In article , Richard Ferguson says...

I have been hearing about VFDs and other types of solid state controls.
The Phase Inverter seems not to offer variable speed, but lots of
features. I presume similar units are available with variable speed.

However, it would seem to me that you would need a specific variable
speed drive for each tool, that you would not want to walk to the corner
to adjust the speed. That could get pricy.

In principle one *could* run low voltage control lines to each
machine, and switch them so whatever machine you are running
has the active lines. Sounds like a major nosebleed to me
though.

To me the most practical (cheapest) thing would be to have one convertor
for the whole shop, asuming that you might eventually have multiple
devices with 3-phase motors.

This is what I do, with a simple idler motor setup:

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

http://www.metalworking.com/DropBox/_2000_retired_files/conv.txt

(the text should be annotated to include the *real* current
draw when idling, which is about 200 watts)

1. Static [] converter, simple, only gives 2/3 power, probably costs
around $100 for under 5 hp. Probably could be shared by several machines.

The static converters are special sized for each machine, you
can't run a large machine with a small converter, or a small
machine from a large static converter.

2. Rotary converter - full power, could be cheap if you use an old 3
phase motor to make your own, or more expensive if you buy one new.
Could be noisy. Often shared by multiple machines.

Cost for mine: free, except for the wire and wiring devices.
It's so quiet I can forget that it's running and accidentally
leave it on.

3. Phase inverter - solid state, I think that you said $700. I think
that you said that they could be shared, but you lose some of the
sophisticated features in that case.

4. Variable Frequency Drive - the top of the line solution, provides
electronic variable speed control. I would assume the top price. I
would guess that with some machines, you might want to run part of the
machine with the VFD, while running other parts with straight 3-phase
power, like the controls. It would seem unlikely that one would share
the VFD, but maybe some people do.

I haven't seen any phase inverters that don't also incorporate
variable speed options. At least for the smaller ones I've
seen. YMMV.

What is the price range here?

Zero to hundreds of dollars, depending on size of load.

Which of these solutions can be shared
between multiple devices?

All of them to some degree or another. Easiest seems to
be the single point idler motor setup, for this factor.

Am I wrong about what I said above? I am
trying to make sure that I understand.

You pretty much understand the issues.

Jim

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