# New lathe.



## bigman1 (Jun 1, 2014)

Hi folks,
I would like to buy a larger lathe,most bigger one's run on 3 phase, only power i have is a Trace 24v/240v power inverter that will go to 6000 watts for about 10 mins. What would be the largest 3 phase motor that the inverter would run using a phase converter. Thanks. Ronnie.


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## xalky (Jun 1, 2014)

Ummm, I don't think a power inverter is what you want to run a lathe. You need a 3 phase converter. Am I missing something?


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## John Hasler (Jun 1, 2014)

bigman1 said:


> Hi folks,
> I would like to buy a larger lathe,most bigger one's run on 3 phase, only power i have is a tthat will go to 6000 watts for about 10 mins. What would be the largest 3 phase motor that the inverter would run using a phase converter. Thanks. Ronnie.



I don't think your inverter will start a motor larger than about 1HP (f that).  The manual may tell you how large a motor you can run.

[Edit]
You might want to consider buying a lathe with no electric motor and then rigging a gasoline engine to drive it.


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## JimDawson (Jun 1, 2014)

Bring a bit conservative and this is a reasonable guess.  Maybe you could run a 4 HP motor for about 10 Minutes, but you may not be able to start it.  You have the losses in the phase converter, and additional losses in the motor.  And the start load is about 3 times the run load

6000 Watts / 240 V = 25 Amps intermittent available output

I would say you might be able to start and get reasonable run time with a 1 HP (0.75 KW) motor.  In that case a single phase motor would be better. about 14 amps at full load.

You may be able to run a 2 HP (1.5KW) 3 phase motor from a VFD if you set the startup ramp long enough that it doesn't overload the inverter on start up.  This would run at about 16 amps at full load.

A 3 HP (2.2KW) , 3 phase motor/ VFD would run at about 27 amps at full load.

Overall I would say your power situation precludes anything too large.

EDIT:  I like John's idea, a gas or small diesel engine would be a good option.


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## bigman1 (Jun 2, 2014)

Hi,
Thanks to all for your valuable help,i think i will go down the I.C.engine road.
Thanks to all,God Bless. Ronnie.


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## thenrie (Jun 2, 2014)

I just went through this and went over all the options. I decided that for my lathe (a Delta Rockwell 11X36), which has a continuously variable Reeve's drive, that a rotary phase converter was the best option for me. I paid $150 for a used one with a 3hp 3-phase motor. You can make one yourself very easily.  My lathe has a 1hp 3-phase motor and the 3hp rpc is more than adequate. An additional benefit of the rpc is that you can run multiple machines on one rpc, such as a lathe and mill, or even a 3-ph table saw. In fact, you can run several simultaneously, within limits of current and hp rating.

A VFD offers variable speed (which I didn't need) by varying the current frequency to the motor. It is more expensive than a rpc and it can only be used on one machine. Also, you can overheat your lathe motor with a VFD by operating it at speeds below which it is designed to operate, unless you install an auxiliary fan to cool it, although, by most accounts this is a minor worry unless you use your lathe long hours a day. Additionally, with my rpc, my lathe's speed ratings posted on the plaques are correct, while if I used a VFD I would have to install a tachometer to know precisely the speeds the lathe was turning. If your new lathe does not have a vari-drive, like mine does, and requires stopping the lathe to change speeds, a VFD may be the way to go.

For a rpc, choose a 3-phase motor with the same or greater hp rating as your lathe. It should be rated for the same voltage as your single-phase power source (mine was 220v), and the lower the rpm rating the better (1725 vs 3450), since the higher rpm is louder and it will be running continuously. You can simply wire it to your single-phase power source, then to a properly rated switch, and out to your motor. With this simple setup, you can start the rpc motor with a rope to get the rpc turning, after which it will run on the single-phase power, while re-configuring the power to 3-phase and passing it on to your lathe motor via the power switch. You can also add a pony motor (such as a washing machine motor) or in-line capacitors and a starter switch to make the rpc self-starting. Not hard, nor technically difficult, and there are plenty of sources of info and plans on the Internet.

Good luck.


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