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Rotary Phase Converter

Introduction:
A rotary converter is a device used to create 3-phase power where only single-phase is available. They are frequently found in machine shops to power three-phase motors, however I built this particular converter to run my Spectra-Physics 168 Laser. One goal for this project was to build the converter as inexpensively as possible, without sacrificing safety or quality. I think I succeeded - by my count the converter cost less than $50!

Design:
The design of this converter is nearly identical to the one on LaserFX.com by Jake Wolfe. Instead of using a buck-boost transformer to drop the line voltage from 240 to 208, I used a 240 delta to 208Y three-phase transformer that came with the laser. It is a little bulky, but otherwise it does the job. I also added a 30HP contactor that I had laying around to allow for easy power-on and power-off of the system. The motor start capacitors, start relay, and voltage sensing relay are all mounted on the upper platform of the control box. The motor run capacitors are lined up underneath. For the idler motor on the original design I used a 30HP motor acquired at an auction for $5.00.


Phase Converter electronics		Phase converter, transformer, and 30HP motor

I quickly learned that 30HP is too much motor for a 30A breaker - it pops the breaker every time during startup. Thankfully I was able to borrow a 10HP motor from my friend Matt, who purchased it at the same auction for $5.00. I reduced the motor start capacitance by 1/2 and the run capacitance by 1/3 and it works great!

Modified phase converter with 10HP motor