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?

Chris