Repairing Old Fan
Posted 27 August 2007 - 08:05 PM
I've got an old fan (110 V, 2.2 A motor), circa 1960, that I'm repairing for church. It had a 3 speed control which burnt out the minute I plugged it in. I've tested the motor, though, and it's still good. So I'm trying to find a replacement switch, but I can't seem to find anything similar to it on digikey, or MSC, or allied electronics. The old switch is simply a rotary switch with a thick stack of parallel plates behind it. Each of the 3 speed settings on the switch connects to a different plate in the stack. I'm assuming that these varied the voltage? Does anyone know of a place where I could buy a similar control switch?
Posted 30 August 2007 - 07:20 PM
I suspect that the switch is actually switching different values of resistance in series with the motor. This will effectively control the maximum torque of the motor and thereby control the speed.
This technique can only be applied to motors designed for this purpose.
You may have to use a standard switch with external resistances. To find the values of the resistances, may be very much a case of trial and error. I expect that the resistances will need to be larger wire wound resistances so start with a large rheostat or similar to work out the values that give you the right control. Once you know the values, you can calculate the power required and then specify the correct resistors.
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