Electricity & Magnetism

Electric Motors: What Are They & How Do They Work?

Electric motors are used all the time to power devices we use every day. Whether it's a fan motor keeping you cool on a hot day, the motor in your leaf blower or an electric car, without electric motors, the world would be a very different place.

What Is an Electric Motor?

An electric motor is a machine that can convert electric energy into mechanical energy (specifically kinetic energy, or the energy of motion). This is typically achieved by exploiting the relationship between electricity and magnetism.

Electric motors may be powered by an AC current, such as that flowing from your wall outlet, or DC current such as that supplied by a battery.

How Does an Electric Motor Work?

The basic principle behind an electric motor is that there needs to be a coil of wire that is free to rotate in the presence of an external magnetic field.

As current is passed through the wire coil, the interaction between the current and the field produces a torque, causing the coil to rotate. This rotation can be used to rotate the tires on a toy car, for example, or it can drive a crank shaft, and convert the rotational motion into linear motion.

How to Make Your Own Electric Motor

Sometimes the best way to understand how a motor works is to build one yourself. You can build a simple DC motor with common household items.

By sending current through a carefully shaped wire in the presence of a magnetic field, we can create a portion of our circuit that will rotate, allowing us to convert electric energy into mechanical energy.

Things You'll Need

  • Winding wire
  • D cell 1.5-V battery
  • 2 paper clips
  • Permanent magnet
  • Tape

    Make a coil of wire by wrapping winding wire around a "D" cell 1.5-V battery a number of times (the battery serves as a form; remove the coil when done winding). Leave about 2 to 3 cm sticking out from both ends. Make sure that all of the turns are wound in the same direction.

    The coil should be well balanced on these ends so that it will turn easily when placed in the cradle provided by the paper clips. You should hold the coil together by twisting the last loop around the coils to wrap the coils together.

    When the coil is in the position shown, one of the wire ends, which will contact the paper clips, should have the insulation removed on the bottom side only. The other end should be completely stripped where it contacts the paperclip. This way, current will flow through the coil about half of the time.

    Bend two paper clips so that they will hold the coil as shown and secure them in place.

    Place a permanent magnet beneath your coil.

    Connect a power supply – such as the D battery that you used as the form – to the paperclips.

    Try to start your motor by giving the coil a small spin. Try, adjust, try, adjust, try and adjust again until you succeed!

How Does It Work?

If the coil is oriented as shown in the image, current is passing clockwise through the coil and the magnetic field points upward, then the top of the coil will feel a force pointing out (relative to the computer screen you are viewing this on), and the bottom of the coil will feel a force pointing in. This will cause the coil to rotate.

Once your coil has rotated 180 degrees, the current would then be flowing counterclockwise. However, since you have stripped half the wire, no current will flow during the time the coil is inverted. This is so that we don't end up with a force in the opposite direction making the coil reverse instead of continue.

Provided the initial push due to the field is strong enough, the coil will flip past 180 degrees, making a complete rotation, toward the end of which current flows in such a way that a force causes it to make another rotation just as before. If everything is balanced well enough, the motor should rotate fairly quickly and for a long time.

Commercial Motor Parts

Components of a commercial motor include the following:

The armature is the power-producing part of the motor. It may be located on the rotor (rotating part) or the stator (stationary part.) The armature consists of coils of wire that interact with the magnetic field when current passes through. In our homemade motor, the coil was the armature and rotor and the paperclips served as the stator.

Brushes allow for current to be transferred to the rotor as it rotates. In our homemade motor, the contact point of the paper clips and the copper wire served the same purpose.

A commutator serves to periodically reverse the current direction. This is needed in a direct current, or DC motor, but not usually in an alternating current, or AC motor because the current already changes direction. We achieved on/off current in our motor by keeping one side of the contact wire insulated.

A field magnet or field coils (electromagnets) create the necessary magnetic field.

The axle is a rod-shaped piece aligned with the rotor's rotation axis such that it rotates along with the rotor. The horizontal ends of our homemade motor were essentially an axle.

A pinion is a small gear that might be used to transfer the motor motion to another object or part of a machine.

Types of Electric Motors

There are many different types of electric motors. While first subdivided as AC or DC motors, many other variations are also possible. Whether for heavy duty, light duty, farm duty or general purpose, just a few of the many types are listed here.

A single-phase motor operates off of one AC power supply.

A three-phase motor is one which is driven by three alternating currents of the same frequency out of phase with each other.

A synchronous motor is a motor whose rotation period is an integer multiple of the AC frequency.

In an asynchronous or induction motor, the electric current in the rotor is generated by electromagnetic induction from the magnetic field of the stator winding.

A stepper motor is a brushless DC motor that breaks a full rotation into equal steps. The motor can move and hold at any one of the steps.

Electric Generators

Electric generators are the reverse of electric motors; they take mechanical energy and convert it into electrical energy. This can be done in many different ways.

For example, wind energy can be used to turn a wind generator's fan blades, which turn a rotor inside the generator, and the electromagnetic induction that results causes current to flow. Hydroelectric power plants work in a similar manner, with the falling water turning the blades in a turbine.

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