Rotary phase converter for conversion of single phase power to run 3 phase machines

Before you start, know what precautions to take when working with electricity and machinery that can start automatically or call an electrician to check your work and for final connection and testing.

  I've built a bunch of these, and they are very reliable, but for very frequent starting it would be an improvement to use a relay on the start button as after a few hundred cycles the contacts in the start switch may get burned up.  You can also keep an extra contact block for the switch just in case.  My converter is around 10 years old and I haven't had to replace the switch yet even though I only run it intermittently and start it multiple times a day.  For me these units generally do not perform well with air compressors (or machinery with very high starting loads) or welders.  Many 3 phase mig welders can be operated single phase with a haas-kamp conversion (Google it).  If you need higher than your power company voltage put the transformer between your breaker box and the converter, wire the idler and size the contactor and overloads for the appropriate load at the higher voltage.
   You can use a surplus 3 phase motor, RPM does not matter, and you can mount a buffing wheel or make similar use of that spnning idler motor shaft rather than removing or covering it..  Capacitor values will require some trial and error to get all 3 phase legs within about 7% of each other, or under 5% for CNC machines.  Run the power company lines to the controls of your target machine, and use the generated leg to run the spindle and other motor loads.  The starting load of your machine may cause a brief sag in the generated leg of the converter,  a symptom of which is when your target machine's motor starter contactor "stutters" and the machine will not start or the converter shuts down.  This stutter is the phase protection on the contactor in the target machine reacting as if you have lost one leg of power so it disconnects, in the brief moment the capacitors in your converter catch up before it has a chance to completely disengage and repeats.  Not good for the starter contacts.  In a pinch if you get this stutter try to manually actuate the machine contactor by pressing the movable contact with a non-conductive non-metallic object; your machine should start and stay running.  If the stutter occurs even with the power company legs to the controls you may not have large enough wiring, voltage too low, or other issues.  
   Get your capacitors from ebay or surplus center, the motor from a salvage yard, and the contactor, buttons and terminal blocks from or Automation Direct.  Its not worth building one of these unless you use a 5hp motor or larger as variable frequency drives in the 3hp and under range with single phase input and 3 phase output are cheap AND give you variable speed capability, which these do not. This design uses full voltage to the controls; if you wish to have your buttons in a separate box, it would be best to use a 24v control circuit and a contactor with 24v coil so you don't have line voltage in the conduit to your control box.


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