Unless you are rasonably well versed with electricity, I wouldn't recommend you or anyone else to try to build you own rotary phase converter....that being said,
The reason many home made converters seem to have less than a stellar performance is that they usually apply incoming power to the rotary converter with the third leg through a run capacitor (or capacitors in parallel) without first using a "pony" motor and a time delay relay to get the 3 phase motor "up to speed" first.
Sure, it will start on single phase by paralleling one of the legs through the capacitor to the third winding, but it will never attain full speed, consequently not optimum output either. However.... using a pony motor with the same rpm rating of the 3 phase motor you are using and connect them together with a lovejoy coupling or even same size sheaves and a belt you will first get the driven motor to full speed then the time delay relay will drop power off of the pony and simultaneously apply 220v single phase with the third leg going through the capacitor AFTER full rpm is achieved. It still will not supply the rated power, but it will perform remarkably better.
Typically one 20 mfd oil filled run capacitor will suffice on most small 1, 2, 3 and even a 5 hp three phase motor. It's not going to be perfect, and it is considered a pretty dirty three phase power, it will work for a home work shop. With an oscilloscope and a pile of additional capacitors, in theory, you should be able to keep adding capacitance in parallel until you get very near to a 120 degree phase shift. A three phase motor has three identical windings and with correct three phase power applied, has 120 degrees phase shift between the three windings. That is the reason they are referred to as a motor with "high starting torque".
Without the capacitor, you will "single phase" the motor and it will literally smoke in minutes....all the capacitor is doing is creating a little offset in the third leg (ergo: phase shift) to allow rotation to initiate. Not being a perfect 120 degree phase shift is what causes it to be underpowered. Nature of the beast.
That all being said, this description is totally incomplete and not intended to suggest that you should try it at all !!! But it DOES work for me in the way it is described. As a matter of fact you should be able to easily run a total horsepower higher than that of the motor you are using for the rotary converter.
Not for the faint of heart, and NOT RECOMMENDED for a rookie with little or no electrical background.....BE SAFE !!!!! ...and enter John T's normal disclaimer here: "____________________"
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