Title: AC Motors and Reversing
Course: Electrical Motor Controls (Sandbox) > Section: Module 5: Reversing, 8 hr

What You Need to Know About AC Motors and Reversing

The following video gives a walk-through and explanation of the provided schematic which shows the power side and control side of a motor circuit with a reversing component.

Lecture Notes

Three-Phase AC Motors

In this course, we've been talking about a very common type of motor: a Three-Phase AC Motor. We've talked about power sources too, mostly 480 Volts AC. It's important to know that there are other types of electrical motors and other voltages that are used to run them.

At BTECH, we cover many different types of motors in detail in the course "AMAR 1550 - Electrical Motors and Drives". For now, we will stick with Three-Phase AC Motors, as shown below.

Reversing

The motor shaft in an electrical motor spins due to a magnetic interaction between a stator and the rotor.

Up until now, your motor control circuits have been running motors in a single direction. We'll call that direction "forward".

It's very common to give an operator a way to run a motor in both forward and reverse. A forward running motor may deliver a part to a machine, and reversing that motor might be how we retrieve the part from that machine.

The leads on a motor are marked T1, T2, and T3, and they are connected to the incoming power in this way:

P1 ------------> T1
P2 ------------> T2
P3 ------------> T3

This will run the motor forward.

A property of Three-Phase Electrical Motors makes it fairly easy to reverse: To reverse a three-phase motor, you just swap any two power leads. Therefore, to run the motor in our wiring example in reverse, you'd wire it up like this:

P3 ------------> T1
P2 ------------> T2
P1 ------------> T3

Below is a schematic that shows the power side and control side of a motor circuit with a reversing component. Please see the video for a walk-through and explanation.

Paraphrased from: Rockis, Gary J. and Mazur, Glen A.  (2009). Chapters 7 & 12. Electrical Motor Controls for Integrated Systems, 4th Edition.

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