ELECTRIC MOTORS
An electric motor, in its most basic definition, is a device that converts electrical energy to mechanical energy. Most electric motors operate off of Ampere's law, which was discovered in 1820 by Andre-Marie Ampere and states that a wire carrying an electric current produces a magnetic fields around itself. The interaction between the motor's magnetic field and winding currents generates the power for which will cause movement. As an electrical current is sent through the motor, a magnetic field is created around the wire. Since the loop itself has also become a magnet, one side will be attracted to the north pole (of the surrounding magnet) while the other end will be attracted to the south. Thus, causing the loop to rotate.
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| ELECTRIC MOTOR |
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| AMPERE'S LAW |
HISTORY
With the invention of the battery in 1800 by Allessandro Volta, the generation of a magnetic field from an electric current by Hans Christian Oersted in 1820, as well as the electromagnet in 1825 by William Sturgeon, the foundation for an electric motor was set. The basis of a motor was first demonstrated through British scientist, Michael Faraday's, experiment in 1821. Faraday placed a permanent magnet on a free-hanging wire that had been dipped into a pool of mercury Once an electrical current passed through the wire, the wire had begun to rotate around the magnet, illustrating a closed circular magnetic field around the wire. The following year, Barlow's wheel, built by Englishman Peter Barlow, became the first rotating device driven by electromagnetism. After numerous in vain attempts in trying to create an electric motor, German scientist Prussian Moritz Jacobi succeeded in creating the first real rotating electric motor. Following several more advancements, American scientist Thomas Davenport had been granted the first patent for an electric motor.
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| BARLOW'S WHEEL |
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| ELECTRIC MOTOR (PRUSSIAN MORITZ JACOBI) |
DC MOTORS vs. AC MOTORS
The direction of current flow is the fundamental difference between direct, DC, and alternating, AC, motors. In an alternating current, the direction of current flow changes back and forth at a rapid and constant rate. Current flows in AC motors initially travel in one direction through the wire loop and then reverse itself 1/60 of a second later. This attraction change from north to south pole occurs about every 1/60 of a second. Magnetic field changes are correspondent to current changes, therefore, the side of the loop that had been previously attracted to the south pole is now attracted to the north, and vice versa. Consequently, the loop receives another "kick", which twists it around its axis and helps continue the rotation.
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| ALTERNATING CURRENT MOTOR |
On the other hand, electric currents in DC motors always move in the same direction and due to this, the magnetic field will constantly point in the same direction, causing DC motors to stop their rotation after only half of a revolution. In order to solve this problem, the wire coming from the DC power source is attached to a split-ring commutator, a metal ring cut in half. Once the current begins to flow, it travels out of the battery, through the wire, and into one side of the commutator. The current then flows into the wire loop, producing a magnetic field. As the loop rotates, it takes the commutator with it. Once half of a revolution is completed, the current reaches the empty space and then travels onto the second half of commutator. As a result, the current starts to flow in the opposite direction, traveling through the loop and reversing the magnetic field. With the help of the split-ring commutator, a DC motor can be altered into an AC motor.
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| DIRECT CURRENT MOTOR |
PARTS OF AN ELECTRIC MOTOR
Rotor: In an electric motor, rotors are the moving parts, which turn the shafts to deliver mechanical power. Typically, rotors have conductors laid onto it to help carry currents that interact with the magnetic field and power the shaft
Stator: Stators are the stationary part of a motor's circuit. Usually containing windings or a permanent magnet, the core of a stator is comprised of laminations. Laminations, really thin sheets of metal, are used to help reduce energy losses that would occur if a solid core was used.
Air gap: The air gap is located between the rotor and stator and is generally as small as possible, which would reduce the negative effect on the motor's performance.
Windings: Windings in an electric motor are the wires that are laid in coils. Usually wrapped around a laminated magnetic core, windings help to create magnetic poles when a current is sent through it.
Commutator: A commutator is a mechanism used to switch the input of most DC motors, consisting of slip ring segments that are insulated from each other as well as from the motor's shaft.
