does anybody know how to wire up 3 phase to single phase without using a converter?

Question

i have 7hp. 3 phase air compressor and i want to hook it up to single phase 220 with this same motor without buying a converter i was told it was possible, does anybody know how

Answer 1

Occasionally the advantages of three-phase motors make it worthwhile to convert single-phase power to three phase. Small customers, such as residential or farm properties may not have access to a three-phase supply, or may not want to pay for the extra cost of a three-phase service, but may still wish to use three-phase equipment. Such converters may also allow the frequency to be varied allowing speed control. Some locomotives are moving to multi-phase motors driven by such systems even though the incoming supply to a locomotive is nearly always either DC or single phase AC.

Because single-phase power is interrupted at each moment that the voltage crosses zero but three-phase delivers power continuously, any such converter must have a way to store energy for the necessary fraction of a second.

One method for using three-phase equipment on a single-phase supply is with a rotary phase converter, essentially a three-phase motor with special starting arrangements and power factor correction that produces balanced three-phase power. When properly designed these rotary converters can allow satisfactory operation of three-phase equipment such as machine tools on a single phase supply. In such a device, the energy storage is performed by the mechanical inertia (flywheel effect) of the rotating components.

A second method that was popular in the 1940's and 50's was a method that was called the transformer method. In that time period capacitors were more expensive relative to transformers. So an autotransformer was used to apply more power through fewer capacitors. This method performs well and does have supporters, even today. The usage of the name transformer method separated it from another common method, the static converter, as both methods have no moving parts, which separates them from the rotary converters.

Another method often attempted is with a device referred to as a static phase converter. This method of running three phase equipment is commonly attempted with motor loads though it only supplies ⅔ power and can cause the motor loads to run hot and in some cases overheat. This method will not work when any circuitry is involved such as cnc devices, or in induction and rectifier type loads.

Some devices are made which create an imitation three-phase from three-wire single phase supplies. This is done by creating a third "subphase" between the two live conductors, resulting in a phase separation of 180° − 90° = 90°. Many three-phase devices will run on this configuration, but at lower efficiency.

Answer 2

How To Wire 3 Phase Motor

Answer 3

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You cannot rewire the motor but you can convert single-phase to 3-phase power using a rotary converter or an electronic inverter. A third type, the static converter, is simpler but allows you to operate your equipment at only 2/3 its rated power, so it is generally not recommended. This may be what was referred to as a "transformer", but it's not that simple - a transformer alone cannot generate 3-phase power from a single phase.

Answer 4

I don't think you can get there from here.... not without a convertor. You could use the capacitor method as suggested but you would in the end damage the motor as their wouldn't be enough torque available for the motor to pump the compressor up to it's off point. It might get there once twice or even a hundred times, but eventualy you will burn out the motor. If you reduce the upper limit so that the compressor isn't trying to get up to the normal upper pressure it might work though.

Answer 5

My advice is that you buy the convertor. The pseudo three phase method is inefficient as pointed out by Crimsonblade. If you use that method, it means you are getting a lot less from the air compressor OR you end up paying more for the power consumed. Cheerios!

Answer 6

Aside from the complications mentioned in the various methods, you have to look at the current draw - 7 horsepower drawing on single phase to going to suck huge amps no matter how you convert it. Even more when the motor starts against load.

Answer 7

It is possible the other way round i.e. single phase from 3-phase. In three phase you need 3 hot wires and one ground. In single phase you have one hot wire and one ground!