What is the Difference Between AC and DC Electric Motors?

Electric motors convert electronic energy into mechanical energy, using either AC or DC electricity. AC and DC electric motors are constructed differently and have different properties. To fully understand the difference between AC and DC electric motors, electricity itself must be understood. Electricity is a very different energy source to heat or light as it is not commonly found in nature. Electric current refers to the movement of electrons along a conductor, such as a wire. The terms AC and DC refer to the direction of the electrons along the conductor.

In an AC motor the electrons flow along an alternating current and in a DC motor the electrons flow along a direct current. The direct current in DC electric motors means that the electrons constantly flow forwards, whereas in AC motors, the electrons switch directions regularly, so that they flow alternatively forwards and backwards.

Electricity and magnetism are closely linked and DC electricity was initially discovered, by Thomas Edison, by placing a magnetic field close to a wire and observing the electrons in the wire flow in a direct current as they were repelled and attracted by the north and south poles of the magnetic field. AC power was discovered by the scientist Nikolas Teklas by applying a rotating magnet to a conductive wire. Teklas found that as the magnet rotated the flow direction of the electrons flipped around, and that this method of alternating current retained energy better than the direct current and enabled the transferral of different amounts of power.

AC electric motors consist of two parts, the external stator that produces a rotating magnetic field and the internal rotor that receives a torque from the rotating field. AC motors come in two different types, depending on the rotor used. One type is the induction motor, which uses an induced current to produce a magnetic field on the rotor and can only run slightly slower or faster than the supply frequency. The other type of AC electric motors is the synchronous motor which does not rely on an induced current, and can rotate at exactly the supply frequency speed.

DC motors are made up of six components, a rotor, commutator, axle, brushes, a field magnet and a direct current power supply. DC motors are available in two main categories, being brushed and brushless. Brushed DC electric motors offer high reliability and simple control of motor speed. The initial cost of brushed DC motors is low, but with the higher maintenance involved in replacing brushes and springs, the price can rise. Brushless DC motors use an external electronic switch synchronised with the rotors position. Brushless DC motors are generally used where precise control of motor speed is needed.