74dart

I have heard it can be done but have never seen it done. Can you run 2 3 phase motors on single phase power by wiring them a special way?

jrs_dodge_diesel

Short answer, no. It will not work. 3 phase motors need a 3 phase supply in order to create the rotating magnetic field required for the rotor to spin. If you hooked a single phase line to a three phase motor, it will not spin.

The only way to make it work is to convert your single phase into 3 phase power. One way to do that is to use a rotary phase convertor (RPC). I have little knowledge on those devices other that what they are used for. More info on them can be found here : http://en.wikipedia.org/wiki/Rotary_phase_converter

And on 3 phase induction motors : http://en.wikipedia.org/wiki/Induction_motor

Just curious, what are you trying to run?

Rollin'_Coal

I am an industrial electrician and i work with three phase motots all the time, In theory you can run a three phase motor off single phase. It is unreliable, requires capacitors and relays and resistors, and doesn't make nearly the rated power of the motor. The three best ways to run a three phase motor on single phase power would be;

1. Rotary Phase Converter - a single phase motor is coupled to a three phase motor to spin it like a generator.

2. Static Phase Converter - A capacitor bank is used to cause a temporary phase shift to simulate three phase power to get the motor spinning and then it just runs on single phase power at a reduced rating.

3. a VFD (Variable Frequency Drive) - A VFD converts single phase AC power to DC, It then goes through a three phase inverter and is switched back to 3 phase power and can also be speed controlled by the frequency output of the drive.

74dart

The question was asked to me aparently somone bought the contents of a machine shop and all of the machines are 3 phase running on single phase power. I did find a RPC that could be built using 2 3 phase motors basicily you hook L1 and L2 to the 240 on both motors and L3 on the motors together and when running the motors act like a generator feeding each other the 3rd phase. I don't know how well it would work in the real world but apperently it is working at this establishment.

electrifried

I have done what you are talking about. I used a 10hp 3450rpm motor as the "converter". When energized You had to also imediatly pull a rope wound around a pulley to establish the rotation. then you could run up to 5hp of three phase motors. the nameplate HP value of the downstream motors was reduced considerably as was the torque value.

It worked to run a lathe in a buddys basement. Then a mill. He could use the tools just not at full output.

carl48

basically that is what a roto phase inverter is ,it has the extra winding built in the motor . the equipment will work at full rated power but the 30%loss in the single to three phase conversion might be a consideration. if you have a lathe or mill that is used occasionally it is not to bad. if you only have one a vfd is the way to go, this gives you any speed you want

carl48

basically that is what a roto phase inverter is ,it has the extra winding built in the motor . the equipment will work at full rated power but the 30%loss in the single to three phase conversion might be a consideration. if you have a lathe or mill that is used occasionally it is not to bad. if you only have one a vfd is the way to go, this gives you any speed you want

carl48

a roto phase inverter is a motor with the extra winding to produce the three phase it has about 20% loss but the tool has full power , if you only have one lathe or mill a vfd is the way to go it will give you completly variable speed.