Electric Motor Reversing Theory

OliLt · Sep 26, 2020

I posted this question in another post, but it was never answered. I am asking the question again as a new post. I have been following the motor reversing threads with great interest. If I understand everything correctly, swapping the leads to the start windings will reverse the rotation of a single phase induction motor with a capacitor in most cases. What I don't understand is that unlike DC voltage, AC voltage has no polarity. Why would swapping the leads to the start windings reverse the rotation? Thanks in advance.

Stephen Newell · Sep 26, 2020

Someone else will explain it better. The motor is an electro magnet. It's wired to create a magnetic field which causes the motor to turn in one direction. To reverse it you change the wiring so the magnetic field is reversed.

Roger Tomfohrde · Sep 26, 2020

Think of it this way, draw a large W over the top of a M. Label the top two lines M1 and M2 and the bottom ones S1 and S2. Now this will be at the time current hits but if you draw a line from M1 and S1 to a third connection labeled L1 and another line from M2 and S2 to N the motor will start in that direction because the ends are at the same polarity. Reverse is M1 and S2 and M2 to S1 the motor will reverse because you have changed the polarity of the windings. The only other way of reversing a motor is by reversing the stator.

buickanddeere · Sep 26, 2020

Swapping the polarity of the start winding with relation to the run windings .

JMOR · Sep 26, 2020

didnt get an answer this time either, did you? As soon as an "explanation" on an AC motor uses the word "polarity", just hit DELETE.

teddy52food · Sep 26, 2020

But, AC has no polarity!

Janicholson · Sep 26, 2020

AC sure has polarity. That it changes 120 times per second 60 Hz. does not mean that it it should not be considered. When the hot leg is in a voltage + rising mode. The polarity of any winding attached matches that current flow. The motor runs CW. If we wait till the Hot leg is voltage - rising, it still runs CW because all connected or inducted magnetic fields are still in phase. If we reverse the leads on the starting windings, the motor spins the opposite way. This is true for specific classes of capacitor start, induction run motors. The motor design might favor one direction over the other due to the EMF/Back EMF design of the rotor laminations (often a spiral rather than straight) Magnetic reluctance, Eddy currents, Henrys, and hysterisis are all involved. Jim

buickanddeere · Sep 26, 2020

(quoted from post at 13:29:16 09/26/20) didnt get an answer this time either, did you? As soon as an "explanation" on an AC motor uses the word "polarity", just hit DELETE.

Read my answer again and think about it.

Roger Tomfohrde · Sep 27, 2020

Easier to show on 240 because L1 and L2 are different polarity to each other at the same instant of time.

Case Nutty 1660 · Sep 29, 2020

not sure this adds to the post but I have a seed cleaner with a reversible AC motor,, never seen another like it that i remember other than on some stacking conveyor wheel motors on the crusher where I worked years ago, but those may have been DC cant say now they powered the one wheel to move it to change where it dropped material ,, has a three position toggle switch,,,

Electric Motor Reversing Theory

OliLt

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Stephen Newell

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Roger Tomfohrde

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buickanddeere

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JMOR

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teddy52food

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Janicholson

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buickanddeere

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Roger Tomfohrde

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Case Nutty 1660

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