Christopher Tidy wrote:
Jon Elson wrote:

Gary Wooding wrote:

A friend has acquired an elderly lathe with a dual-wound 3ph motor.
It has 6 wires going in to it, and is intended for 415v 3ph UK
supply, but he only has a normal single phase 240v domestic supply.
He has been told that he cannot use a single to 3ph VFD with
dual-wound 3ph motors. Is this true? If so, why?

What does "dual wound" mean? Is this a dual voltage motor, or a
two-speed motor?


Probably a two-speed motor. Brook Motors of Huddersfield made a lot of
these for machine tools in the 1950s and '60s. My power hacksaw has a 1
3/4 hp motor with two completely separate windings (a four pole and a
six pole). I opened the motor, cut the star points and brought out all
twelve wires so I could run in on 240 V. Then I built a static phase
convertor with a changeover switch. I can switch speeds while the
machine is running, but the friction in the belt drive means that it
nearly stops in the process. I seem to recall someone saying that
switching from one speed to the other was the problem with using a VFD
on a two-speed motor. Perhaps someone could confirm this?
I can't see any reason why a two-speed motor would be a problem.
One thing is you don't want to flip any switches that are between the
VFD and the motor when it is running. So, always stop the VFD before
you throw the speed switch. The spark at that switch could pop the
VFD.

Jon