"Greg Postma" wrote in message
...
I'm trying to understand the application of VFDs in industry. I understand
the basics,ie; by changing the frequency of AC current, you can change the
rpm of an AC induction motor. This is a good thingG. I know that things
like fans, pumps and conveyors are great applications for VFDs because you
can change the speed of the motor to match the load. I also think that
VFDs will work with machine tools because the VDF allows the spindles to
be run at an infinite number of speeds, negating the need for some belts,
pulleys or transmissions.

Looking at VDFs available on Ebay, it appears that the input on some of
them are single phase and some are 3 phase, but all VDFs have a 3 phase
output.It appears to me that one could use (a properly rated) VDF instead
of a phase converter to convert 230v single phase to 3phase at 230v or
460v. Am I correct?

The VDFs listed on Ebay are for fractional horsepower all the way up to 50
hp and higher. Does the VDF rating have to match the HP rating of the
motor, or could one use a VDF rated at 3 hp to drive a smaller motor like
a 1 hp motor? I know that it would not be a good thing to use a VDF rated
at 3hp to run a 25 hp motor.

Greg

I asked an electrical engineer at work and he says that yes, this will work,
but you should size the VFD by amperage, not by HP (though the amperage/hp
sizing will be close to the same). You are also correct in your assumption
that you can use a larger VFD to run a smaller motor, but you shouldn't go
the other way around.

Relz