I'm not sure if it's OK to run this type of motor at different voltages. I know that most (if not all) DC motors run fine at different voltages. A major part of my job is SCR systems for controlling 1000 HP DC motors.
AC motors can't be controlled like this. An AC motor's speed is determined by frequency (60 Hz standard in US) and number of motor windings. Many industrial applications use VFD technology (variable frequency drive) to control the speed of AC motors. But your electric fans in your house just tap power into a different motor winding to slow it down.
If it's OK to do this, then you should check out how the blower motor for your heater is wired. You'll see that it has a resistor in line with the power to the motor. For each fan speed there is a wire coming from the switch that taps the resistor in a different place. For low speed the power comes in through the end of the resistor so it gets full resistance and lowest voltage to the motor. For medium it taps the resistor somewhere in the middle so it only gets partial resistance for somewhat higher voltage. For high speed it bypasses the resistor completely and feeds full voltage to the motor.
You could wire it like this if the motor will accept it. No diodes required.
Personally, I prefer manual control of my electric fan. I don't have to worry about a thermostat turning the fan on while I'm working on something. When the temp starts to rise while in traffic I turn it on. I always leave it off while cruising on the highway.
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My Elky Page Updated 7-21-00
"Think for yourself. Don't let popular opinion make your decisions for you."
Chad Landry
TC Member #643
'68 El Camino
[This message has been edited by cjlandry (edited 02-05-2001).]
AC motors can't be controlled like this. An AC motor's speed is determined by frequency (60 Hz standard in US) and number of motor windings. Many industrial applications use VFD technology (variable frequency drive) to control the speed of AC motors. But your electric fans in your house just tap power into a different motor winding to slow it down.
If it's OK to do this, then you should check out how the blower motor for your heater is wired. You'll see that it has a resistor in line with the power to the motor. For each fan speed there is a wire coming from the switch that taps the resistor in a different place. For low speed the power comes in through the end of the resistor so it gets full resistance and lowest voltage to the motor. For medium it taps the resistor somewhere in the middle so it only gets partial resistance for somewhat higher voltage. For high speed it bypasses the resistor completely and feeds full voltage to the motor.
You could wire it like this if the motor will accept it. No diodes required.
Personally, I prefer manual control of my electric fan. I don't have to worry about a thermostat turning the fan on while I'm working on something. When the temp starts to rise while in traffic I turn it on. I always leave it off while cruising on the highway.
------------------
My Elky Page Updated 7-21-00
"Think for yourself. Don't let popular opinion make your decisions for you."
Chad Landry
TC Member #643
'68 El Camino
[This message has been edited by cjlandry (edited 02-05-2001).]
