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wrote:
You might want to consider that a induction motor that is driven acts
as a induction generator. Jim Pentagrid has posted some very accurate
information about induction generators. To summarize, they are very
load sensitive if they are used as a stand alone generator. But if
they are connected to the power grid, they work very well.

So you can make a motor generator using a single phase motor driving a
three phase motor which has one phase connected to the same single
phase that drives the single phase motor. Nota Bene In order to
actually be driving the three phase motor, you have to drive it faster
than the rpm that it would run at when running on single phase as a
idler. The way to do this is with a belt drive. One pulley should be
a variable pulley. So one can measure the current drawn by the single
phase motor and adjust the pulley so the single phase motor draws its
nameplate current or somewhat less.

This is the way to make a phase converter for driving something as a
surface grinder that is sensitive to variations in torque.

I made one like this some twenty years ago to run a centerless sander.
Worked slick. The single phase motor worked as a pony motor to start
the three phase motor and then drove the three phase motor to produce a
better three phase than most rotary three phase converters.

Dan,

This is a really interesting suggestion. What size motors did you use? I
can get a 2.5 hp three phase motor free, and a 3/4 hp single phase motor
for little money. How do you think this would work? From what I've read
phase convertors are pretty forgiving about the size of motors used.

Many thanks,

Chris