Electric Motors: How Do They Work?

What is an electric motor?

If you study the basics of electricity, you know that electricity and magnetism are, for the purposes of physics, united into one force called the electromagnetic force. An electric motor is a device that utilizes this force to produce mechanical energy.

In order to do this, the electric motor contains several components that utilize a electromagnetic field to create the mechanical energy. They come in many different sizes and configurations. Some electric motors are powerful enough to drive entire vehicles and others are so tiny that they can fit in the smallest electronic devices.

Electric motors are among the most efficient means of producing mechanical energy available and are utilized in an incredible array of roles, owing to that efficiency and to the fact that they are very durable devices.

Where Can You Find Electric Motors in Our Daily Lives and How Do They Help Us?

Electric motors can be found in a huge array of applications, right in the home. Every fan in any individual's home, for instance, likely contains an electric motor that propels the blades, converting electrical energy into mechanical energy and the mechanical energy of the blades into a breeze that circulates air around the room.

Electric motors can also be found in power tools. They power the bit in drills, the blade on circular saws and more. Their longevity and durability make them excellent solutions to this need, even in heavy industrial uses where other devices may not be able to hold up to the strain that electric motors can hold up to.

Electric motors that you probably never see greatly influence your everyday life. For instance, electric motors are utilized in most pump stations, which provide homes with running water. Electric motors are even used in very large ships, where they drive the screws that propel the vessel through the water.

Electric motors are so ubiquitous that it's hard to gather together even a few appliances without finding one that has an electric motor in it somewhere. From toys to the fans on air-conditioning and heating systems and beyond, electric motors are among the most common electrical components in use today.

History of Electric Motors

Like many electrical devices, electric motors started out as simple experiments and, once they were improved upon somewhat, they were used as demonstration devices for a time until they found practical applications.

The first electric motor is generally considered to have been developed by Andrew Gordon in the early 1700s. His electric motor was very simple compared to what is in use today.

In 1821, Michael Faraday, who is one of the most well-known names in all of electrical engineering, put together an experiment that clearly demonstrated the conversion of electrical energy into mechanical energy. While this may seem obvious enough a feat today, it was the foundation of what was to come.

Ányos Jedlik was a Hungarian physicist who, in 1827, started doing experiments with electromagnetic coils. He managed to construct what was called an "electromagnetic self rotor", which is really the first example of what we would consider to be an electric motor today.

Development continue to the 1800s on both direct current and alternating current versions of electric motors. The degree of efficiency and durability that modern people enjoy in electric motors is largely the result of continued experimentation that went on for nearly 100 years. As development continued, electric motors became more durable, more powerful and more reliable, eventually becoming the incredibly steady devices that are in common use today.

How Does an Electric Motor Work?

Electric motors work on a very simple principle. According to Hyperphysics, when an electric current is introduced into an magnetic field, a force is generated. An electric motor utilizes looped wires – the same wires that carry the current – which are stationed at right angles to the magnetic field in the electric motor. Because the magnetic field has dual polarities, each end of the wires is moved in a different direction. This creates a turning motion.

Torque is controlled by adding several loops to the armatures and the magnetic field is produced by an electromagnet. This design allows the rotor to be turned by simple electromechanical force, there are very few parts that actually experience any wear and, with those two factors combined, it's possible for electric motors to keep running for an incredibly long amount of time while exhibiting very little wear.

What are the Various Parts within an Electric Motor?

MotorsOne of the most remarkable things about electric motors is that they contain very few parts. Compared to, for example, an internal combustion engine, an electric motor is an incredibly simple device. In fact, all of the different parts of an electric motor could easily be pulled out and laid out on a very small table, depending upon the size of the motor, of course.

The stationary part of an electric motor is called the stator. The stator will be provided with permanent magnets or windings.

The windings will look familiar to anybody familiar with other electrical components. They are typically simple windings of wire around a magnetic iron core. When a current is passed through these windings, they generate a magnetic field. There are two different configurations for the field poles of the magnets in these devices. A salient pole device has a winding around the pole that lies below the face of the pole. A non-salient pole utilizes the pole face slots for the windings.

The rotor is the part that actually converts electrical energy into mechanical energy These come in various designs. One of the biggest breakthroughs in electric motor design was finding a way that the rotor could operate continuously, providing uninterrupted torque to whatever was being powered by the electric motor. Today's electric motors are capable of producing an incredible amount of torque.

The commutator is a device that is utilized to switch the input of the electric motor.

Believe it or not, the air gap in an electric motor is a viable part of the device, as well. The air gap is generally designed to be very small and, the smaller the air gap is, the better performing the electric motor will generally be.

Electric Motor Construction

Electric motors are simple in terms of the parts that they contain. The main parts are shown below.

  • The Frame: This is the container in which all the various parts of the electric motor are contained.
  • The Shaft: this takes the rotational energy from the electric motor’s spinning and provides a means to harness that energy via a mechanical connection: a piece of metal that extends through and outside of the frame.
  • The Stator: This remains stationary, usually constituting the field magnet for the electric motor. It may be a permanent magnet or it may be an electro magnet. Electromagnetic magnets incorporate a coil, usually made of copper wire.
  • The Commutator: Located near the Stator, this component reverses the current direction through the device. It is among the moving parts in electric motors.
  • Brush Assembly: The brush assembly contacts the Commutator and acts to complete the switch through which current flows.
  • Bearings: The Bearings on an electric motor are located near the point where the shaft exits the frame. This allows the shaft to spin with minimal friction and eliminates unwanted movement.
  • Armature: The Armature is a current-carrying component located in the center of the electric motor assembly. It interacts with the field magnet and winding to produce mechanical torque, providing rotation to the shaft.
  • End Bracket: The end bracket is attached to the frame at the shaft end of the electric motor, providing a means to secure the device and an opening for the shaft to pass through.

Starting the Motor

Electric motors utilize various starting mechanisms. In the simplest and smallest types, the starter may connect directly to a current source. Larger motors require more complex starters. They include:

DOL: Direct On Line starters connect to the power supply without any additional control devices. A DOL starter offers full load voltage to the motor as soon as it is turned on. The limitation in this method is that it offers no motor control. The motor will take off at full speed and torque as soon as power is supplied, which may transmit mechanical stress to the load.

Reduced-voltage (Soft Starter): A reduced-voltage starter allows the operator to start the device with a reduced voltage. The user can define the limits for startup current and other variables. The Star Delta starter is a type of soft starter that gradually increases the voltage to its maximum load as the motor increases its speed.

Reduced voltage starters have the advantage of allowing the mechanical stress and the torque output on the load to be controlled. Rather than the motor suddenly taking off at full torque and speed, as would be the case with a DOL starter, the motor gradually spins up.

Soft starters are commonly used in powerful motors. The reduced voltage only applies to the inrush current and is not used to control the speed of the motor. The reduced inrush current serves to prevent a sudden high-voltage draw on the electrical supply, which is required for compliance with power company guidelines, in many cases.

Variable Speed Drives: Variable speed drives, also called variable frequency drives, are commonly used with three-phase induction motors. These starters are used in electric motors of all sizes. The most significant advantage of this type of starter is that it allows the operator to increase or decrease the speed and torque of the motor by altering the voltage and the input frequency.

Circuit breakers are sometimes used to provide switching for electric motors, but usually only when there is a very large voltage applied to the device.

Advantages and Disadvantages of Motor Starter Types

DOL starting is mostly used on smaller devices. These include the motors that run water pumps and other simple machinery, which only needs to turn in one direction. Their primary advantage is in applying the full voltage to the motor instantly. The disadvantage is in the lack of control.

Soft starters are typically used on motors that require a large voltage draw. The gradual increase in voltage provides better control over electrical usage and eliminates the threat of suddenly applying a great deal of torque and rotation to the device.

Variable speed drives are the most complex of the motor starters, but offer the highest degree of control and functionality. In industrial settings, the control they offer over torque, tension, acceleration and flow can all contribute to more efficient and controlled processes.

What Types of Electric Motors Exist?

There are several different types of electric motors on the market. They can first be differentiated by whether they utilize AC power or DC power as their means of activating the motor. Further differences include whether the motor operates continuously – meaning that it rotates for as long as current is applied – or it operates in a step fashion, meaning that it turns to a position, stops and then remains there, not turning to a new position until current is applied again.

Some electric motors are outfitted with additional equipment – mainly gears – which make it easier for electrical engineers to install them on devices that they are building without having to fabricate the gear system on their own. These are available in a wide variety of different configurations and sizes.

Because there are so many different applications for electric motors, there are many different sizes of electric motors, as well. An electric motor may be not much larger than a fingernail or it may be large enough to take up an entire room, depending upon the application and how much work it is actually expected to do.

AC Geared Motors

AC geared motors utilize alternating current as a power source. The gear motor component provides a reduction gear train that allows engineers to more easily construct devices that call for a specific type of gearing. They are available in many different configurations and are used in a wide range of different applications, from large-scale industrial automation processes to constructing very small, compact devices, such as motors for toys and so forth.

AC Motors

AC electric motors are notable for being very low cost, very efficient and for being used in a wide variety of different applications. These utilize alternating current as their power source, and can be produced in very large sizes capable of handling significant loads. AC motors are utilized in a wide variety of different consumer devices, including record pliers, fans, power tools and so forth. They are also utilized in a great deal of industrial applications.

 

DC Geared Motors

Like AC geared motors, DC geared motors have a reduction gear train attached to the device. They are often utilized by electrical engineers because of the convenience of not having to construct the gear train themselves. DC motors utilize direct current as their power source and have their own advantages and disadvantages compared to alternating current powered electric motors.

DC Motors

DC motors come in many different designs. There are brushed DC motors, permanent magnet DC motors and more. What they have in common is that DC motors all utilize direct current as their power source. This makes them suitable for applications where alternating current may not be the ideal solution like Flat-screen TVs (AC goes into the TV, which is converted to DC). AC and DC electric motors were both experimented with around the same period – beginning in the early 1800s – and both have a wide variety of different applications.

Servo Motors

A servo motor is a sort of all-in-one device that has an electric motor – usually powered by DC power – a gear train, any integrated circuits required and a potentiometer included on the device. This makes them very flexible devices. They are used in a wide variety of different applications, including everything from industrial applications to model robot building. Servos are very easy to control and that control can be executed to a great deal of specificity. The servo sends constant feedback about its position, making them excellent for very precision applications.

Stepper Motors

Stepper motors are types of high precision electric motors. What differentiates these motors from other types of electric motors is that they do not operate in a continuous fashion. The motors steps from position to position, stopping each time it reaches a new position and then continuing the sequence. These motors are capable of moving in forward or backward directions and provide feedback that makes them very easy to control.

Stepper motors are often utilized in hard disk drives on computers, owing to the fact that they can stop in a needed position and that they activate and move as quickly as any other electric motor, which is almost instantaneously.