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Old 09-24-2003, 09:22 AM
tower tower is offline
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Join Date: Aug 2002
Posts: 179
response to tkamiya

So if that is the case, why does mb put a 30amp fused circuit with the resistor in series and only a 15amp fused circuit without the resistor in series. (Hint, the answer is in the whole circuit load, not the load of the fan itself ie. power requirements.)

Maybe a bit more. As I understand it. Putting the fans to a lower speed essentially makes the windings of the motor behave more like an electric heater. As the fan slows, the windings behave more and more like a direct short because you have not removed the energy via motion of the fan. Energy cannot be created or destroyed, so it heats up, effective motor winding resistance decreases causing the current load to go up. So...the massive resistor in series works as a current limiter. In the worst case, if the fan is stalled, all the energy is dissipated as heat in the resistor, not in the electric dc motor. No fryed motor....

Last edited by tower; 09-24-2003 at 09:30 AM.
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