I have this grinder that runs at 1725 rpm so it should have 4 poles.
Shouldn't I be able to tell which wires are for which poles by
checking the resistance? And If that works, can it be re-connected as
a two pole machine and still work at 115 volts? This is a capacitor
start/run machine with two identical windings and it uses two
capacitors to provide the phase shift. I don't know if the caps are
connected in parallel but it seems they should be as the motor only
runs in one direction. No starting windings in this motor, no
centrifigul switches.
Thanks,
Eric R Snow

Eric R Snow wrote:
I have this grinder that runs at 1725 rpm so it should have 4 poles.
Shouldn't I be able to tell which wires are for which poles by
checking the resistance? And If that works, can it be re-connected as
a two pole machine and still work at 115 volts? This is a capacitor
start/run machine with two identical windings and it uses two
capacitors to provide the phase shift. I don't know if the caps are
connected in parallel but it seems they should be as the motor only
runs in one direction. No starting windings in this motor, no
centrifigul switches.

Possibly. A few permanent split-phase capacitor motors are designed for
two- or three-speed operation. Is there any useful information on the
data plate?

Chris

The answer is yes and no. Yes, you could identify the poles as wound with
an ohmmeter if you could get to them - but no, you probably can't reconnect
it because the individual pole windings are not brought out to a convenient
point such as the junction box. In most cases to do this would be
tantamount to complete rewind - a truly daunting task for the uninitiated.

Bob Swinney
"Eric R Snow" wrote in message
...
I have this grinder that runs at 1725 rpm so it should have 4 poles.
Shouldn't I be able to tell which wires are for which poles by
checking the resistance? And If that works, can it be re-connected as
a two pole machine and still work at 115 volts? This is a capacitor
start/run machine with two identical windings and it uses two
capacitors to provide the phase shift. I don't know if the caps are
connected in parallel but it seems they should be as the motor only
runs in one direction. No starting windings in this motor, no
centrifigul switches.
Thanks,
Eric R Snow

Eric R Snow wrote:

I have this grinder that runs at 1725 rpm so it should have 4 poles.
Shouldn't I be able to tell which wires are for which poles by
checking the resistance? And If that works, can it be re-connected as
a two pole machine and still work at 115 volts? This is a capacitor
start/run machine with two identical windings and it uses two
capacitors to provide the phase shift. I don't know if the caps are
connected in parallel but it seems they should be as the motor only
runs in one direction. No starting windings in this motor, no
centrifigul switches.


What differentiates one pole from another is which way the wire is
wound around the coil. You would have to find the place where the
winding switches direction, and break the wire at that point and reconnect.
It would require a number of connection changes. As a 4-pole winding, the
polarity changes 4 times going around the full stator. As a 2-pole winding,
it would have to change only twice around the circle. Both the main winding
and the phase shifted winding would have to be rewired this way.
When done, you would end up with twice as many turns per pole as you
have now. That would make the stator iron pretty happy with the magnetic
situation, but as the rotor field would be moving twice as fast through
twice as many turns per pole, I'm not sure how that would work out.
(Something tells me it will all balance out, as the rotor field will
equilibrate
at 1/2 the strength, and you'd get half the torque at twice the speed.)

Jon

Robert Swinney wrote:
The answer is yes and no. Yes, you could identify the poles as wound with
an ohmmeter if you could get to them - but no, you probably can't reconnect
it because the individual pole windings are not brought out to a convenient
point such as the junction box. In most cases to do this would be
tantamount to complete rewind - a truly daunting task for the uninitiated.

This is true if the motor is designed as a single speed, four pole
machine, but I think Eric is referring to a machine which is designed to
run at two speeds. If he has a motor like this, it should be possible to
change the speed without even opening the case.

Chris

On Thu, 26 May 2005 22:19:11 +0000 (UTC), Christopher Tidy
wrote:

Eric R Snow wrote:
I have this grinder that runs at 1725 rpm so it should have 4 poles.
Shouldn't I be able to tell which wires are for which poles by
checking the resistance? And If that works, can it be re-connected as
a two pole machine and still work at 115 volts? This is a capacitor
start/run machine with two identical windings and it uses two
capacitors to provide the phase shift. I don't know if the caps are
connected in parallel but it seems they should be as the motor only
runs in one direction. No starting windings in this motor, no
centrifigul switches.

Possibly. A few permanent split-phase capacitor motors are designed for
two- or three-speed operation. Is there any useful information on the
data plate?

Chris
No. It's a Baldor motor. Two voltage capability. But nothing about
different speeds.
ERS

On Thu, 26 May 2005 17:46:01 -0500, Jon Elson
wrote:



Eric R Snow wrote:

I have this grinder that runs at 1725 rpm so it should have 4 poles.
Shouldn't I be able to tell which wires are for which poles by
checking the resistance? And If that works, can it be re-connected as
a two pole machine and still work at 115 volts? This is a capacitor
start/run machine with two identical windings and it uses two
capacitors to provide the phase shift. I don't know if the caps are
connected in parallel but it seems they should be as the motor only
runs in one direction. No starting windings in this motor, no
centrifigul switches.


What differentiates one pole from another is which way the wire is
wound around the coil. You would have to find the place where the
winding switches direction, and break the wire at that point and reconnect.
It would require a number of connection changes. As a 4-pole winding, the
polarity changes 4 times going around the full stator. As a 2-pole winding,
it would have to change only twice around the circle. Both the main winding
and the phase shifted winding would have to be rewired this way.
When done, you would end up with twice as many turns per pole as you
have now. That would make the stator iron pretty happy with the magnetic
situation, but as the rotor field would be moving twice as fast through
twice as many turns per pole, I'm not sure how that would work out.
(Something tells me it will all balance out, as the rotor field will
equilibrate
at 1/2 the strength, and you'd get half the torque at twice the speed.)

Jon
Jon-I didn't think about the torque drop. Of course it would have to
drop. Otherwise the motor would change from a 1/2 hp to 1 hp. Maybe I
should just leave it alone.
Eric

Eric R Snow wrote:
On Thu, 26 May 2005 17:46:01 -0500, Jon Elson
wrote:



Eric R Snow wrote:


I have this grinder that runs at 1725 rpm so it should have 4 poles.
Shouldn't I be able to tell which wires are for which poles by
checking the resistance? And If that works, can it be re-connected as
a two pole machine and still work at 115 volts? This is a capacitor
start/run machine with two identical windings and it uses two
capacitors to provide the phase shift. I don't know if the caps are
connected in parallel but it seems they should be as the motor only
runs in one direction. No starting windings in this motor, no
centrifigul switches.



What differentiates one pole from another is which way the wire is
wound around the coil. You would have to find the place where the
winding switches direction, and break the wire at that point and reconnect.
It would require a number of connection changes. As a 4-pole winding, the
polarity changes 4 times going around the full stator. As a 2-pole winding,
it would have to change only twice around the circle. Both the main winding
and the phase shifted winding would have to be rewired this way.
When done, you would end up with twice as many turns per pole as you
have now. That would make the stator iron pretty happy with the magnetic
situation, but as the rotor field would be moving twice as fast through
twice as many turns per pole, I'm not sure how that would work out.
(Something tells me it will all balance out, as the rotor field will
equilibrate
at 1/2 the strength, and you'd get half the torque at twice the speed.)

Jon

Jon-I didn't think about the torque drop. Of course it would have to
drop. Otherwise the motor would change from a 1/2 hp to 1 hp. Maybe I
should just leave it alone.
Eric


I'm pretty sure you get full torque at (about) double speed. Same stator
windings = same flux in the same rotor. The rotor is moving through half
the number of lines of flux twice as fast. Based on the thought of a
motor being a transformer with a rotating secondary, the rotor currents
should be twice nominal with no load, and the rotor voltage twice
nominal at full (double the nameplate HP) load. If that last part is
backwards, someone please correct me.

John

Eric, you can't change the speed of that grinder. Sorry. - GWE

On Fri, 27 May 2005 12:28:37 -0400, JohnM wrote:

Eric R Snow wrote:
On Thu, 26 May 2005 17:46:01 -0500, Jon Elson
wrote:



Eric R Snow wrote:


I have this grinder that runs at 1725 rpm so it should have 4 poles.
Shouldn't I be able to tell which wires are for which poles by
checking the resistance? And If that works, can it be re-connected as
a two pole machine and still work at 115 volts? This is a capacitor
start/run machine with two identical windings and it uses two
capacitors to provide the phase shift. I don't know if the caps are
connected in parallel but it seems they should be as the motor only
runs in one direction. No starting windings in this motor, no
centrifigul switches.



What differentiates one pole from another is which way the wire is
wound around the coil. You would have to find the place where the
winding switches direction, and break the wire at that point and reconnect.
It would require a number of connection changes. As a 4-pole winding, the
polarity changes 4 times going around the full stator. As a 2-pole winding,
it would have to change only twice around the circle. Both the main winding
and the phase shifted winding would have to be rewired this way.
When done, you would end up with twice as many turns per pole as you
have now. That would make the stator iron pretty happy with the magnetic
situation, but as the rotor field would be moving twice as fast through
twice as many turns per pole, I'm not sure how that would work out.
(Something tells me it will all balance out, as the rotor field will
equilibrate
at 1/2 the strength, and you'd get half the torque at twice the speed.)

Jon

Jon-I didn't think about the torque drop. Of course it would have to
drop. Otherwise the motor would change from a 1/2 hp to 1 hp. Maybe I
should just leave it alone.
Eric


I'm pretty sure you get full torque at (about) double speed. Same stator
windings = same flux in the same rotor. The rotor is moving through half
the number of lines of flux twice as fast. Based on the thought of a
motor being a transformer with a rotating secondary, the rotor currents
should be twice nominal with no load, and the rotor voltage twice
nominal at full (double the nameplate HP) load. If that last part is
backwards, someone please correct me.

John


Because of the way the windings are distributed in the stator
slots (multiple coils spanning a 90 deg segment) there is no way of
reconnecting the coils to produce an efficient new distribution
spanning the 180 deg segment needed for a 2 pole winding.

A complete rewind is required using fewer turns of thicker wire
and, if operated at the same flux density will produce the same
torque at twice the speed - i.e. twice the HP. Various second order
effects chip away at this power increase but an 80% power increase is
entirely possible.

Jim

Eric R Snow wrote:
On Thu, 26 May 2005 22:19:11 +0000 (UTC), Christopher Tidy
wrote:


Eric R Snow wrote:

I have this grinder that runs at 1725 rpm so it should have 4 poles.
Shouldn't I be able to tell which wires are for which poles by
checking the resistance? And If that works, can it be re-connected as
a two pole machine and still work at 115 volts? This is a capacitor
start/run machine with two identical windings and it uses two
capacitors to provide the phase shift. I don't know if the caps are
connected in parallel but it seems they should be as the motor only
runs in one direction. No starting windings in this motor, no
centrifigul switches.

Possibly. A few permanent split-phase capacitor motors are designed for
two- or three-speed operation. Is there any useful information on the
data plate?

Chris

No. It's a Baldor motor. Two voltage capability. But nothing about
different speeds.
ERS

The dual voltage capability will be the reason for the two identical
main windings. They will be connected in parallel for 115 V operation or
in series for 230 V operation. They aren't intended for speed control. I
think the only way you can vary the speed of this motor is to change the
supply frequency.

Hope this helps,

Chris

In article ,
Christopher Tidy wrote:


Eric R Snow wrote:

[ ... ]

No. It's a Baldor motor. Two voltage capability. But nothing about
different speeds.
ERS

The dual voltage capability will be the reason for the two identical
main windings. They will be connected in parallel for 115 V operation or
in series for 230 V operation. They aren't intended for speed control. I
think the only way you can vary the speed of this motor is to change the
supply frequency.

And not very much, with a single phase cap start motor -- unless
you are willing to switch the start capacitor value each time you change
the frequency.

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 ---