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

"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

Greg Postma wrote:

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.

Almost. You can change the rpm of a three phase AC induction motor, but not a
single phase one.

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?

Yes, you can run them single phase input - three phase output.

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.

You can certainly use e.g. a 3hp VFD to run a 1hp motor, don't know if it would
be wise to use a 25hp VFD to run a 1hp motor. Can't go the other way, of course.

GWE

Greg Postma wrote:

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.
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Greg Postma wrote:

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?

Well unless your manual mentions that single phasing is a-ok w.o
derating, I'm thinking that you might want to derate it by 1.7 or so.
Just incase the full wave rectifier is sized for 3 ph.

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.

To some degree on most there are parameters you can set to protect
motor and drive. I'd stay away from more than a 2 or 3x mismatch where
the load is the small guy in circuit. JMHO.

Wes S
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Reply to:
Whiskey Echo Sierra Sierra AT Alpha Charlie Echo Golf Romeo Oscar Paul dot Charlie Charlie
Lycos address is a spam trap.

According to Greg Postma :

[ ... ]

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.

I'm using a 30A (7.5 HP max when running from single phase --
limited by the 30A circuit breaker) to run a 1HP motor on my Nichols
horizontal milling machine. They have no trouble running motors smaller
than their rating, unlike a static converter, which must be fairly
closely matched to the motor's HP rating so the start capacitor is
properly sized.

Enjoy,
DoN.

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