Education needed,1 ph reverseing motor,,,,,,,,,,

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dicklaxt

Senior Member
I never gave this much thought ,I just accepted the fact the motor could be reversed.There is another post that has got the inquisitive juices flowing this morning,well actually yesterday and everytime I woke up last night.:)

I think I have a good understanding of how there is a phase shift between the start winding and the run winding due to start winding having smaller wire and less turns than the run winding blah,blah,blah.......Okay lets push the FWD Start button and everything is running fine,,,,now stop the motor,,,,,,,,"No problem yet".

Now lets REV the motor rotation,The switching arrangement in the control scheme reconnects(swaps) the conductors of the run winding end for end.I looked at several physical drawings of run windings and it appears the only difference now is that the wiring change over has also changed the ID of the run winding poles from N to S & S to N,if thats the case then the magnetic field of the run winding would also be reversed but at the same time opposing the start winding,,,,,,,"Having problems now".So if all of the above is fact and I'm not sure of that",is the newly directed magnetic field of the run winding overriding the magnetic field of the start winding as it should be trying to go the other way?,,,,,,,,,,"Now I am confused" The more I think about it the worse it gets. The run winding is wanting to rotate CCW and the start winding is wanting to rotate CW or vice versa.

Curious George would really like to know whats going on and how.

dick
 
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fmtjfw

Senior Member
It is not just the phase angle difference between the starting winding and the running winding that determines the direction the motor starts in, it is also the relationship of the currents in the windings and thus the magnetic fields generated by the windings.

Let's call the terminals for the running winding R1 & R2, for starting S1 & S2.

Let's call the supply red & black.

If R1, S1, and red are connected together (and R2, S2, and black) let's say the motor starts CW.
This happens because the starting winding "pulls" the rotor.

Now if you reversed one of the windings (in your case the running winding) you get R2, S1, and red connected (and R1, S2 and black)
Since it is AC the direction of the current is always changing and it does not govern the rotation of the motor. BUT the relationship between the currents in the two windings at any instant in time does govern the initial rotation. Note that relationship is now reversed between the starting and running windings. The motor now starts CCW. This happens because the starting winding "pushes" the rotor.

Without a connected starting winding you might be able to start the motor with a pull start like a lawn mower. If you pull it CW it starts CW and if you pull it CCW, it starts CCW. Note that this does not depend on whether you have wired it red R1 and black R2, or red R2 and black R1.

Hope this helps
 
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scott thompson

Senior Member
To Start a Single Phase Induction Motor (get the Squirrel-Cage Rotor to begin Rotating), one "Side" of the "Stationary" Magnetic Field must be "Reduced" - this is the Start Winding's sole purpose in life.

Connecting a Single Phase Induction Motor to an AC Source results in a "Balanced See-Saw" scenario, where the weights on either side of the See-Saw Board are equal, so the Board remains steady.

For the Motor, the Magnetic Field of a Single Phase Winding, as represented by a Phasor, is Stationary in Space, yet Alternating in Time.
This would be the sum of Two equal and oppositely revolving Phasors, which are constant in Magnitude (IIRC).

To get things moving, the Start (or Auxiliary) Winding reduces the Magnitude at one side of the Main (Run) Winding, which allows the Rotor to begin moving towards the reduced side - or more accurately, there is now less weight on one side of the See-Saw Board :lol: (AKA a Backward Field).

Direction of Rotation is determined by which side of the Run Winding has the reduced Magnitude, so changing the relative location where the Aux. Winding effects the Main Winding will effect the rotation direction.
This is accomplished by placing the Connection between the Main and Aux. Windings at a specific side.
To drive the Rotor in a Counter-Clockwise direction (standard "Foreward" rotation), the Aux. Winding would be connected, so as to reduce the "Right-Hand Side" of the Main Winding. The Aux. Winding would be on the Right-Hand Side of the Rotor, with the Main Winding on "Top" of the Rotor.
The Windings' connections would be the "Upper End" of the Aux. Winding and the "Left End" of the Main Winding connected together, and the "Lower End" of the Aux. Winding connected to the "Right End" of the Main Winding.

Reversing the connections, so the "Lower End" of the Aux. Winding is connected to the "Left End" of the Main Winding, places the Aux. Winding on the "Left-Hand Side" of the Rotor, which results in the Rotor starting in the Clockwise ("Reverse") Direction.

Make any sense??? :eek:

-- Scott (EE)
 

ronaldrc

Senior Member
Location
Tennessee
I never gave this much thought ,I just accepted the fact the motor could be reversed.There is another post that has got the inquisitive juices flowing this morning,well actually yesterday and everytime I woke up last night.:)

I think I have a good understanding of how there is a phase shift between the start winding and the run winding due to start winding having smaller wire and less turns than the run winding blah,blah,blah.......Okay lets push the FWD Start button and everything is running fine,,,,now stop the motor,,,,,,,,"No problem yet".

Now lets REV the motor rotation,The switching arrangement in the control scheme reconnects(swaps) the conductors of the run winding end for end.I looked at several physical drawings of run windings and it appears the only difference now is that the wiring change over has also changed the ID of the run winding poles from N to S & S to N,if thats the case then the magnetic field of the run winding would also be reversed but at the same time opposing the start winding,,,,,,,"Having problems now".So if all of the above is fact and I'm not sure of that",is the newly directed magnetic field of the run winding overriding the magnetic field of the start winding as it should be trying to go the other way?,,,,,,,,,,"Now I am confused" The more I think about it the worse it gets. The run winding is wanting to rotate CCW and the start winding is wanting to rotate CW or vice versa.

Curious George would really like to know whats going on and how.

dick



I understand your confusion.

I look at it like looking at a DC motor when you reverse it you reverse both windings.
So look at it like this instead of having as you said above N to S and S to N, now you will have S to N and N to S, the polarity has been reversed.
 

ronaldrc

Senior Member
Location
Tennessee
I have also noticed that no ones explains what really happens when we change the direction by reversing
the polarity ot the start winding.


I agree it is confusing if you change the North and south pole of the Run winding the induced armature North
and south poles will also be reversed.

It doesn't matter the motor will run in the direction it is forced to turn, and we know the start winding does that.

The graphic below should explain it.


Click here for a picture of how the motor reverses
 
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