Although the invention is nearly 200 years old, the electric motor has actually enjoyed increasing popularity over the years. The main reason for this is its versatility. With fewer moving parts, quiet operation, easy scalability, and precise control, electric motors can be used in many more applications than any other type of motor. To get a better idea of how they do this, an understanding of the science behind them can help.
In the 18th century, early experimenter Andrew Gordon discovered that electrical currents in wires made them behave like magnets. It wasn’t until the 19th, though, that French scientist Andre-Marie Ampere figured out the actual relationship and developed the mathematical formulas, Ampere’s Force Law and Circuital Law, on which later advancements were based. Ampere discovered that electro-magnetic field intensity increased when electric current increased. He also found that magnetic polarity was connected to the direction the electric current was moving. Another key concept needed for electric motors was provided by Michael Faraday. Faraday discovered electro-magnetic induction whereby a magnetic field passes through a conductor and generates an electrical current in it.
Electricity Gets Moving
With this basic understanding established, it was Hungarian inventor Anyos Jedlik who built the first working electric motor with the primary components that are still present in some modern electric motors. In order to generate rotating movement, Jedlik invented the commutator. If you use an device with a rotating electric motor, for example an electric drill (read more info at TheDrillGuy), then you’ll be using a device that has not changed in its principle physics since the early discovery!
In its simplest form, the commutator consists of a metal ring with two gaps at opposite ends. The ring transfers electricity to the moving rotor by making contact with wire brushes attached to two parallel cables carrying power in opposite directions. When the rotor is repelled from one end of the fixed electro-magnet or stator and pulled towards the other end, the gap in the commutator allows the rotor to lose contact with one power line and draw power from the other line. This reverses the magnetic field, insuring the continuous movement of the rotor as it’s repelled from one end of the stator after the other.
To avoid the problem of brushes wearing out, most modern DC motors use external switches to reverse the polarity of the rotor or armature.
This type of construction works when the primary electric current is going in only one direction, such as with batteries. The electrical grid, though, uses an alternating current. Two inventors, Nikola Tesla and Galileo Ferraris, developed induction motors in the 1880s that could produce motion from AC power. They accomplished this by utilizing Faraday’s discovery. Since an alternating current drops to zero before building back up to full strength in the opposite direction, it provides the needed fluctuating magnetic field to induce an electric current in a secondary conductor in the rotor. This secondary current, in turn, creates its own magnetic field. The secondary magnetic field will always match the primary one, north to north or south to south, and will be repelled. As long as the current alternates, the rotor will continuously move.
While the invention of induction motors and expansion of the electrical grid led to a huge array of new devices like vacuum cleaners and dish washers, things didn’t end there. Computer advancements have made such things as printers or even robotics possible. Both rely on DC stepper motors. Likewise, improvements in battery technology make electric cars more practical over time. As important as electric motors are now, they’ll have an even bigger future.