How Do Electric Motors Work
It seems magical that it takes just a flick of a switch to turn on electricity. To remote villagers and ancient people, the ability to use electricity would have seemed like a miracle. Today, electric motors run a surprising number of appliances and vehicles. While electric motors are small, they carry a significant amount of power. Each motor is packed with large magnets and wound copper in a small design. Depending on the design, the windings may rotate around the magnets or the magnets may rotate around the windings. Brushless DC motors offer a higher efficiency and more torque per watt.
How Electricity, Movement and Magnetism Work
At the most basic level, an electric motor is just a metal rod that rotates to create power. The metal rod is known as an axle, and it moves a loop of wire through two different poles. Centuries ago, inventors figured out that a horseshoe magnet and copper wire could create electricity. The wire was placed between two poles of a horseshoe magic and run in a circle. As it moves, an electrical current is created that makes a magnetic field. If a wire is placed near the magnet, it interacts with the field. The temporary magnetism on the wire is the cause of the electrical current.
In 1820, French physicist Andre-Marie Ampere figured to the basic science that runs electric motors. Andre-Marie Ampere wrote that a magnetic field and an electric current could theoretically interact with each other. While the earlier discovery was important, it was not enough to create the electrical mowers and dishwashers that society has today. One year later in 1821, Michael Faraday proved that this was possible. Faraday placed a hanging wire dipped in mercury on a permanent magnet. Whenever an electrical current moved through the wire, the wire would turn the magnet. These early designs became the basis for the modern electrical motor.
Imagine a wire that is built into a U-shaped loop so that there are basically two parallel wires forming the sides of the U. One of these wires brings electricity away from the wire, and the other wire brings electricity back. According to Fleming's Left-Hand Rule, the two wires will move in opposite directions because the current is flowing in different directions. When the electricity is turned on, one of the wires will move up. The other wire will move down.
If the coil of wire was left on, it would theoretically rotate forever. With this basic setup, the wires would get tangled up before long. In addition, the coil could flip over if it reached a vertical position. If this happened, the coil would reverse and rotate in the opposite direction. This would obviously make it an ineffective motor because the motor would just undo and redo each action. For example, a train running on this basic setup would just move slightly forward and slightly backward forever.
How Real Electric Motors Work
Since the most basic way to create electricity does not make an effective motor, inventors had to figure out an alternative solution. One of the most popular ways to produce an electric current is with alternating current (AC) systems.
For this type of system, a small, battery-powered motor uses a device called a commutator on the coil's ends. The commutator looks like a metal ring that is separated into two halves. It works to reverse the coil's electric current every time the coil finishes half of a rotation. Each half of the coil is attached to one end of the coil. Meanwhile, the batter's electric current is linked to the motor's electric terminals. Electric power is pushed into the commutator through loose connectors. Known as brushes, these connectors are made out of materials like springy metal or graphite. Once the commuter has been attached, electricity flows through the circuit to cause the coil to rotate.
Improving the Motor
To make more power, a better motor had to be created. Later developments used more powerful magnets, more loops in the coil and increased electrical current. When an electric motor is made, there are certain ways that it can be made more powerful. If the magnet and coil are placed as close together as possible, it causes more force to be produced.
The Main Parts of an Electric Motor
While motor designs can vary, there are a few common components. Each motor needs to have a magnet to create the electricity with a coil around it. This coil has to be placed on an axle so that it can be spun at a high speed. Meanwhile, a commutator is attached to the coil. The rotating parts of the motor like the coil are known as the rotor. Stationary parts like the magnet are called the stator because they are static.
The parts of a motor include the:
Air Gap: This is not technically a part, but it is a part of every motor. The air gap is the distance between the stator and the rotor. Ideally, the air gap is as small as possible so that the motor generates the maximum amount of power.
Rotor: A rotor consists of the coil, axle and commutator. This section of the motor turns the shaft and creates power. Conductors are often placed in the rotor to carry electrical currents and interact with the magnetic field.
Windings: The windings are the wires that are wound into coils. Often, these wires are wrapped in a laminated soft iron magnetic core to create magnetic poles.
Stator: This section of the motor is static and contains a permanent magnet or windings. The core of the stator is made of very thin metal sheets that are known as laminations. These laminations are responsible for limiting energy losses that would normally happen with solid cores.
Commutator: The commutator is a device that can switch the input of some DC and AC machines. It looks like a segmented metal ring and connects to either pole. Without a commutator, the motor would just stop after a short period of time.
Other Types of Electric Motors
In a DC motor, the rotor spins inside a stator. AC motors work by passing alternating currents between opposing pairs of magnets. The rotation creates a magnetic field that causes the AC motor's rotor to spin. Often, AC motors are used for industrial machines and magnetic levitation railroads.
One of the most interesting motor designs is the DC motor. This type of motor works by getting the rotor and stator to swap back and forth. Multiple iron coils remain in place in the center of the motor, and the actual magnet rotates around them. In essence, the DC motor has the opposite design of an AC motor. While the wires rotate in an AC motor, it is the magnet that rotates in a DC motor.
The Brushless DC Motor
Also known as an electronically commuted motor, the brushless DC motor was one of the most exciting developments in electric motors. It uses a synchronous motor that is powered by a DC electric source. An integrated inverter helps to create an AC electric signal to power the motor. The output from the inverter controls the frequency, amplitude and waveform.
Within the rotor, the brushless DC motor uses a permanent magnet that rotates around a fixed armature. This means that the motor does not have any problems with connecting the current to the rotating part of the motor. Instead, it uses an electronic controller instead of the typical commutator. Phases are continuously switched so that the windings continue to turn the motor.
Unlike brushed DC motors, the brushless motor offers more torque per watt and a high torque to weight ratio. As a result, it has a longer lifetime, better reliability and reduced noise. Since it does not have any commutators, it does not produce ionizing sparks and has limited electromagnetic interference. In addition, the lack of windings on the rotor means that this motor does not have to deal with centrifugal force. Windings are supported by the housing, so airflow is not needed to cool the motor. Instead, the motor can be entirely enclosed and protected from dirt. The only limit to the brushless DC motor's power is heat. As long as the heat level is kept down, it can produce as much power as necessary.
How Is Electricity Converted Into Mechanical Energy?
Electromagnetism is the reason why motors create electricity. Originally discovered by Michael Faraday, electromagnetism occurs when a changing magnetic field creates voltage. Electromagnetic induction is created when a magnet or a coil rotates around the other item. The amount of the voltage depends on the speed of movement and the number of loops in the coil of wire. If there are more coils or a faster moving magnet, the motor will produce a higher voltage. The entire system works because of the opposite magnetic poles that force the wire to continue turning.
Without the electric motor, many of the technologies of the last century would never have been made. From electric generators to blenders, the modern world runs off of electric motors. Modern devices may bear a resemblance to early motors, but they are far more efficient at producing power.