Motor Speed Control

[Emesine]

I currently have a Baldor KL1205a motor installed on a machine. This is a 1/3 HP 230VAC single speed motor with a start capacitor on a centrifugal switch.

I need to convert this to a variable speed motor. What is the easiest way to do this?

I can access the wires to the start capacitor phase very easily. My first thought is to wire the start phase to a separate power supply, then turn on this phase during only the first 500 ms of starting up the motor. Then control the speed there-after using a simple triac controller (Nimbus, made by control resources, is what I have in mind.)

Thanks!

 

[duke37]

This is a messy way of doing it and is likely to be unsucessful. An AC motor is designed to run at a certain speed depending on the mains frequency. Throttling the input may involve extra current and poorer cooling.

The modern way is to use a three phase motor driven with a variable frequency and voltage. Convertors will operate from single phase.

 

[Minder]

Agree, 1ph cap start induction motors tend to drop out of run at low rpm and/or on load.
Especially a Triac controller would not cut it.
You could go with a DC T.M. motor and controller, although being much larger, torque wise, it would be physically smaller than your 2pole 1/3rd HP motor.
Another alternative is a smaller DC motor and one of the Really cheap 555 based PWM DC motor controllers on ebay.
M.

 

[Emesine]

Thank you both, you've answered my question.

In order to find a replacement for this motor, I need to look at the frame type and the mount type, is this correct? I'm attaching the data sheet for the currently mounted motor for reference. 56c frame F1 mount, I believe.

thank you again for your help,

Agree, 1ph cap start induction motors tend to drop out of run at low rpm and/or on load.
Especially a Triac controller would not cut it.
You could go with a DC T.M. motor and controller, although being much larger, torque wise, it would be physically smaller than your 2pole 1/3rd HP motor.
Another alternative is a smaller DC motor and one of the Really cheap 555 based PWM DC motor controllers on ebay.
M.

 

[Minder]

Also shaft size is sometimes an issue, another option is to get another face mount motor and make up a mounting flange to suit.
M.