Quote:
Originally posted by jaydee116
You have to think backwards with rheostats. The more you turn it down the more load it is handling. The higher you run it the less load it is handling. Or maybe I just missed something...:shrug:
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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.