How does an ordinary DC motor work?

How does an ordinary DC motor work?

The simple motors you see explained in science books are based on a piece of wire bent into a rectangular loop, which is suspended between the poles of a magnet. (Physicists would call this a current-carrying conductor sitting in a magnetic field.) When you hook up a wire like this to a battery, a direct current (DC) flows through it, producing a temporary magnetic field all around it. This temporary field repels the original field from the permanent magnet, causing the wire to flip over. Normally the wire would stop at that point and then flip back again, but if we use an ingenious, rotating connection called a commutator, we can make the current reverse every time the wire flips over, and that means the wire will keep rotating in the same direction for as long as the current keeps flowing. That’s the essence of the simple DC electric motor, which was conceived in the 1820s by Michael Faraday and turned into a practical invention about a decade later by William Sturgeon. (You’ll find more detail in our introductory article on electric motors.)

Labelled diagram of an electric motor showing the main component parts.

Artwork: A DC electric motor is based on a loop of wire turning around inside the fixed magnetic field produced by a permanent magnet. The commutator (a split ring) and brushes (carbon contacts to the commutator) reverse the electric current every time the wire turns over, which keeps it rotating in the same direction.

Before we move on to AC motors, let’s quickly summarize what’s going on here. In a DC motor, the magnet (and its magnetic field) is fixed in place and forms the outside, static part of the motor (the stator), while a coil of wire carrying the electric current forms the rotating part of the motor (the rotor). The magnetic field comes from the stator, which is a permanent magnet, while you feed the electric power to the coil that makes up the rotor. The interaction between the permanent magnetic field of the stator and the temporary magnetic field produced by the rotor is what makes the motor spin.

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