Quote:
Originally posted by Since87
If the fan was simply a resistor (electrically), the most power the rheostat could dissipate would be 1/4 of the fan's 12V power dissipation. (Google "Maximum Power Theorem")
The maximum dissipation would occur when the voltage to the fan was at 1/2 of the total voltage. At this point, the current through the fan would be 1/2 the current at full voltage and the fan power dissipation would be:
1/2 * 1/2 = 1/4
Same for the rheostat.
Fans do not behave exactly like resistors though, so some margin is in order. I agree with Ben's suggestion.
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I spent several months messing with pots and any fan rated over the pot makes the pot fry when the pot is turned down. The more you turn the pot down the hotter it gets. I fried several 3watt pots on 5watt fans when turning them down. I I run the pot wide open then the pot works fine at ever tripple the rated the fan. The pot is doing all the work not the fan.
Give it a shot and you will see what I am talking about. I know your an electronics guy but this is just my experience. I got 15 dead pots to prove it.
Sparked: here is the identical pot as that one from frozen for $1.50.
http://www.allelectronics.com/cgi-bi...-15&type=store