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So many posts about phase conversion to 3-phase

DFWKen

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#1
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.
 

RandyWilson

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#2
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.
 

JimDawson

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#3
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.
 

DFWKen

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#4
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
 

f350ca

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#5
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
 

Bob Korves

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#6
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).
 

rgray

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#8

Silverbullet

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#9
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.
 

coolidge

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#10
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.
 

DFWKen

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#11
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).
Pricey, indeed! $3,000 for a 10HP. Rotary phase converter is in my future. A 10hp will be much easier and less expensive.
 

DFWKen

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#13
That's not a bad price. Building my own would be near $500 even with a used motor. The 10HP sounds like it'll do the trick. Some sites say 15HP for a 5hp lathe duty application; but the specs seem way over the requirements of this lathe. Maybe they're for 100% duty cycle at max current. (Which I'll never see)

Will look for a motor first. Building appears simple. I have experience re building up to 50hp a/c compressor controls. The required components look very familiar. ;)

So I think I have a plan. Excited about stepping up to a nicer economy lathe from my old Chinese 10 x 36.
 

coolidge

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#14
By the way American Rotary told me I'd need 30 amps of single phase for the 5hp RPC I purchased, which I have, but how much are you going to need for a 10hp, just thought I would throw that out there.
 

NCjeeper

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#15
Going to be running mine off of a 50 amp circuit that have for my welders.
 

coolidge

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#16
Speaking of electrical which always drains my wallet my new 3ph band saw requires a 3ph 20 amp Square D breaker...which cost me a whopping $99 from American Rotary dang! I thought maybe American Rotary was jacking up the price but I ran the part# and that's what it cost elsewhere. :cautious: The 20 amp panel mount receptacle $40, plug end $40, well you get the picture electrical adds up.
 

DFWKen

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#17
By the way American Rotary told me I'd need 30 amps of single phase for the 5hp RPC I purchased, which I have, but how much are you going to need for a 10hp, just thought I would throw that out there.
yeah, 50 amp breakers and #8 wire should do it. All my shop wiring is in metal conduit and the longest run from the sub panel is only like 15'.
 

Ulma Doctor

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#18
as a point of information,
a 7.5 hp RPC would suffice for powering a 5hp lathe
as a matter of fact i have run 10 hp machinery from a 7.5 hp RPC without incident. ( i don't recommend the practice, unless you have large single phase input wiring)
 

ELHEAD

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#19
Bought a static converter off eBay, it came from phaseconverterusa . Suited for my 5 HP grinder. Works great. Wrong item shipped the first time. But customer service was very prompt and made correction in no time flat. Would definitely buy from them again. Oh yeah this only cost appx. $50 last yr.
 

NCjeeper

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#20
Only problem with a static converter is the motor is going to be running at 2/3rds its capacity. That really makes your lathe speeds goofy when trying to get the right feed/speed for a job.
 

ELHEAD

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#21
Maybe I am too pragmatic, but most of us tend to use less than 2/3 of the available power we have.
The trade off, .667 X 5 hp = $50, 1 X 5 = $3000.
Just my thinking.
 

rgray

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#22
i have run 10 hp machinery from a 7.5 hp RPC without incident
I didn't know that was possible. Good to know.
I thought I was being all crazy running 6hp from a 3hp rpc (4 machines) But that's mild compared to what you did.
 

Bob Korves

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#23
I didn't know that was possible. Good to know.
I thought I was being all crazy running 6hp from a 3hp rpc (4 machines) But that's mild compared to what you did.
Are you planning to run more than one machine at a time? If not, you only need a phase converter capable of running the largest machine. The phase converter only needs to handle the load that is running. I think I also recollect that turning on additional three phase machines makes them also act to help build the missing phase, i.e., I think (correct me if I am wrong) that you only need to size a phase converter to run your largest three phase motor, even if you turn on additional machines.
 

rgray

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#25
I think (correct me if I am wrong) that you only need to size a phase converter to run your largest three phase motor, even if you turn on additional machines.
I've had it told to me that if you have a 3hp rpc and start your 2hp mill, you can now start up a 5hp load.
I don't think you can work with them both under load only one (either) course if you were running the mill you wouldn't start the 5hp unit, but if running the 5hp unit you can't unless the mill is running or you name is Ulm Doctor (jealous teasing)

The old school thinking is get a 20-25hp rpc and you can run a 10hp motor. The guy I got my mill from spent thousands of dollars having a 25hp rpc put together to run the mill. He never got it finished and I bought the mill from him and have been running it for years on a 3hp rpc. (2hp bridgeport)

I think your thinking is the best idea (size the converter to the largest load)
 

rgray

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#26
I bought a 3 phase panel so I could run the lathe, Mill and power feed for the radial arm saw.
Nice one. I notice the specs say single motor start 5hp total motor run 15hp.
Wonder if they are just being conservative on the starting spec.
 

Reeltor

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#27
I have a 15hp rotary phase converter. I don't need one that large but I came across a NOS 15hp motor for $130. I bought the motor and then the phase converter electronics box. It was easy to mate the box to the motor and then to the machines. Getting the motor locally will save you a ton of cash. I think the 15hp box was only $200 when I bought mine. You should be fine with a 5hp RPC or if you wanted some cushion then get a 7.5 or 10hp.
I went with a RPC instead of a Static Converter, I didn't want to de-rate the power to the motor.

WNY Phase Converters---http://phaseconverterusa.com/Standard-Series_c_27.html
 

Ulma Doctor

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#28
just to be clear,
a phase converter, is responsible for getting the intended motor fired off.
some brands will use potential relays others do not.
the potential relay type use potential relays and start capacitors to send a heavy DC boost, in addition to single phase supply of sufficient capacity, to get the 3 phase motor to turn on
these type of converter will send a boost of DC power every time the voltage or current drops below a predetermined threshold.

once the 3 phase motor is turning and has single phase supply, it will create the third leg of power through winding induction of the spinning shaft.
the third leg is lower voltage and electrically retarded in relation to the other 2 phases of supply.

once a 3 phase motor is fired off and it's output is combined with other 3 phase motors, the total 3 phase circuit is stronger and helps compensate for the phase lag
the RPC is merely an extension of the concept , run a motor on single phase to generate 3 phases and operate other motors form the strength of the combined generative capacity
 

ValveInHead

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#29
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.
 

bobshobby

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#30
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.
I have heard that if you put a decent sized (heavy) pulley on the 3 phase converter motor it will help with starting load.