Is there any way to use a VFD to control the speed of a single (1)
phase motor?

thanks,
joyful

wrote:

Is there any way to use a VFD to control the speed of a single (1)
phase motor?

thanks,
joyful

I can't answer about what's actually done in practice, but in theory,
yes you could. There are a number of difficulties, even in theory, to
doing this, however.

The biggest problem would be starting, where you would need to drive
both the run coil and the start coil with the correct phasing (a single
phase motor with it's start coil is really a ******* two-phase motor).
The second biggest problem would be running smoothly at slow speeds
without overheating, which also involves driving the run and start coil
correctly. Because every model of motor has a different way of treating
start coils, making a universal VFD would be a big pain.

But a 3 phase motor has dead standard behavior, so a 3 phase VFD doesn't
need to be matched to a given model and brand of motor -- it can just go
by voltage and current rating (or voltage and horsepower).

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google? See http://cfaj.freeshell.org/google/

in a nutshell no.


wrote in message
ups.com...
Is there any way to use a VFD to control the speed of a single (1)
phase motor?

thanks,
joyful

Thanks Steve. That was a pretty small nut!

But isn't it possible to just use 1 phase of the VFD, disabling the
start winding/mechanism of the motor, or would this ruin the drive?
For and example, let's suppose I had a VFD rated at 3HP. If I used
only one phase could I drive a 1HP motor?

joyful

Thanks Tim for your reply. I really appreciate it. I had asked
another question that got on another group somehow, and that was: Does
anyone know where I can get info ON THE WEB that describes/shows
pictures., etc. of how to wind/rewind a 3 PH motor? One person sent me
to a small site that just gave electrical diagrams. I appreciate that
but, I need to know the actual congfiguraton that the wire/s are wound
in that stator.
The reason I'm asking is because I'm trying to avoid building
something that will do the job (namely: VFD) as I know I can't come
near to the quality/reliability of VFD products already out there.
It would also be helpful if I could see sketches of how the magnetic
fields are represented at different degrees, but I guess that would be
too much too ask. Reckon if I continue in this direction I'll just
have to sit down at the drawing board and figure it out myself. Any
other thoughts are welcome.
thanks,
joyful

wrote:

Thanks Tim for your reply. I really appreciate it. I had asked
another question that got on another group somehow, and that was: Does
anyone know where I can get info ON THE WEB that describes/shows
pictures., etc. of how to wind/rewind a 3 PH motor? One person sent me
to a small site that just gave electrical diagrams. I appreciate that
but, I need to know the actual congfiguraton that the wire/s are wound
in that stator.
The reason I'm asking is because I'm trying to avoid building
something that will do the job (namely: VFD) as I know I can't come
near to the quality/reliability of VFD products already out there.
It would also be helpful if I could see sketches of how the magnetic
fields are represented at different degrees, but I guess that would be
too much too ask. Reckon if I continue in this direction I'll just
have to sit down at the drawing board and figure it out myself. Any
other thoughts are welcome.
thanks,
joyful

I did a search on 'rewind motors how to' in altavista and got this:
http://www.easa.com/mo/TN-pdfs/TN35-1000.pdf.

If you want to rewind a motor into a 3-phase it'll have to have the
right number of stator slots, and they'll have to be even around the
circumference of the stator -- these are both things that you wouldn't
be able to count on from a single phase motor.

Frankly I think you could flip burgers and earn enough for a 3-phase 3HP
motor before you could figure out how to rewind one on your own. Unless
you want to know just to know, it's a losing proposition.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google? See http://cfaj.freeshell.org/google/

According to :
Thanks Steve. That was a pretty small nut!

But isn't it possible to just use 1 phase of the VFD, disabling the
start winding/mechanism of the motor, or would this ruin the drive?

It would not *start* the motor without the start winding, and
the proper frequency for that start winding and capacitor.

The motor needs that start winding to get started, since it does
not have any other windings to make use of the other phases from the
3-phase output of the VFD.

You might be able to set the VFD for 60 Hz, and spin the motor
by hand just before switching on the VFD -- but this would be quite
unsafe if you were trying to run any machine tool from the motor.

For and example, let's suppose I had a VFD rated at 3HP. If I used
only one phase could I drive a 1HP motor?

You could *drive* it -- at close to the normal speed -- if you
found some other way to get it started.

But you probably could not get *useful* power out of it over the
range of speeds that a real three-phase motor can do. At low speeds, it
is very likely to stall easily. At high speeds, the slip might be
excessive, and it might stall again.

Note that VFDs normally start a three phase motor at a very low
frequency (speed) and ramp it up to normal 60 Hz speed at a preset rate.
Even if you left the start winding and capacitor connected, the values
would be wrong until you got close to the standard 60 Hz output -- and
by that time, you might have fried the start capacitor, as they are not
made for long term operation.

Enjoy,
DoN.
--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

Hi Tim,

Thanks again. The old motor I have is a 3 phase I fished out of the
dump. And I agree that it's cheaper to buy one. But that is not why
I'm doing this. I just want to under stand how the thing actually
works. It's sorta like asking the climber why he wants to waste all
his time and energy climbing that mountain. No doubt he will answer:
"Because it's there". Well, it's good for my mind to have a puzzle to
keep it active. This just happens to be the latest one.
Thanks for the link. Don't know why google didn't offer this. Looks
like I've got some studying to do.
Have a good day,
joyful

Thanks Don. Looks like I better go find some other wheel to reinvent!

joyful