Electric motor

An electric motor is a sophisticated machine designed to convert electrical energy into mechanical energy. This conversion process allows electricity to perform physical work, such as spinning a shaft or moving a component. Most motors operate through the interaction between a magnetic field and an electric current. This interaction generates a force known as Laplace force, which creates torque on the motor's shaft.

Because they produce linear or rotary force to move an external mechanism, motors are classified as a type of actuator. While they are usually designed for continuous rotation, they can also be used for linear movement over significant distances.

To understand how a motor works, one must look at its two primary mechanical components: the rotor and the stator. The rotor is the part that moves to deliver mechanical power. The stator is the part that remains stationary and surrounds the rotor.

Electrically, the motor functions through a magnetic circuit consisting of field magnets and an armature. The field magnets, which can be permanent magnets or electromagnets, are typically located on the stator. The armature, which consists of wire windings on a ferromagnetic core, is usually attached to the rotor. When electric current passes through the armature windings, the magnetic field from the stator exerts a Lorentz force on the wires. This force causes the rotor to turn.

Engineers carefully manage the physical construction of these parts to ensure efficiency. A small air gap is maintained between the stator and the rotor to allow movement. This gap must be kept as small as possible because a large gap weakens the motor's performance. However, if the gap is too small, it may cause noise or friction. The stator core is often built from many thin metal sheets called laminations. These laminations are made of electrical steel and are insulated from each other. This design reduces energy losses caused by induced circulating eddy currents that would occur in a solid core.

In some motors, such as those used in washing machines, the stator is encapsulated in plastic resin to prevent corrosion or noise.

In many direct-current (DC) motors, a specific component called a commutator is required. The commutator is a rotary electrical switch that supplies current to the rotor. It consists of a cylinder made of multiple metal contact segments. To deliver electricity, two or more conductive brushes, often made of carbon, press against the commutator.

As the shaft rotates, the brushes make sliding contact with successive segments. The commutator is essential because it periodically reverses the direction of the current in the rotor windings every 180 degrees. This reversal ensures that the torque is always applied in the same direction. Without this mechanism, the direction of the torque would reverse every half turn, causing the rotor to stop.

There are several ways to classify motors based on their design and motion. Motors can be powered by direct current (DC) from batteries or alternating current (AC) from a power grid. They can also be categorized by their construction, such as being brushed or brushless. Some motors use a salient-pole configuration, where the cores have projections called poles that face each other. Others use a nonsalient-pole design, where the core is a smooth cylinder with windings distributed in slots.

Motors may also be cooled by air or by liquid depending on their intended use.

The history of the electric motor is a timeline of many scientific discoveries. Early experiments in the 1740s involved electrostatic motors, which relied on electrostatic force. These were difficult to use because they required very high voltages. In 1820, Hans Christian Ørsted discovered that electric current creates a magnetic field. This led Michael Faraday to provide the first demonstration of rotary motion in 1821. He used a wire dipping into a pool of mercury near a permanent magnet.

Later, in 1827, Ányos Jedlik invented the commutator, which allowed for continuous rotation. By 1834, Moritz von Jacobi created a powerful motor capable of driving an electric boat.

Today, electric motors are vital to modern civilization and appear in many different scales. Large-scale motors are used for marine propulsion and pipeline compression, with outputs exceeding 100 megawatts.

On a much smaller scale, tiny motors can be found inside electric watches.

Motors also power household appliances, power tools, and vehicles. Interestingly, some motors can operate in reverse to act as generators. In systems like regenerative braking in vehicles, the motor converts mechanical energy back into electrical energy. This process recovers energy that would otherwise be lost as heat and friction.