Understanding Electric Motors

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MOTOR BASICS

BASIC COMPONENTS

*

Armature - Sometimes called a rotor. This is the part that spins. The armature can be either a permanent magnet or an electromagnet.

* Stator - This is the part that doesn't move. The rotor spins in the magnetic field contained in the stator.

HOW WORKS A MOTOR?

The force that that turns the armature comes from the magnetic field of the armature trying to line up with the external magnetic field of the stator. This force is called torque. This torque will cause the armature to turn until its magnetic field is aligned with the external field, but no further. How does the armature continue to spin? One of the magnetic fields must be changed so that the armature has to turn again. The armature will spin so long as there is always a torque acting on it. How this is accomplished is what sets each type of electric motor apart.

DIRECT CURRENT MOTORS

SIMPLE DIRECT CURRENT MOTOR

In a DC motor, the armature consists of any number of windings, each one an electromagnet. The armature is immersed in a directional external magnetic field. This external field does not move, and can come from permanent magnets or electromagnets.

A direct current in a set of windings creates a polar magnetic field. A torque acts on the rotor due to its relation to the external magnetic field. Just as the magnetic field of the rotor becomes fully aligned with the external magnetic field, the direction of the current in the windings on the armature reverses, thereby reversing the polarity of the rotor's electromagnetic field. A torque is once again exerted on the rotor, and it continues spinning.

The change in direction of current is facilitated by the split ring commutator. The brushes remain stationary, but they are in contact with the armature at the commutator, which rotates with the armature such that at every 180° of rotation, the current in the armature is reversed.

BRUSHLESS DIRECT CURRENT MOTOR

A brushless DC motor has a permanent magnet or magnets for the armature. The external magnetic field comes from any number of electromagnets that are turned on and off at the correct times by a timing device.

The exact workings of different brushless DC motors depend on the type of timing device used. This example uses a Reed switch.

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