# Electric motors

### Electric motors

Electric motors are present in many areas of our everyday lives. Let's learn about the different types.

Physics

Keywords

elektromotor, electromagnetic induction, induction, engine, electric motor, AC motor, right-hand rule, electromagnet, magnetic field lines, induced current, direct current, coil, electric current, magnetic field, magnetic force, iron core, machine, energy, alternating current, electro, physics, electric, electricity

Related items

### Interaction between electric current and a magnetic field

• conductive wire
• magnetic induction lines - Imaginary lines used to illustrate the structure of magnetic fields. Their density indicates the magnitude of the magnetic field induction, while their direction indicates the direction of the induced current.

All electric motors utilise the magnetic effect of electric current.
When a current flows in a wire, a magnetic field is produced around that wire. The magnetic field has the same effect on a permanent magnet as another permanent magnet would, but this field is adjustable.
The strength of the generated magnetic field depends on the intensity of the current flowing in the wire and the distance from the wire, while its direction depends on the direction of the current.

### Looped wire

• conductive wire
• magnetic induction lines - Imaginary lines used to illustrate the structure of magnetic fields. Their density indicates the magnitude of the magnetic field induction, while their direction indicates the direction of the induced current.

### The coil as an electromagnet

• conductive wire - The strength of the magnetic field can be controlled by adjusting the strength of the electric current flowing in the wire.
• magnetic induction lines - They become concentrated inside the loops formed by a conductive wire, so the magnetic field will be stronger there.
• iron core - The strength of the magnetic field is influenced by the material composition of the core of the coil.

The magnetic field produced by the electric current can be strengthened by forming a loop in the wire, as this way the magnetic field lines become more concentrated inside the loop. The magnetic field can be further strengthened by forming a number of wire loops, that is, by forming a coil, and by wrapping it around a rod made of magnetisable material, for example, an iron core. The coil thus made is an electromagnet, which is found in all electric motors.

### Induction

• coil
• moving magnet
• ammeter

Electric current can induce a magnetic field, but a magnetic field can also induce electric current. This phenomenon is called electromagnetic induction.

Electric current can only be induced by a changing magnetic field. If the magnetic field in the environment of a coil changes, a voltage is induced in the coil and an electric current is generated. This current also produces a magnetic field, and the two magnetic fields can interact with each other.

### DC motors

• permanent magnet
• coil - When an electric current is fed into a metal coil, a magnetic field is generated around the coil, that is, it will function as a magnet: it will turn in order to align itself with the permanent magnetic field of the stator.
• commutator - The commutator rotates together with the rotor of the DC motor. It receives electric current through the brushes and transmits it to the coil(s) of the rotor. In the simplest DC motor there are two poles, therefore the commutator consists of two segments. As the commutator rotates, the poles of the electric current are switched every half turn.
• brush - Electric current is conducted to the commutator, then to the coil via brushes. They are usually made of carbon.
• iron core - The function of the iron core is to strengthen the magnetic field induced by the coil.
• insulation

There are two main types of electric motors: direct current (DC) and alternating current (AC) motors.

As their name suggests, DC motors are powered by direct current, which is either supplied by a battery or an external power supply. In the simplest DC motors, the stator is a permanent magnet and the rotor is an electromagnet, that is, a coil.

The current is applied to the rotating coil via carbon brushes and a commutator. As a result of the electric current supplied to the coil, the coil becomes a magnet. It turns in order to align itself with the polarity of the permanent magnet. However, before aligning itself in the correct direction, the polarity of the electric current in the commutator is reversed. Accordingly, the coil continues to rotate towards the opposite pole, and this is how it keeps on rotating.

It is common to use several coils in the rotor, so the commutator also has several poles, ensuring a smoother operation.

The disadvantage of DC motors is that the carbon brushes wear out, so they have to be replaced occasionally, and carbon dust particles that form can cause a short-circuit. In addition, DC motors are noisy too.

### AC synchronous motors

• rotor - The permanent magnet of the rotor tries to follow the rotating magnetic field of the stator.
• stator - The coils of the stator generate a rotating magnetic field.
• control electronics unit - It creates a phase difference between the coils.
• alternating current

The other main type of electric motors is AC motors which include synchronous and asynchronous motors.

In synchronous motors, alternating current, which changes direction periodically, is applied to the rotor. Such a current can be obtained either from the mains electricity or electronically. If the current in the coils of the stator does not alternate in the same phase, a rotating magnetic field is generated. The phase difference can be created either by using capacitors or more complex electronics. In most cases, there are permanent magnets in the rotor but there may also be coils (the latter supplied by direct current from an external supply). The magnet of the rotor tries to follow the rotating magnetic field of the stator, so it rotates with it.

Synchronous motors can only operate at a speed that corresponds to the frequency of the electric current that drives them. When a synchronous motor runs under load, the rotor falls back in phase by a certain angle relative to the stator pole, but they both run with the same synchronous speed. If the load is increased, the angle increases as well. If suddenly too much load is put on the motor, the rotor and the stator poles will fall out of synchronisation and the motor stops.

These motors are not self-starting, they require a starting mechanism. Most synchronous motors are started by an induction mechanism and only switch to synchronous mode when they reach the synchronisation speed.

When driving vehicles, the frequency of the alternating current supplying the synchronous motor is controlled electronically according to the desired speed of the vehicle. Since in modern electric vehicles alternating current is generated from direct current by an electronic circuit, these motors can be considered as DC motors. They are also called brushless DC motors or BLDC motors.

The advantages of synchronous motors over brushed DC motors are that there is no component in them that can wear out and produce dust; their operation is efficient and produces almost no noise at all.

### AC asynchronous motors

• rotor - It can also be a simple metal cylinder in which the electric current is induced by the changing magnetic field.
• stator - The coils of the stator generate a rotating magnetic field.
• control electronics unit - It creates a phase difference between the coils.

The principle of operation of asynchronous motors is based on the phenomenon of induction, so they are also called induction motors.

Asynchronous motors also consist of a stator and a rotor. The stator comprises several coils to which alternating current is applied. The rotor can be a metal cylinder, or a short-circuited coil, that is, one that does not receive current from an external source.

The operating principle of asynchronous motors is as follows:

1. The alternating current does not flow in the same phase in the coils of the stator, which induces a rotating magnetic field around the coils.

2. This rotating magnetic field induces an electric current in the rotor.

3. The induced electric current generates another magnetic field around the rotor.

4. The two magnetic fields interact with each other, so the rotor tries to align itself with the external magnetic field. However, since the magnetic field rotates, the rotor can never catch up with it, so it constantly revolves.

A rotating magnetic field is generated only when the electric current in the coils of the stator are in different phases. If polyphase power is used to drive the motor, the coils of the stator must be wired in different phases. If the motor is driven by single-phase power, then the phase shift of the external coils is controlled by capacitors or by more complex electronics.

The operation of asynchronous motors is less complicated than that of synchronous motors since they do not come to a stop when the load is increased.

### Linear motors

• stator - It consists of permanent magnets.
• rotor - It consists of coils.
• sensor

Both AC motor types have linear versions known as LIM (Linear Induction Motor) and LSM (Linear Synchronous Motor). The operation of these motors does not result in rotational movement, but to movement in a straight line.

Their principle of operation is the same as that of rotating motors, except that both the rotor and the stator are aligned along a straight line. Another difference is that the moving part is usually the one containing the coils and not the magnetic or magnetisable part.

In LIM motors, a polyphase alternating current is applied to the moving row of coils, creating a moving magnetic field that induces a current in the stationary metal rail, the magnetic field of which drives the moving part of the motor which contains the coils.

In the case of LSM motors, the rail must contain magnets in a row and the alternating current flowing in the coils of the moving part must be changed according to the direction of the movement so that it always reaches the next magnet in the correct phase. This is not possible without sensors and control electronics.

### Stepper motors

• rotor - It can also be a simple metal cylinder in which the electric current is induced by the changing magnetic field.
• stator - The coils of the stator generate a rotating magnetic field.
• control electronics unit - It creates a phase difference between the coils.

Stepper motors are very useful in devices where it is necessary to know the exact angle (or step) by which the motor rotates as a result of a certain amount of electric current.

Such motors move the arms of robots or the components of photocopy machines and printers. The rotor of stepper motors consists of permanent magnets, while the stator is made up of electromagnets. The electromagnets of the stator are supplied with current separately by the control electronics according to the desired angle.

The more permanent magnets are installed in the rotor and electromagnets in the stator, the smaller the angle at which the motor can rotate step-by-step, so that it can be rotated more precisely in the desired direction.

The resolution of the motor can also be increased if the magnets of the rotor and the iron cores of the electromagnets of the stator are toothed. The resolution can further be increased by precisely changing the control current fed to the coils.

### Narration

Electric motors are present in many areas of our everyday lives. Although there are various types, all of them utilise the magnetic effect of electric current.

When current flows in a wire, a magnetic field is induced around that wire. The strength of the generated magnetic field depends on the intensity of the current flowing in the wire and the distance from the wire.

The magnetic field generated by the current can be further strengthened by winding the wire into a coil. The coil thus made is the electromagnet which is found in all electric motors. The strength of the electromagnet and the position of its poles can be adjusted with the current flowing through it.

The electric current can create a magnetic field, but the magnetic field can also produce electric current. This phenomenon is called electromagnetic induction. Electric current can only be induced by a changing magnetic field. If the magnetic field changes near a coil, a voltage is induced in the coil and an electric current is generated. This current will have a magnetic field, so the two magnetic fields can interact with each other. Some electric motors utilise this phenomenon.

There are two main types of electric motors: direct current (DC) and alternating current (AC) motors. As their name suggests, DC motors are powered by direct current, their stator is a permanent magnet and their rotor is an electromagnet. The current is applied to the rotating coil through a sliding contact and carbon brushes. As a result of the electric current applied to it, the coil becomes a magnet. It turns in order to align itself with the polarity of the permanent magnet. However, before aligning itself in the correct direction, the polarity of the electric current in the commutator is reversed. Accordingly, the coil continues to rotate toward the opposite pole, and this is how it keeps the motor rotating.

The other main type of electric motors is AC motors, which include synchronous and asynchronous motors. In synchronous motors, alternating current, which changes direction periodically, is applied to the rotor. Such a current can be obtained either from the mains electricity or electronically. A simple electronic circuit ensures that the electric current does not alternate in the same phase in the coils of the stator, generating a rotating magnetic field. In these motors, the magnet of the rotor tries to follow the rotating magnetic field of the stator, so it rotates with it. Synchronous motors can only operate at a speed that corresponds to the frequency of the electric current that drives them. If suddenly too much load is put on the motor, the rotor and the stator poles will fall out of synchronisation and the motor stops. These motors are not self-starting, they require a starting mechanism. Most synchronous motors are started by an induction mechanism and only switch to synchronous mode when they reach the synchronisation speed. Since in modern electric vehicles alternating current is generated from direct current by an electronic circuit, these motors can be considered as DC motors. They are also called brushless DC motors or BLDC motors.

The principle of operation of asynchronous motors is based on the phenomenon of induction. They also contain two fundamental parts: a stator and a rotor. The stator consists of several coils to which an alternating current is applied. The rotor can be a simple metal cylinder, but it is usually a coil that does not receive current from outside; it will be induced in it. The alternating current in the coils of the stator does not flow in the same phase, so a rotating magnetic field is generated around these coils. This rotating magnetic field induces an electric current in the rotor. The induced electric current generates another magnetic field around the rotor. The two magnetic fields interact with each other, so the rotor tries to align itself with the external magnetic field. However, since the magnetic field rotates, the rotor can never catch up with it, so it constantly revolves. The operation of asynchronous motors is less complicated than that of synchronous motors since they do not stop when the load is increased.

Both AC motor types have linear versions too: LIM (Linear Induction Motor) and LSM (Linear Synchronous Motor). In these, the operation of the motor does not lead to rotational movement, but to translational. Their principle of operation is the same as that of rotating motors, except that both the rotor and the stator are aligned along a straight line.

Stepper motors are useful in devices where it is necessary to know the exact angle (step) by which the motor rotates as a result of a certain amount of electric current. Such motors move the arms of robots or the components of photocopiers and printers. The rotor of stepper motors consists of permanent magnets, while the stator is made up of electromagnets. The electromagnets of the stator are supplied with current separately by the control electronics according to the desired angle.

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