# DIY Rotary Phase Converter with starter motor, cutout relay in parallel with load?

I am working on a DIY Rotary Phase converter with pony motor. This will use single phase 240v and run capacitors to feed 2 legs of a 3 phase motor, which will generate the 3rd leg.

It uses a 1/2 HP 120v motor (pony motor, starter motor) to start a 5 HP 3 phase motor. I would like auto-start and cutout, so the idler and starter are never energized separately and the starter cuts out after the idler spins up.

The approximate design is below. A 120v switch turns on the starter motor and a 2 pole relay to power L1 and L2 of the idler. The idler has run capacitors between L1-L3 and L2-L3. When the idler starts, L3 will energize the cutout relay (240v NC), which turns off the starter motor. L1, L2, and L3 would be used to drive a 3 phase load.

I used ground symbol for neutral in the schematic.

My primary concern is with the cutout relay wired in parallel with the load on L3. Will this cause problems? If so is there an easy modification I can make to the circuit? Will the cut out relay energize prematurely due to the run capacitors?

simulate this circuit – Schematic created using CircuitLab

Information regarding rotary phase converters: http://www.metalwebnews.com/howto/ph-conv/ph-conv.html http://www.paragoncode.com/shop/rotary_converter/

Final simplified design:

simulate this circuit

The circuit diagram tool doesn't have an option for aux contactors or 3 pole relays, so RLY AUX indicates a 3rd pole or an AUX connection on the contactor

• Why are there lamps in series with the start motor and the cutout relay? Are you using a lamp to drop the voltage because the cutout relay has a 120 volt coil? Is the voltage across L1 and L2 240 volts from two 120 volt hot lines? Please revise the question to make it more clear. – Charles Cowie Jan 15 '17 at 19:44
• If you are trying to implement a scheme that you found on the internet, a link to the original description might help. – Charles Cowie Jan 15 '17 at 20:07
• Lamps were superfluous. L1-L2 is 240v. The cutout relay would be a 240v NC relay. The phase generation part isn't really where I have questions, I'm trying to see if powering a relay off of 1 leg of the 3 phase side will cause problems, or energize so fast that the starter won't spin up. – user15741 Jan 15 '17 at 20:48