Thread: Running 3-phase gear off single-phase power.

rather than continue to hijack another thread, I thought I would post this as a new topic. I did some research into this when I bought my lathe (actually my wife bought it for me for my 50th birthday, but that involved me doing the choosing, the buying, the drive to Sydney and towing it home, etc...), it's a big machine with a 3hp 3-phase main motor and a separate 1/8hp 3-phase motor for the coolant pump.
There are essentially 3 ways to run a 3-phase motor off single phase input. One is to use a capacitor wired into one leg of the single-phase input, and, via a momentary switch, the capacitor is used as a starter, i.e. the motor is switched on via a normal on/off switch and the momentary switch is held for about half a second to start the motor, then the motor continues to run on 2 of the 3 legs. This works in low-load situations, the motor will only produce 2/3 of it's rated power. I've wired the coolant pump motor on my lathe this way. There are diagrams for this readily available on the web.

Another way is with what's called a 'rotary phase convertor', this uses a separate 3-phase motor as an idler which, by powerful white-man magic, produces the third phase. The idler motor is generally started with a capacitor as above, or in really basic setups can be pull-started with a cord like a mower. Rotary convertors can be set up as a plug-in, wheel-around unit with a 3-phase socket (or several) that you can plug any 3-phase machine into, or multiple machines up to it's rated output. No alteration is necessary to the machine itself. These are available as commercially produced units; in fact, a good friend of mine has just established a business manufacturing these units for domestic and commercial applications. A machine plugged into one of these units will behave exactly as if connected to 3-phase mains power.

A third way is to wire the 3-phase motor via a Variable Frequency Drive (VFD) as mentioned in another thread. Like this one (incredibly cheap): eBay Australia: Buy new & used fashion, electronics & home d

These units can only run one motor, and if running an existing machine, like my lathe, from a VFD the machine has to be re-wired so that the single-phase input goes into the VFD input, the VFD output goes directly to the 3-phase motor, and all switching is done via the VFD. I stripped all the 3-phase wiring out of my lathe and re-wired the machine so that the original switches now act as controls for the low-voltage switching circuitry of the VFD. You can't just set it up to plug a machine into, as you can't have any switching between the VFD's 3-phase output and the motor. A benefit of the VFD is that it provides a speed control for the motor, which is a boon on machines like lathes and big drill presses etc.

I'm surprised more people with home workshops aren't aware of this stuff. My neighbour sold his 3-phase lathe when he moved here as he couldn't run it, he was spewing when I showed him my 3-phase lathe running off single-phase power. Again, there's heaps of info on all these methods on the interweb.

Originally Posted by rovercare

Phase convertors are the best, you can buy one just up the road in longwarry

A mutual friend also makes them in Drouin Matt.