2 speed 3 phase motors question

[minilathe22]

If I have say a 4 pole induction motor (3 phase) is it possible to rewire it into a 2 speed motor, by joining up the coils inside such that they pair up and the motor becomes a 2 pole or 4 pole motor, depending on a switch. This would be very handy for my wood lathe, I am just curious whether this can be achieved, or whether a 2 (or more) speed motor has to be built with this in mind from the beginning?

I am assuming that a) this type of motor can only have an even number of poles (I have only seen small DC motors with an odd number of poles)
and b) the example 4 pole motor cannot be wired to have more than 4 poles?

2 speed motors do come up now and again but not often!

 

[flh801978]

It would be very difficult to open up a 4 pole and rewrire into 2 pole so as you say these type of motors need to be built like that from the start
Why does you lathe not go fast or slow enough?
You can run a 4 pole at 100 htz so 2800 rpm
But if you have a 2 pole it may not like being run at 10 htz

Ian

 

[minilathe22]

I currently have a 4 pole motor on a VFD, although it is an older motor so will not have been designed with VFD in mind. I would like more torque at low speeds for large bowls, and some higher speeds for final sanding. I think I will do more research on adjusting my VFD settings, currently with the 4 speed pulley setup to the highest speed, the motor speeds up and then slows down, as though it does not have enough power. I think I limited it to 75Hz. Will older motors work ok at 100Hz? I assume it will not have much torque?

 

[flh801978]

I have 2 graduates long bed and short both with vfd’s and run them from 10hz to 120hz with no ill effects
Remember the important bit in a motor is the same whether 2 or 4 pole ( the rotor) so that is happy spinning at 3000rpm
Th only proviso is that i wouldn’t run at 10hz for long

Ian

 

[minilathe22]

looks like me vfd settings for higher frequencies need adjusting then. Thanks.