AC speed controller

[Shadow]

Does anyone know how I can make a speed controller for an AC moter.
It works on 230V with a current of 0.17A and a power of 39W.

 

[Ravi]

Hi shadow,

The easiest way of electronically controlling the power feed to a motor is via solid-state thyristor devices such as SCRs or triacs. I'm giving you a simple ckt built around a SCR. Control element is SCR which feeds 1/2 power to the motor (this results in only a 20% or so reduction in maximum available speed/power), but in the off 1/2 cycles the back emf of the motor is sensed by the SCR & used to give auto adjustment of the next gating pulse,to give auto speed regulation. I do not know what your requirement is but this ckt provides a high torque under low speed conditions. Hope this will help you

 

[stevez]

Only some AC motors can be controlled by the simpler methods - chopping off part of each cycle. Many AC motors do not respond well to this and require full voltage - to adjust the speed of these motors requires that the frequency be varied.

 

[Shadow]

Thanks, but I mean so I can control the speed with a potentiometer.

 

[stevez]

The RPM of many AC motors is linked to the number of poles and the frequency of the supply voltage. In order to reduce the RPM the frequency must be reduced, not the voltage.

Some of the simpler speed controls (using a pot) do not vary the frequency but rather chop the waveform so that the RMS voltage or total power is reduced. Some universal or similar AC motors are voltage dependent and can be controlled this way - many are not. My only concern is that the motor is compatible with the method being used to reduce the RPM.