How to Make Your Own 3-Phase Converter

A rotary 3-phase convertor can be made from a 3-phase alternating current (AC) motor. This type of motor does not start with single-phase power, but it can be connected to single-phase AC power and manually spun with a rope to start it. After it is started, the motor spins on its own. While spinning, it produces 3-phase AC power for powering industrial tools that need this type of power source. Assembly of a rotary 3-phase convertor is something that can be completed by someone with electrical knowledge. In addition, at least some of the parts are salvageable to make the converter economical.

Many industrial tools require 3-phase AC power.

Step 1

Connect a 30-amp circuit breaker to your 230 VAC single-phase power source.  If your motor draws less or more amperage, install a breaker of the appropriate size.

Connect the 10-gauge copper wiring to that breaker to provide electrical leads going to your 3-phase motor. 

Step 2

Connect the two hot leads of the 230-volt power source to the T1 and T3 terminals of the motor.  Use the 10-gauge wiring.

Connect the ground wire to a terminal on the motor casing.  Install the 10-, 12- or 14-gauge wiring in three separate leads from T1, T2 and T3 on the motor and connect to the overload relay.

The choice of wiring size for the output depends on the current draw of the equipment you are using. 

Step 3

Connect one of the capacitors between the T1 and T3 wires that exit from the overload relay.  Connect the other capacitor between the T2 and T3 wires.

Continue the T1, T2 and T3 wiring to a power outlet for connecting the machinery. 

Things You Will Need

  • 3-Phase AC motor, 5-horsepower (HP)
  • 30-amp circuit breaker
  • Overload relay, 7-10 amps, 3-phase
  • Copper wiring, 10-gauge, 3-wire
  • Copper wiring, 10-to-14 gauge, 3-wire
  • 2 Oil-filled capacitors, 60-80 microfarads
  • Lawn mower starter rope


  • Motors with lower speed ratings can be easier to start.
  • Buy a high quality 3-phase motor for long service life.
  • Run capacitors are sized based on the formula of 12-16 microfarads per HP.
  • The run capacitors are not required, but they allow the convertor to produce 20-percent more power because there is less current in one of the lines. They also balance the voltage and current draw on the three legs, making for an even load on the windings of the powered device.
  • Refer to tables of wire sizes and amperage ratings to choose the correct size of wiring for the current draw of your 3-phase equipment.


  • If you do not understand electrical wiring, hire a licensed electrician to install the breaker and make the wiring connections.
  • Follow the electrical codes of your locality.
  • Disconnect the power before starting electrical wiring.

About the Author

As a scientist, Randy McLaughlin has been a professional technical writer since 1980. He has a Master of Science from Texas A&M University and a Ph.D. in plant pathology from the University of Wisconsin. McLaughlin covers diverse topics, including Costa Rica, technical guides, alternative healing and spiritual development.

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