On Sat, 1 May 2010, Eric Lemmon wrote: > A fan blowing on a transmitter heat sink does absolutely nothing > immediately after the transmitter is keyed, since the heat sink is > likely at ambient temperature. It takes a period of time for the heat > sink to warm up, so operating the fan prematurely is a waste of > energy- which may be an issue for a solar-powered repeater. > > IMHO, the most efficient means of fan control is also the cheapest: > A thermal switch. My first choice is a Cantherm #R2005015 > normally-open thermostat that closes at 50 degrees Celsius, about 122 > degrees Fahrenheit. When attached to a heat-sink fin, it turns the fan > on when necessary, and keeps it on until the heat sink cools below > about 100 degrees F- around body temperature. This particular switch > is available from Digi-Key for about $9, as Catalog Number > 317-1094-ND.
If you're going to be using solar power for the repeater, it might be just as wise to invest in metal -- more heatsink area and better heatsinking. Like, for instance, the head off of an old air-cooled Volkswagen. If you don't need a fan, and the temperature rise is acceptable.... -- Kris Kirby, KE4AHR Disinformation Analyst
