DIY Home Improvement Forum banner

1 - 7 of 7 Posts

·
Registered
Joined
·
3 Posts
Discussion Starter #1
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(What is a 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?



Final simplified design:



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.
 

·
Semi-Pro Electro-Geek
Joined
·
3,403 Posts
I'd probably just hack the starter motor's internal wiring to repurpose the centrifugal start switch as a cutout. Instead of transitioning from "start" to "run" at a certain RPM, the switch would transition from "start" to disconnected. This way you can keep power connected to the starter motor all the time but it will only be active when the unit is not spinning fast enough.
 

·
Registered
Joined
·
1,486 Posts
Why don’t you just use a solid state VFD to drive the 3 phase motor? Much simpler and they are quite inexpensive now.


Sent from my iPad using Tapatalk
 

·
Registered
Joined
·
1,486 Posts
Some people are self taught and they learn incorrectly but convince themselves otherwise.

Then when something “works” they declare it is ok.

The NEC wasn’t written to ensure things work, it is to ensure things are safe..


Sent from my iPhone using Tapatalk
 
1 - 7 of 7 Posts
Top