AC Phase controlling by Triac for AC motor speed control

[chanoknun108]

I have to regulate the speed of single phase AC.

Frequency variation method is very suitable for 3 phase motor but it might not be good for my single phase motor because my motor uses capacitor start and capacitor is frequency sensitive element.

Now, I am thinking about using phase controlling method by using power triac. If you have any experience about this method. Please share your experience.

Is it good method for AC motor speed control?
Is there any problem using that method?
Other suggestions?

Thank you very much.

 

[gerty]

If you have a centrifugal start switch inside the motor you won't be able to slow the motor down much because it'll kick in and connect the start windings.. :cry:

 

[stevez]

Most AC motors run at synchronous speed (minus some slip unless it's a synchronous motor). A reduction in supply voltage may produce a change in speed however the motor will not behave as you'd like and will soon overheat and fail. This applies to single and 3 phase motors.

There are some smaller single phase motors - I think 'universal' is the correct term - that behave more like a DC motor - RPM changes with voltage and within limits voltage or power reduction is an acceptable means of speed variation.

If you would use the triac to chop or cut off the AC supply the net effect would be a reduction in RMS voltage or total power to the motor. If it's a universal motor AND the torque required by the load can be maintained this method will probably work. If the AC motor is not universal it probably won't work.

I would think that triacs would be a part of a VFD but I don't think that's what you intended.

 

[fixitguy]

If there is a centrifugal switch in your motor, it will activate when the speed drops below 33% of the rated motor speed. If this happens, it is probable the motor will burn-up. However, if the AC motor is an induction motor and is being used on a fan to move air, you can go to the wal-mart or home depot and buy a fan control (used on ceiling fans). Take your motor info with you so you can determine if the control will handle the load of your motor.