So many posts about phase conversion to 3-phase

DFWKen

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For the last week, I've been sifting through threads here and elsewhere about running a 3-phase lathe on single-phase power mains. It's making my brain hurt and although I've learned a lot, my concerns are still lingering.

I'm purchasing the Grizzly G0740 3-phase (2-speed) lathe.
  • Adapting a VFD to a 2-speed lathe (especially a brand new lathe) is just too labor and skills intensive. All I really want is 3-phase power suitable for running the 5hp (max) lathe. I don't care anything about frequency control; the lathe is fully adequate in stock condition for my needs. Almost all of the controls would have to be wired directly to the VFD for jog, reversal, speeds, emergency stop, brake, etc. I don't want to butcher the lathe with a whole new control panel.

  • So it appears that a rotary converter is the ticket. The lathe has a 5hp 2-speed motor. I doubt I'll ever use the highest speed at max current draw; so is a 15HP rotary converter really required? The price jump to build or buy a 15HP rotary converter is much higher than a 10HP. Would a 10HP suffice?
  • And finally, doesn't anyone make an electronic phase conversion unit that is straight 60hz to 60hz and simply converts from single to 3 phase? All I want is 3-phase power for the lathe at max 20 amps. I want to keep the lathe totally stock.

  • OH, or maybe simply replacing the motor would be the thing to do. A 5hp 1750 rpm single phase motor would do it, but I'd probably need to change the drive pulley so that the spindle speed range would fall into useable rpm like other single-speed motor lathes.
 
Even if you could find such a VFD, you would have to bypass the lathe controls. VFDs do not take kindly to pushing into a circuit that suddenly goes open; aka hitting the lathe's off button.
 
So it appears that a rotary converter is the ticket. The lathe has a 5hp 2-speed motor. I doubt I'll ever use the highest speed at max current draw; so is a 15HP rotary converter really required? The price jump to build or buy a 15HP rotary converter is much higher than a 10HP. Would a 10HP suffice?

A 7.5 or 10 HP should be more than enough. We have a couple of RPC expert members that will be happy to offer better advice than I can.
 
A 7.5 or 10 HP should be more than enough. We have a couple of RPC expert members that will be happy to offer better advice than I can.

This is such a great source for technical information.
The new lathe's electrical specs are:
Motors: Main Type........................................................................................................................................... TEFC Induction Horsepower.................................................................................................................................. 5 HP / 2.5 HP Phase.................................................................................................................................................... 3-Phase Amps..................................................................................................................................................... 14A/10A Speed..................................................................................................................................... 3450 / 1725 RPM Power Transfer ............................................................................................................................... V-Belt Drive Bearings..................................................................................................... Shielded & Permanently Lubricated Coolant Pump Type........................................................................................................................................... TEFC Induction Horsepower............................................................................................................................................. 1/8 HP Phase.................................................................................................................................................... 3-Phase Amps........................................................................................................................................................... 0.4A Power Transfer ............................................................................................................................... Direct Drive Bearings..................................................................................................... Shielded & Permanently Lubricated

I don't know if a single-phase motor would be reversible (if indeed the stock lathe is reversing via phase manipulation or simply a gear change in the head).

Ken
 
This company makes a solid state phase converter, but they aren't cheap.
http://www.phaseperfect.com/p/t/overview
They run silent, occasionally the 10hp lathe will warm it up and the cooling fan comes on but the surface grinder and Hardinge don't work it hard enough. Up to the current limit they don't care whats connected or how its switched. Same as having 3 phase coming from the panel.

Greg
 
American Rotary https://www.americanrotary.com/ is also a good source of rotary phase converters. Building your own is also a real possibility, and you can save a lot of money that way if you want to supply the time and effort, and is not that difficult. There is help available on this forum for choosing components and tuning it to best match your machine(s).
 
A 10 hp rpc should be right for your 5 hp motor.
 
I went through the same dilemma awhile back. But I decided to build my own RPC, if your only planning on the lathe a 5hp converter should do . But if down the road you add a mill with 2 hp motor three phase you would have to upgrade to a 7 1/2 hp converter. That's why I'd suggest going for a 7 1/2 hp now.
Ulma doctor , on here will help with what you need to build a nice RPC for half or less the price of a new made store bought model. Get on eBay and craigslist Ck for used three phase 7 1/2 hp motor , even if the shaft is damaged you don't need it anyway. Even look for used RPC , they come up on craigslist cheaper at times. But the contactor 3phase, push button switches , 220 start capacitor, some 220 run capacitors. Enclosure box , terminal block , wires , wire glands, on mine I'm using rubber mounts for the motor, and wheels to move it. Not hard to build it , but watch handling the capacitors , they can bite if charged. Lots of the items can be picked up used. I forgot the fuse block and three fuses. I think thirty amps will do for your build but Ck with Ulma he's the pro. If I didn't live so far from him I think he'd a built mine.
 
American Rotary https://www.americanrotary.com/ is also a good source of rotary phase converters. Building your own is also a real possibility, and you can save a lot of money that way if you want to supply the time and effort, and is not that difficult. There is help available on this forum for choosing components and tuning it to best match your machine(s).

I just ordered an American Rotary 5hp the other day.
 
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