cheapest speed control possible for 115v AC 1/4-1/2 hp fan motor

[zane]

Hi,

I need to control the speed of a 115v AC 1/4-1/2 hp fan motor, or something like a fan motor, for a project I'm doing. I almost got a variable speed controller for a router but then someone stopped me because they only work for brush type universal motors. And will not work on induction, shaded pole, soft/slow start, or brushless type motors. As far as what will work for the motor I need I have not been able to figure out. Any help would be greatly appreciated. Thanks!

 

[marke]

Hello zane

 

Welcome to the forum

 

Standard induction motors can only be speed controlled by frequency variation. High slip induction motors can however be speed controlled by varying the voltage. These high slip motors are sometimes used in fan applications where the motor is an integral part of the fan.

By reducing the voltage, the available torque at the motor shaft reduces. When the available torque is less than that required by the load, the load will slow down. With a fan load, the torque reduces with speed so an equilibrium will be met when the fan torque equals the motor torque.

If you try this with a standard motor, you will have very high currents and slip losses which will cause the motor to fail early.

Provided that the motor is a high slip motor, you can use a triac based voltage ontroller, or a transformer to reduce the voltage.

 

Best regards,

[Push_Luck]

Hello zane

 

Welcome to the forum

 

Standard induction motors can only be speed controlled by frequency variation. High slip induction motors can however be speed controlled by varying the voltage. These high slip motors are sometimes used in fan applications where the motor is an integral part of the fan.

By reducing the voltage, the available torque at the motor shaft reduces. When the available torque is less than that required by the load, the load will slow down. With a fan load, the torque reduces with speed so an equilibrium will be met when the fan torque equals the motor torque.

If you try this with a standard motor, you will have very high currents and slip losses which will cause the motor to fail early.

Provided that the motor is a high slip motor, you can use a triac based voltage ontroller, or a transformer to reduce the voltage.

 

Best regards,

 

Could you help me, please... how if i want to control the induction motor using PLC. i have no idea how to start it... so i hoe you can give me some outline on doing the task. Thank you. If other have idea about ti, please share with me. thanks.

 

[jraef]

Could you help me, please... how if i want to control the induction motor using PLC. i have no idea how to start it... so i hoe you can give me some outline on doing the task. Thank you. If other have idea about ti, please share with me. thanks.

 

I answered you in your other posting.

[zane]

Hi,

 

I tried a triac based voltage controller and I lost too much torque! And I can't have a capacitor! What should I do?

[jraef]

You need to determine the type of 1 phase motor that you have and post it. Just so you know, some types cannot be used with speed control. If it uses a capacitor that is switched out with a speed switch, you will NOT be able to control the speed of that motor. Those types are called Split Phase, or Cap-Start / Cap-Run, or Cap-Start / Induction run. Read this article if you are not sure.

http://www.iprocessmart.com/leeson/leeson_...ase_article.htm

[marke]

Hello zane

 

If you were not able to control the torque, then you do not have a high slip motor and you can not control by voltage control only.

 

There are a limited number of variable frequency drives available for single phase motors, but the motors that can be used are very restricted.

The best way to gain good control, is to replace the single phase motor with a three phase motor and use a single phase input, three phase output variable speed controller. Unfortunately, this costs more than a triac based controller.

 

Best regards,