- Published 23 Apr 2023
- Last Modified 20 Mar 2024
- 6 min
How Does an Electric Motor Work?
This guide will include how different kinds of electric motors work and how they are used.
Reviewed by Karl Ralph, Technical Support Engineer (November 2022)
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.
What are the Physics Behind an Electric Motor?
In the picture shown, imagine that the moving parts are the commutator and the rotor. The permanent magnets (stator), brushes and battery source (DC Volts) all remain static. The commutator is split into 2 half-moon connections which are connected to the square rotor wire creating an electrical circuit via the brushes to the DC Volts source.
The following sequence illustrates how the motor works:
- Electric current is passed through the rotor circuit from the battery (DC Volts) via the carbon brushes
- This current creates an electromagnetic field around the rotor. The north field faces the north field of the magnet, and the south field faces the south field of the other magnet
- The opposing magnetic fields cause a repelling force which pushes the rotor away from the magnets causing rotation in the direction of the arrow
- As the rotor turns past the point where the commutator contacts are split, the current flowing through the rotor will reverse
- The reversal in current will also reverse the magnetic field around the rotor and so continue to push the rotor around due to the repelling fields of the magnets. Rotary motion achieved
Types of Electric Motor
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:
- AC motors (induction, synchronous, squirrel cage)
- DC motors (shunt, series, separately excited)
- Other (universal, stepper, brushless)
Motor accessories can be useful in prolonging motor life and improving operating safety.
A/C Electric Motors
How does an AC electric motor work? AC electric motors convert alternating current into an alternating electromagnetic field. The alternating magnetic field is implemented in several ways to convert the alternating magnetic energy into motion.
- Induction (a magnetic field in the stator is induced into the rotor which then produces its own magnetic field)
- Synchronous motor (the rotor will rotate in sync with the revolving magnetic fields)
- Squirrel cage motor (this type of motor is like the induction motor except the rotor windings are replaced with solid bars which are connected and look like a squirrel cage. The alternating magnetic field induces a current within the bars which produce their own fields, creating motion)
Some of the larger more powerful motors will need motor starters. So how does an electric motor starter work? They operate similarly to a relay. Electric motor starters usually have a set of contactors that supply heavy current to the motor. There is a buttoned panel that you can use to start and stop the motor.
D/C Electric Motors
DC motors are probably the most common type of motor, due to their reduced cost vs an AC system. They consist of:
- Shunt motor (this is where the stator and rotor coils are connected in parallel)
- Series motor (the stator and rotor coils are connected in series. These types of motors have a very high starting torque and are typically used for overcoming high levels of starting inertia such as in electric trains, lifts, and other heavy load applications)
- Separately excited motors (Similar to shunt motors except that the rotor coil is powered separately from the stator coil. This has the advantage of facilitating speed control and reverse direction)
How Does an Electric Car Motor Work?
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.
How Does an Electric Fan Motor Work?
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.
How Does an Electric Bike Motor Work?
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.
Other Interesting Applications for Electric Motors
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 phone that is fitted with an off-balanced weight attached to the rotating spindle. This creates a vibrating action when the phone rings.
Electric Motors for Scooters
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.