Assuming adequate wire sizes for the starting load, you might try three
capacitors directly across the compressor leads. This could raise the power
factor and reduce current enough to permit starting.

Don Young
"Jeffrey M. Borning" wrote in message
...
I built a rotary phase converter using a 25HP motor. I am using 400uf Cp
and
20uF Cs with no Cpf. It just barley starts my brand new Ingersoll Rand
10HP
compressor with an empty tank but will pump it up to 175psi. It won't
start
the compressor when it cycles on at 135psi. The compressor turns slowly
and after about three revolutions it slows down and the overload trips. I
checked the unloader and it is working. I tried starting the compressor
motor without the belt on and it snaps right on, but apparently with the
inertia of the flywheel and pump, the motor draws too much current. It
pulls down V1-3 and V2-3 to about 140 volts before it kicks out the
overload.

Do I need a different or bigger idler motor or is my compressor motor just
that hard to start?

I thought that a 25HP idler would be big enough but evidently not. The
specs
on the idler a Linclon A.C. Motor, Lincguard Dripproof, Frame 284T,
1765
RPM, 25 HP, Insulation B, 230/460V, 62/31A, 40º Max Amb, 60 Hz, S.F. 1.15,
Time Rating Cont., NEMA Code G, NEMA Design B. I have heard that some
motors
do not make good phase converters, maybe this is one of them.

Any insight on this will be greatly appreciated. I bought the large
compressor specifically to do sandblasting and now I can't get it to work.

On a positive note, the phase converter seems to power up my 1HP
Bridgeport
OK. 8)

Jeff Borning