So many posts about phase conversion to 3-phase

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.
 
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.
 
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.
 
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)
 
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.
 
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
 
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
 
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.
 
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.
 
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