So, what is an electric motor and how does it work? The main principle behind the operation of electric motors is that electrical energy is first converted into magnetic force and finally into kinetic energy resulting in physical motion. There are various ways in achieving this which gives us a multitude of motor designs, shapes, and sizes. There are also various ways in powering electric motors. Conventional AC and DC motors have been around for some time, but we now have access to advanced electronics to control motors. This gives us ultra-efficient motors that come with high levels of control.
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Some motors will operate using DC, some using AC, and some are controlled using signals or pulses. They also come in a wide range of sizes and power ratings. The three main types of electric motors are:
Motor accessories can be useful in prolonging motor life and improving operating safety.
Electric cars run on batteries which are a DC source. However, they can have AC or DC motors fitted. Where there is an AC motor, there are onboard inverter circuits to convert the DC from the batteries into alternating currents. The motors are usually AC induction types.
The onboard motor can also be used as a back-feeding alternator used for charging the batteries when the vehicle is descending a hill or braking. The disadvantage of using AC motors in cars is that they tend to be more expensive to implement than DC motor systems.
A larger electric fan is often powered by an induction motor. Smaller handheld fans have DC motors. Single-phase induction motors in fans can be fitted with starter capacitors. These are wired in series with the stator and rotor coils to provide out-of-phase current. The capacitors enable the motors to start up easily and can facilitate speed control. The capacitors are used to improve the starting and running performance of single-phase motors and they also ensure the motor runs in the correct direction.
In electric bikes, the motors favoured are permanent magnet and brushless DC motors. They are commonly 3-phase motors (they have 3 stator coil windings). These are powered and controlled by onboard electronics which supply pulses to regulate power and speed.
Electric motors are used almost everywhere you look. It’s hard to imagine how we would function without them. They are used in washing machines, toothbrushes, fridges, cars, bikes, robotics, hard drives, hair dryers, lathes, cranes, ships, trains, drones, and the list goes on.
Motors can even be found in our mobile phones for creating vibration. In this application, there is a tiny electric motor mounted in the that is fitted with an off-balanced weight attached to the rotating spindle. This creates a vibrating action when the rings.
These are fitted with at least one brushless DC motor (BLDC). These are electronically controlled like bike motors. They are extremely efficient and will offer an incredible amount of power relative to their size and weight.
Motors are indispensable items in today's world. With advancing technology, they will continue to evolve and contribute favourably to our modern way of life.
The majority of industrial motors are three-phase AC induction motors due to its reliability and low cost.
In this case, the electric current in the stator winding generates a rotating magnetic field that "induces" (hence the name) electric current in the rotor. The current induced in the rotor create a magnetic field that reacts against the stator field, generating rotation in the rotor. An induction motor has to operate at a slightly lower than synchronus speed, given that rotation at synchronus speed would result in no induced rotor current.
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This is why induction motors are called asynchronous, because the rotor rotates slower than the stator's rotating magnetic field to produce torque about the output shaft.
If the rotor is rotating faster than the stator's rotating magnetic field, current will be induced in the stator. In this scenario, induction motors can act as generators.
Induction motors are inexpensive because they only require electromagnets in the stator and rotor to operate. They are also reliable because they do not need commutators to transmit current to the rotor, mitigating the possibility of arcing and frictional wear.
Most industrial facilities use induction motors due to their desirable characteristics such as reliability, simplicity, and affordability.
For synchronous motors the rotation of the shaft is synchronized with the frequency of the current supplied to the motor. The stator of the motor contains electromagnets that create a magnetic field, which rotates according to the characteristics of the current applied to it. The rotor contains permanent magnets or electromagnets that react against the magnetic field generated in the rotor, generating rotation of the shaft. The rotor requires a physical connection to electric power by the means of a commutator, usually consisting a conductive brush that can wear out from use.
These motors are called synchronous because the rotor rotates at the same speed as the stator's rotating magnetic field.
Although less commonly used due to higher cost, AC synchronous motors exhibit higher power efficiency than AC induction motors.
AC synchronous motors are unique in the fact that they can be used to correct the power factor of an industrial facility.
DC motors are the least commonly used type of motor, succeeded by the advent of modern AC motors.
The stator produces a static magnetic field while the rotor produces a rotating magnetic field powered by a commutator.
As a result, the rotor's magnetic field attempts to align with the stator's magnetic field which produces torque about the output shaft.
Rather than utilizing electromagnets to produce a static magnetic field, permanent magnet DC motors use magnets to create the field. Since the magnetic field is always present regardless of the motor's power state, permanent magnet motors may attract other nearby ferromagnetic materials, creating a potential risk in an industrial setting.
Permanent magnet DC motors are also heavier and bulkier due to the use of magnets in the stator.
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