Thanks Perry. I've had several people tell me the C21 will run just fine on external 12V. I also found this info on the Ten-Tec DC Circuit Breaker Model 1170: http://www.tentecwiki.org/doku.php?id=1170 I'm now on the lookout for one of these Airpax T-11 5 amp fast acting breakers. 73, -Josh WA7FPV