dimmer vs. fan control

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fireryan said:
Does a fan control vary frequency and a dimmer vary voltage? And can you use a fan control on a small motor.
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It will work for a while and then burn the motor out.

A fan on our fireplace was controlled with a dimmer switch. Although it did last several years, it still cooked the motor eventually.

Since electronics have become smaller over the years, I can see how it is now possible to put a VFD into an area the size of a switch.
 
K8MHZ said:
It will work for a while and then burn the motor out.

A fan on our fireplace was controlled with a dimmer switch. Although it did last several years, it still cooked the motor eventually.

Since electronics have become smaller over the years, I can see how it is now possible to put a VFD into an area the size of a switch.
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So you are saying I can use a fan control for a small motor but not a dimmer?
 
fireryan said:
So you are saying I can use a fan control for a small motor but not a dimmer?
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Well, it depends on the motor.

Inductive motors are set to run at a fixed rate of speed which is a multiple of 60 Hz with some allowance for slip. If you slow the rotor down you must also reduce the frequency that the AC is running at. If that is not done it reduces the REMF generated by the rotor and the energy that is not canceled out turns to heat. Sometimes lots of it.

In a nutshell, to control the speed of an inductive motor both the voltage and frequency has to be reduced.

Motors with brushes, usually labeled as AC/DC motors do not have that requirement and can be controlled by a reduction of voltage only.
 
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