AC motors (1 ph to 3 ph) question.

[umnik]

I was told that some 1 phase induction motors are actually 3 phase motors, but wired in special way plus capacitors, so they run on 1 phase circuit, thought at lesser power. Is it true? How can I figure it out?
The context for my question is following. In my Delta Drill press I have 3/4 HP, 1 PH motor, 1725 RPM, which can be wired either for 110v or 220v . I want to use VFD to control the motor's RPM, but for that I need 3 phase motor. If I can reuse my current motor, that would be great, otherwise I will just get a new motor for that purpose.

 

[CluelessNewB]

Short answer no you can't use your current motor.

Your motor is most likely a capacitor start single phase motor with a centrifugal switch to disengage the starting winding when the motor gets up to speed. If you were to try and slow it down by reducing the frequency the starting winding would kick back in as the motor slowed. The staring winding and associated starting capacitor are not designed for continuous operation and would quickly burn out.

 

[jim18655]

He doesn't want to use the motor on 220v with a VFD, He wants to know if the motor can be re-connected internally to make it a 3 phase motor. I'm not a motor rewinding expert but I would think the winding arrangement would be wrong.

 

[JimDawson]

I was told that some 1 phase induction motors are actually 3 phase motors, but wired in special way plus capacitors, so they run on 1 phase circuit, thought at lesser power. Is it true?

Whoever told you this might have been confused by running a 3 phase motor on single phase. That is possible with some capacitors, but not the other way around.

Bottom line is that you have to start out with a 3 phase motor. You will have to get a 3 phase motor if you want to run your drill press on a VFD.

And for that application, I would recommend a sensorless vector VFD, much greater speed range with nearly constant torque over the speed range.

 

[umnik]

It is not confusion. The point is that some chinese machinery equipped with such 3 phase motors. May be some manufacturers have access to cheap 3 phase motors and they just used capacitors and "magic" wiring to run those motors on 1 phase circuits. Sure the motors run inefficiently, but work. I thought that I might drill press equipped with such motor. In that case I could just revert back it to 3 phase.
The question is how can I distinguish such motor from true 1 phase motor.

 

[Ulma Doctor]

there is no magic to running a 3 phase motor on single phase supply, RPC's do it every time they operate.
the 3rd phase is generated by induction of the spinning rotor inside the windings ,while single phase power is applied.
some more sophisticated systems will balance the 3rd phase in relation to the other 2, by adding run capacitors

i'm not sure exactly how to instruct you to identify the motor you are describing, but i can give a few pointers that may help

if the motor is dual voltage 460/230, it is most likely a 3 phase motor (single phase motors are generally spec'd as 230vac for high voltage use, 115vac for low voltage use)
if there are 9 wires present for wire up, you may just have a 3 phase motor( it will not run on 115vac)