Hi Ruuf,
My converter was built in 1984 using paper plans. Thought I saved them, and probably did inside the box on the converter that is presently in storage about 20 miles away.
Here are a couple of resources:
SINGLE to 3 PHASE CONVERTER
The author, Jim Hanrahan, includes a good description and schematics. Figure 1 shows two run capacitors and a start capacitor. While his design is self-starting, the start capacitor does not automatically disconnect when the converter ("idler motor") gets up to speed. The user has to hold the start button in for that time (it is about 1 to 2 seconds).
One way around that is to use a potential relay, such as are used in HVAC and other installations, on the generated leg of the 3-phase. When the idler is up to correct speed, the voltage in that leg increases, and the potential relay automatically removes the start capacitor from the circuit. My converter works like that. You just turn one switch on, you hear the potential relay click, and you have 3-phase. I would strongly recommend going with the automated disconnect for the start capacitor.
Here is a link to a circuit that uses a potential relay:
Phase Converters
We don't know where you are located. Potential relays may be hard to find at consumer outlets. Check with a industrial outlet (such as Grainger) or HVAC supplier.
For my converter, I used a 5HP Baldor 3-phase motor. It was cheap, because the seller got it by mistake. I had a 8"x8" enclosure mounted to the side with a 3-ph socket and on-off switch. The capacitors and relay fit nicely inside. A 3-hp lathe and mill worked fine off of it. I have heard that while the newer motors work as rotary converters, the older, heavy-iron motors work better.
John