chris kennedy
Senior Member
- Location
- Miami Fla.
- Occupation
- 60 yr old tool twisting electrician
How does it know which way to start turning?
1? Motor Rotation
- Thread starter chris kennedy
- Start date
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frenchelectrican
Senior Member
- Location
- Nord'est Wisconsin et Paris France
The most surefire way to verify the rotation on single phase motours is check the connection useally one of the starting and running winding always be 90? shifted so it can start that way.
to run other rotation all you have to switch start and run winding around that it. [ pretty common way with most single phasers ]
Merci,Marc
to run other rotation all you have to switch start and run winding around that it. [ pretty common way with most single phasers ]
Merci,Marc
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
chris kennedy said:
It really depend upon the type of single phase motor that you have.
For instance a small clock motor turns based on its construction, but a capacitor start motor turns based on the relationship between the separate start and run windings.
crossman
Senior Member
- Location
- Southeast Texas
First, for most single phase induction motors to be "self-starting" (to know which way to turn), we must somehow "split" the current into two out-of-phase currents. There are several ways to do this.
I'll start by discussing the "Shaded Pole" motor. The shaded pole motor consists of two "main winding poles" on the stator (It is possible to have more poles, but I'll stick with the simplest case of just two poles). Each of the main poles has a slot cut in it, and a piece of conductor is wound on the slot as shown in the drawing. This piece of copper is generally a single loop. If you will notice, essentially we have created a transformer with the main winding being the primary and the loop being the secondary. The loop is called a "shaded pole".
Looking at the main windings, and since this is single phase, as the sine wave changes positive and negative, the magnetic field simply swaps from north at top, south at bottom, to south at top and north at bottom. This magnetic field has no rotation, it just swaps back and forth, and the rotor has no idea which way it should turn.
For the motor to start, we must have a "rotating" magnetic field. This is where the shaded pole comes in. Since the shaded pole receives its current through induction, and since the shaded pole loop has different resistnace and reactance than the main windings, the current in the shaded pole will be out of phase with the current in the main windings.
Here is a diagram of the two currents:
Say we turn the motor on and say we are at the positive peak of the main winding sine wave (black). Let's say this creates a north pole at the top of the motor. The strongest magnetic field is going to be impressed from the main pole north at top to the main pole south at bottom, essentially the flux lines are vertical. But as time passes, the main pole current becomes weaker, and at some point the shaded pole current becomes stronger than the main pole = the shaded pole magnetic flux is stronger than the main pole magnetic flux. This would occur around the place where the "S" of the word "shaded" is in the diagram above.
Note that when the main pole current is zero, there is current in the shaded pole. So, the main pole magnetic field dies off and there is no longer a north at the very top of the motor. But the shaded pole current is still there.... and now the north magnetic field exists at the shaded pole. Essentially, the north pole has "rotated" from the exact top of the motor to a bit right of top. The magnetic field "rotates". And this is how a shaded pole motor starts.
The rotor will always turn toward the shaded pole. And, it is impossible to reverse a shaded pole motor - except they do make reversible ones which actually have a shaded pole on each side of each main pole and the shaded pole loops are actually made or broken through a switch, basically we choose which shaded poles to use.
Well, that is my view of the shaded pole motor. It certainly isn't gospel, and I welcome any comments.
Maybe we can tackle the "split-phase" motor soon?
I'll start by discussing the "Shaded Pole" motor. The shaded pole motor consists of two "main winding poles" on the stator (It is possible to have more poles, but I'll stick with the simplest case of just two poles). Each of the main poles has a slot cut in it, and a piece of conductor is wound on the slot as shown in the drawing. This piece of copper is generally a single loop. If you will notice, essentially we have created a transformer with the main winding being the primary and the loop being the secondary. The loop is called a "shaded pole".
Looking at the main windings, and since this is single phase, as the sine wave changes positive and negative, the magnetic field simply swaps from north at top, south at bottom, to south at top and north at bottom. This magnetic field has no rotation, it just swaps back and forth, and the rotor has no idea which way it should turn.
For the motor to start, we must have a "rotating" magnetic field. This is where the shaded pole comes in. Since the shaded pole receives its current through induction, and since the shaded pole loop has different resistnace and reactance than the main windings, the current in the shaded pole will be out of phase with the current in the main windings.
Here is a diagram of the two currents:
Say we turn the motor on and say we are at the positive peak of the main winding sine wave (black). Let's say this creates a north pole at the top of the motor. The strongest magnetic field is going to be impressed from the main pole north at top to the main pole south at bottom, essentially the flux lines are vertical. But as time passes, the main pole current becomes weaker, and at some point the shaded pole current becomes stronger than the main pole = the shaded pole magnetic flux is stronger than the main pole magnetic flux. This would occur around the place where the "S" of the word "shaded" is in the diagram above.
Note that when the main pole current is zero, there is current in the shaded pole. So, the main pole magnetic field dies off and there is no longer a north at the very top of the motor. But the shaded pole current is still there.... and now the north magnetic field exists at the shaded pole. Essentially, the north pole has "rotated" from the exact top of the motor to a bit right of top. The magnetic field "rotates". And this is how a shaded pole motor starts.
The rotor will always turn toward the shaded pole. And, it is impossible to reverse a shaded pole motor - except they do make reversible ones which actually have a shaded pole on each side of each main pole and the shaded pole loops are actually made or broken through a switch, basically we choose which shaded poles to use.
Well, that is my view of the shaded pole motor. It certainly isn't gospel, and I welcome any comments.
Maybe we can tackle the "split-phase" motor soon?
crossman
Senior Member
- Location
- Southeast Texas
Sorry, but I did not mention how the rotor becomes magnetized and all that, slip and everything, basically the magnetic flux of the stator cuts across the conductors in the rotor and induces current in the rotor.... like a transformer. The current in the rotor has its own magnetic field which interacts with the magnetic field of the stator.
mikeames
Senior Member
- Location
- Gaithersburg MD
- Occupation
- Teacher - Master Electrician - 2017 NEC
I was simply goign to post "phase shift from either from a cap or shaded pole" but your post is better.
ray cyr
Senior Member
- Location
- Yakima, Wash.
Crossman, thank you for that excellent explanation and for adding the graphics. I have a decent understanding of motor theory but that helped clarify the interaction of the main and shading poles.
Something along the same subject.....
Reversing motor rotations:
SHUNT OR SERIES:
Direct-current shunt motor may be reversed by the interchange of connections of either the field or the armature winding. Reversing the line leads will not change the direction of rotation.
COMPOUND MOTORS: D-C.
Interchange the connections of the two armature leads.
TWO PHASE INDUCTION MOTOR: (FOUR WIRE) Interchange the connections to the line of the two leads
of either phase.
TWO PHASE INDUCTION MOTORS: (THREE WIRE) Interchange the connections to the line of the two outside wires.
THREE PHASE MOTORS:
Interchange the connections to the line of any two leads.
SYNCHRONOUS MOTORS:
Ordinary synchronous motors are reversed in the same manner as induction motors.
FYNN-WEICHSEL MOTORS:
Interchange the connections to the line of any two of the motor leads and shift the commutator brushes to the same position on the opposite side of the field axis.
SINGLE PHASE INDUCTION, SHADING POLE STARTING:
The direction of rotation cannot be reversed.
SINGLE PHASE INDUCTION, INDUCTIVELY SPLIT'PHASE MOTORS:
Interchange the connections of either the main or the auxiliary winding.
SINGLE PHASE CAPACITOR MOTORS:
Interchange the connections of either the main or the auxiliary winding.
SINGLE PHASE INDUCTION, STARTED BY REPULSION ACTION:
Shift the brushes to the same position on the opposite side of the neutral axis.
SINGLE PHASE REPULSION MOTORS:
Shift the brushes to the same position on the opposite side of the neutral axis.
SINGLE PHASE SERIES MOTORS:
Interchange the connections of either the field or the armature winding. Reversing the line will not change the direction of rotation.
Reversing motor rotations:
SHUNT OR SERIES:
Direct-current shunt motor may be reversed by the interchange of connections of either the field or the armature winding. Reversing the line leads will not change the direction of rotation.
COMPOUND MOTORS: D-C.
Interchange the connections of the two armature leads.
TWO PHASE INDUCTION MOTOR: (FOUR WIRE) Interchange the connections to the line of the two leads
of either phase.
TWO PHASE INDUCTION MOTORS: (THREE WIRE) Interchange the connections to the line of the two outside wires.
THREE PHASE MOTORS:
Interchange the connections to the line of any two leads.
SYNCHRONOUS MOTORS:
Ordinary synchronous motors are reversed in the same manner as induction motors.
FYNN-WEICHSEL MOTORS:
Interchange the connections to the line of any two of the motor leads and shift the commutator brushes to the same position on the opposite side of the field axis.
SINGLE PHASE INDUCTION, SHADING POLE STARTING:
The direction of rotation cannot be reversed.
SINGLE PHASE INDUCTION, INDUCTIVELY SPLIT'PHASE MOTORS:
Interchange the connections of either the main or the auxiliary winding.
SINGLE PHASE CAPACITOR MOTORS:
Interchange the connections of either the main or the auxiliary winding.
SINGLE PHASE INDUCTION, STARTED BY REPULSION ACTION:
Shift the brushes to the same position on the opposite side of the neutral axis.
SINGLE PHASE REPULSION MOTORS:
Shift the brushes to the same position on the opposite side of the neutral axis.
SINGLE PHASE SERIES MOTORS:
Interchange the connections of either the field or the armature winding. Reversing the line will not change the direction of rotation.
wptski
Senior Member
- Location
- Warren, MI
480sparky said:
SINGLE PHASE INDUCTION, INDUCTIVELY SPLIT'PHASE MOTORS, the run and start windings aren't the same and/or use a different size wire plus a different turns ratio that's how the phase shift is created. Not sure how/if that could be reversed and work?
Split-phase:
Split-phase:
Generally you have two pairs of wires coming out. Just swap the leads on the start windings to reverse direction. Some motors have special connectors to make this easy.
Split-phase:
wptski said:SINGLE PHASE INDUCTION, INDUCTIVELY SPLIT'PHASE MOTORS, the run and start windings aren't the same and/or use a different size wire plus a different turns ratio that's how the phase shift is created. Not sure how/if that could be reversed and work?
Generally you have two pairs of wires coming out. Just swap the leads on the start windings to reverse direction. Some motors have special connectors to make this easy.
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