over-voltage condition.  I got one from Aeroelectric.

 

Al