You know the 2 wires you connect to get 220 single phase power? Call those
line 1 and line 2 (L1 and L2). Connect those to any two of the 3 legs of
the 3hp 3-phase motor through a 30A single phase disconnect (about $10)
using Buss slow-blow fuses in the disconnect box. Connect your load motor
(the 3/4hp one) to L1, L2 and L3 via another cheap disconnect box. Put
a small (10x10x6") electrical box somewhere close and run L1, L2 and L3
to that box. Put an oil-filled motor run capacitor rated for 220VAC between
L1 and L3, and another between L2 and L3. These will be sized big enough
to quiet the buzzing down and small enough so it doesn't start back up
again. If you want to start it using a rope then you're done, otherwise
you need to add some electrolytic motor start capacitors between L1 and L3
in some kind of circuit that will take the capacitors out after the motor
has started. This can be done using a heavy duty pushbutton switch, or
by using a potential relay from Grainger to automatically take out the
start caps.

There are real good schematics available online, but I don't have the
link handy. Google will tell you a lot.

Grant Erwin

Pdelpriore wrote:

I have a 220 v 3 phase, 3/4 horsepower motor and want to run it from a 220 v
single phase source.
I have a 220 v 3 phase, 3 horsepower motor that I would like to use as a
rotary phase converter. I have a 25, 35, 40 and 40 uf capacitors. I need help
on how to wire these.

Thank you.

Paul