240v Motor Speed Controller - Advice required

[Shox Dr]

Is that true with a 3 phase motor too? I don't mind losing torque when its turned down.

Ta Al

What you need is a VFD, it controls speed by altering the Hz, dependant on type you can set the amount of Torque. The same as I have but for 3ph in 3ph out

 

[Luke]

Al,

Have a look at the Inverter Drive Supermarket - same people as linked to before. You will need to now the size/power of your fan/motor to size a suitable inverter.

A 10k pot will give you control of setpoint frequency, or you can usually set most inverters up with a number of speeds on a selector switch/switches - speed 1 = 10 Hz, speed 2 - 34.5 Hz etc as you wish.

Luke

 

[tigler]

It will, however you will lose all torque

Some torque , but not all. It will only be an issue at very low speed. It's been fine on the applications I've tried , pumps , fans and small process drive systems.

 

[Pete.]

For future ref , with single phase induction motors a light dimmer can be used to control speed !! I've done this a few times with low powered motors.

Have you got any details on that Tigler? How can one tell if they have a suitable motor?

 

[tigler]

As far as I know any low powered , single phase induction motor is ok. Largest motor I've tried is about 800 watt's , so around 1 horsepower. Just bought a normal domestic light dimmer from a DIY store , I think it was a 1KW version.

 

[Pete.]

So you just wire the dimmer in series with the motor switch? I have a .75kw motor on my mill that I'd like to be able to slow down. It's a cap start cap run far as I know.

 

[Shox Dr]

Pete. I will not work fella, you WILL lose all torque esp' in the application you are using it for.

read this thread on how I got on. It will save you a lot of grief

 

[tigler]

So you just wire the dimmer in series with the motor switch? I have a .75kw motor on my mill that I'd like to be able to slow down. It's a cap start cap run far as I know.

All I can say is try it and see. Dimmers are cheap as chips and if the torque is reduced too much you haven't lost much !!
You just connect the motor to the load terminal on the dimmer , that is the terminal the bulb would be connected to if it was used as a dimmer.