"DoN. Nichols" writes:

A VFD is a big magic solid state box that delivers AC of from {say} 10Hz
to 100Hz. It USUALLY will be one able to deliver 3 phase power. [But
there may well be smaller single phase ones, so cabbage emperor...]

There are smaller ones designed to *run* only from single phase,
and power a 1/8 HP motor (I have one -- about the volume of a brick and
a lot lighter).

But not for driving normal single phase motors at variable
speeds.


Don, I was specifically trying to keep it simple and on-topic. The OP's
concern is getting a VFD {or other solution} for his case. I just didn't
want him buying some weird eBay VFD that WAS single phase...because
he assumed "VFD == 3 phase"

How it does that.... Well think of it as an audio oscillator and a
BIG amplifier for the speakers err motor.

Except that it is normally done by PWM (Pulse Width Modulation)

Again....TMI

It's almost a waste to buy one just for a single speed task, but a
friend did to drive an air compressor.

Air compressors can draw a *lot* of power, and running one from a VFD
(if you run it a lot) will probably cover the cost of the VFD in power
bill savings over two or three years. They are close to 100% efficient
because of the switching mode output, while a RPC is rather inefficient.

This runs a big hammer -- I suspect it's occasional use only. He had
3 phase very nearby, but the utility wanted lot$ to bring it in.


A rotary converter is a semi-kludgey way of getting 3 phase from a single
.....

Actually -- a *larger* idler motor than the load motor (1.5x or
2x) will probably provide all the torque you need -- especially if you
take time to balance the converter by adding capacitors between the
generated phase and the other two legs to produce approximately equal
current in each leg.

And how many ram types would do that?

I will admit I'd not considered the instant reverse aspect. That might be
reason for the rotary converter approach.
--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433