In article , FLowen says...

gotten the full range of recommendations. Some say a static electronic
converter at $150 is plenty sufficient; others say I should go with a
$500+ rotary converter with a 5HP capacity (I don't plan to add any
other 3 phase equipment); and one fellow suggested making a "pony
motor" from a used 2-5 HP 3 phase motor, wired with the 2 legs of
single phase input power to 2 of the 3 motor terminals, and then the 3
terminals to the machine, equipping the pony motor with a hand start
pull cord, ever hear of that? I'd like to hear the thoughts of you
experienced folks.

The pony motor is a single phase motor that takes the place
of a (dangerous IMO) rope pull.

The larger three phase motor that is being started this way
is called the 'coverter' motor or more commonly the 'idler'
motor.

You can see my setup with a 5hp idler motor and a 1/8 hp
pony motor to spin it up before I turn on the power to
excite the idler:

http://www.metalworking.com/DropBox/_2000_retired_files/Conv.jpg

The entire thing was built for free, and runs all my machines, none
of which are more than 1 hp apeice. Because the motor is large
in comparison to the load motors there is no fancy tuning required.

The pony motor spins the idler up to speed, I turn on a fused
knife switch to excite two of the three wires in the idler motor,
and then it locks in to the line frequency and runs on its own.

I lift up the hinged platform that the pony motor sits on and
the belt flies off. The thing is so quiet when running I've
been known to nearly forget and leave it running. It consumes
about 200 watts when it is not powering the load motor.

Jim

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