Variable 3 Phase to run off 240v


Thread Starter


I have little knowledge about the proccess of 3 phase motors, but I do know that to buy a ready made system cost way too much for me. Basically what I would like to do is: Have my 3 phase motor operate my lathe with variable speed control, and do this from a 240v power supply. Please help, it will save me a fortune... PLEASE
Firstly, the 3 Phase motor must have a rating label on it some where, have a look and see if it has a voltage rating which resembles the following

220 - 440 V ac 50/60 Hz

If so we are already on a fairly sucessful path, if so I will assume that it has been running on 415Vac
next is the KW rating of the motor, this will be your other limiting factor, 7.5 Kw would be the ultimate upper limit I would imagine, as from experience this from memory was about the largest Single Phase to 3 Phase VSD (Variable Speed Drive) that I could obtain.

If the above criteria have been met then we will have a look at the terminal configuration of the motor.

1) undo the terminal box cover
2) make a Drawing of the configuration.
3) have a look on the reverse side of the terminal cover lid to see if it has a diagram.
4) If it has a diagram they normally show two configurations, each one identifyed by two symbols, the symbols are knowen as STAR and DELTA, Delta is the one that looks like a triangle.
5) you should change the links to resemble the Delta Diagram, this will allow the motor to run on three Phase 220-240Vac.
6) obtain a Single Phase to Three Phase VSD and hook it up to your Motor,
7) You should really take it to your local Electrician to have it hooked up to the VSD

If you dont have a Diagram under the terminal box lid, Email me and I can send you a couple of photos.

Email [email protected]

Bob Peterson

This is not really a do-it-yourselfer type forum.

We can point you in the right direction, but if you are not qualified to make the right decisions along the way, you could have big problems down the road.

Having said that, many VFDs can be powered from single phase 240V and power 3 phase 240V motors. Normally substantial derating of the VFD is required.

Steve Myres, PE

It sounds as if you want to run a three phase lathe on single phase, and to have variable speed as well (doesn't the lathe have mechanically vaariable speed?). You could do all this with a VFD or variable frequency drive, and you can get used or surplus ones for pretty cheap (be sure to oversize vs. the motor size because of the single phase feed). But this kind of work is potentially very dangerous, and you should get someone to help you who knows what they're doing.

Servo Wizard

I'm assumming that you have single phase service and a 3 phase motor. If that is in fact the case then there's a solution that will make that combination work. The typical phase converter has been up staged by the variable frequency drive, aka VFD. The VFD can be powered by single phase service and output true 3 phase plus you can vary the frequency to control your motor speed. The compromise is that you have to derate the VFD by 33% so if you have a 5HP motor then be looking for a 7.5HP+ VFD.