Newbie- Variable AC speeds for a grinder motor ? - how...

[nick mulder]

Hello,

I have a 2200w grinder motor (240v, 50Hz) here which I would like to be able to run at different speeds - i.e. from zero up to its full supply rpm...

If this were a DC motor I'd simply tap some of the voltage off elsewhere or get more sophisticated with PWM etc... But with AC I dont know what is going on... does the motor run off the frequency of the supply and lowering the voltage would simply reduce its torque ? or ?

Basically its a one off application with time constraints, what simple method could I use ? I'm hoping a simple AC 'dimmer' circuit will do it

...there are two wires coming out of it now that I have removed the trigger

any help appreciated,
Nick

[Al_The_Man]

If this is a 1ph split phase induction motor there is not much you can do to vary the speed.
If it is a 3phase motor, then you can run it with a VFD.
Conversely you could replace the 1 phase motor with 240v 3 phase motor and run the VFD off of 240 1 phase in.
Al.

[vger]

Grinder motor? Angle grinder? Bench grinder? A bit more info would help. Al is correct about the split phase induction motor. Not much you can do with it. If by chance you are talking about an angle grinder (has brushes) then the dimmer may work if you can find one that will handle the power (at least 10 amps).

Steve

[radioactive]

As Al said, if it is a 3 phase then a VFD is the answer. I run a 3 phase 1 hp grinder in the garage with a VFD and it works excellent... Currently it is running with a Hitachi 3 hp VFD but that will be used for my milling machine shortly, so I am replacing it with a Teco FM50 rated for 1 hp, it was $127 including shipping from FactoryMation.com