123 Phase Converter

Jan 2001 ~ by Griz (aka Steve Stovner) ~
I needed 3 phase power for some motors I had and for future shop equipment. In 2001 VFD's were still a thing of the future. Static units were very expensive for anything over 1 HP and produced very poor power. The only 10 HP rotary phase converter I found was far more than what I could or would pay. So, I built my own. Research yielded basic directions on how to start 3 phase motor on single phase and how to use capacitors to balance the phase angle and voltage of the 3 legs.

For those who don't know how a rotary phase converter works: A 3 phase motor will not start by powering 2 legs with single phase. But once turning the third leg becomes a generator and produces its own power which both feeds the motor and can be tapped for external use.

Overview of my design:

• 10HP 240vac 3 phase motor, 3600 RPM.
• Pushing momentary start button energizes latching Start-Relay.
  • 240vac single phase is applied to legs 1 & 2 of motor.
  • Start-Capacitor is connected between leg 2 & leg 3 of motor. (provides enough phase shifted power to leg 3 for the motor to start turning).
• The faster the motor turns the more voltage is produced on leg 3 - further increasing rpm.
• When voltage of leg 3 reaches ? volts (indicating 95% rpm), Run-Relay energizes.
  • Start-Relay is deenergized.
  • Start-Capacitor is removed.
  • Run-Capacitors are already connected (to balance phases and voltages).
  • 20 second timer starts (to allow time for system to stabilize).
• After 20 sec. timeout, 3 phase power is connected to output of converter.
• Pushing momentary stop button deenergizes Run-Relay:
  • Disconnecting output power.
  • Disconnecting input power to motor.

2024 ~ by Griz (aka Steve Stovner) ~
23 years later and It's still a very valuable, very reliable addition to my shop. I use it all the time for Mill, Lathe and other 3 phase stuff.

When I built it my grandson Robby was 3 years old. Since he was in my shop quite often, I assumed he would discover the "pig" and be thrilled (or at least intrigued), but alas, he was 15 years old when he finally noticed it.

Never count of kids to do or be what you expect.
Love them whatever they do or become.
~ Griz ~