Quote:
Originally Posted by upallnight
If you run the blower at a low speed I think you will use the FSR more since more of that energy is converted to heat, whereas if you run the blower at a high speed less of the current is converted to heat by the FSR, but since the blower motor is spinning at a faster speed, the blower motor will expire quicker.
You choose what you want to replace. Blower motor of FSR. If I don't need to run the blower motor I just keep it off.
|
Neither the FSR nor the blower motor are pure resistors, but they can be considered close enough for this analysis. Maximum heat dissipation in the FSR will actually occur when the voltage drop across the blower equals that across the resistor.
So when the blower is set for low power, the FSR is set to a high effective resistance and the current is low - so the blower spins slow and the FSR does not dissipate much power due to low current.
When the blower is set for high power, the FSR acts as if it has low resistance, so the current is high - the blower spins fast and the FSR does not dissipate much power due to low resistance.
A little circuit analysis and basic calculus shows the max power dissipation when the FSR resistance is in the middle. If they were pure resistances in series, it would be when R_FSR = R_blower, which would also be when V_FSR = V_blower.
So no need to worry about your fan idling at low speed. Or at full speed.
Here's a theory about why some FSRs fail quickly while others last a long time ... a weak/failing blower motor will stress the FSR. If the blower motor spins slower than it should due to mechanical problems or increased internal resistance, then the back EMF will be smaller than it should be. So the current will be higher than it should be. So the FSR will have more energy to dissipate.
So if you keep blowing FSRs, there could be a problem with the blower, either electrical or mechanical.