I've got a lathe that runs on 3-phase power but my home obviously has single phase. The lathe came with a power supply separate from it that looks home made. It has a 220 volt motor hooked via v-belt to another motor which is 3-phase 440 volt. How do I use this setup? There are no wires connecting this power supply to the lathe motor wires. Can anyone help?

  • Does the motor and generator have ID tags on them, if so please post that info. Dec 25, 2016 at 23:43
  • Do you have a nameplate for the lathe for that matter? If so, can you post the info from it? Dec 25, 2016 at 23:49
  • Probably should have asked the person it came from? Likely the wires that would connect the two were removed to make it easier to move. And yes, it's a rotary converter, which will get you lots of web-pages, some percentage of which will be wrong, but you should be able to find a consensus and infer that it's right.
    – Ecnerwal
    Dec 26, 2016 at 4:03
  • He describes an M-G set, which falls short of even being a rotary phase converter. An entirely different and truly majestic machine is the rotary converter, a rotary transformer whose secondary is DC, and 100%+ power factor. Dec 26, 2016 at 6:47

1 Answer 1


You likely have what is known as a three-phase rotary converter. A quick google search will present uncounted returns for various designs. A friend of mine had one that required a kick-start in order to operate. He had a flywheel attached to the 220v motor which when switched on would not rotate until he struck it with his foot. Once up to speed, it then provided to the lathe motor the necessary power configuration to operate.

I would not begin to suggest that your configuration matches his, as his was home-spun and created without access to the internet! The links I've found have variations which may be challenging to match to yours.

One option you have is to replace the rotary converter with what is called a VFD converter. It is going to be a simpler device, with the added benefit of speed control as well as likely a more reliable bundle for your application. Unfortunately, it is an additional purchase, while you already have the devices on hand for the rotary phase converter.

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