I own a laundromat and have 208 3ph machines. The control boards on the machines take 2 of the legs of the 3ph and run on 220vac which is then stepped down to various voltages on the board to make it work. The relays that control the motor have 220v coils and are triggered by smaller 24v relays on the board.

I'd like to make a power supply and test relay setup to test these boards at my home workshop. While my house does not have 3 phase service my knowledge of normal (not high leg delta) 3ph vs single phase is that if you grab 2 of the 3 legs on 3 phase it will product the same result as both legs on standard residential 240v single phase.

I'm pretty sure just running a 15A 2 pole breaker to my bench would work, but I don't want to go through the effort for something that I'm not going to use that often and doesn't even need that much power to work. What I'm looking to do is make a transformer that I can plug into a 110v outlet and get 220v split phase out. To make some of the elements work correctly the transformer would have to be able to output 110v when a single leg is grounded, and 220v (240v) when both of the "hot" legs are connected together.

The board itself and all of the controls wouldn't draw more than an amp of power. The only reason the board is using 3ph power is because of the giant motor that the washing machine uses, which won't be part of my test platform for the boards.

 

Why not run a 240v pair from the panel or off of a dryer outlet etc?
BTW, 2 phases off of a 3 phase supply IS single phase.
Or simply pick up a 120v/240v transformer?

 

My understanding is that 3 phase is 208/120 volts while home power single phase is 240/120 volts.

So something like an 120/88 volt transformer (or some combinations of transformers) could boost
the normal household 120 volts to 208 volts. It would be a good ide to have isolation from the AC
line in there somewhere (before the boost?) Or perhaps the right old tube power supply transformer
might do both the isolation and the boost.

As a separate issue, does the control board have a connection to the neutral?

I wonder if the control board is checking the phase rotation which would likely fail on a single supply.