What is Inside a Motor [Take a look inside a AC and DC motor]

Ever wonder what’s going on inside of an electric motor? Or what it’s all made of? Well, we did, so we decided to take a look inside to see what exactly is inside an electric motor, what they’re made of, and what the difference is between AC and DC motor internals.

There are 5 main components inside an electric motor, depending on the type of motor. In DC motors there is an armature (rotor), brushes, a commutator, a stator winding or permanent magnets, and a shaft. In AC motors there are only two main components, they are the rotor and the stator windings.

In this article we will take a look inside both AC induction motors and DC electric motors to find out exactly what is inside of these incredible little machines.

exploded view of motor

There are eight different types of AC and DC motors overall, with each type having its own subset of variations, so as you can imagine there are quite a few different types of electric motors on the market. But as much as they vary, they all share common components for their basic operation.

motor maintenance pdf

Inside a DC motor

The 5 main components inside a DC motor are the armature also known as the rotor (rotating), the stator (stationary), the shaft, the brushes, and the commutator.

A DC motor works off the principle of electromagnetic induction. In the majority of DC motors, this is done by inducing a current into the armature of the motor via the brushes and commutator.

disassembled dc motor
DC motor internals

Once the armature is energized, it briefly creates a magnetic field which then interacts with the magnetic field of the stator’s permanent magnets, producing a rotating torque causing the armature to spin.

The other type of DC motor works by using replacing the stator’s permanent magnets with electromagnets and supplying the stator and armature with their own power supply. Once both the stator and rotor are energized two opposing magnetic fields will be produced causing rotation of the rotor.

Now lets take a look at each component on their own:

Stator

electromagnetic stator winding dc motor
Electromagnetic stator

The stator can be made in two different ways depending on the design of the motor. The most common stator design in a DC motor is by using permanent magnets all around the circumference of the stator frame. Permanent magnets will constantly produce a magnetic field without the need for a power supply.

permanent magnet stator motor dc
Permanent magnet stator

The second type of DC stator is constructed using electromagnets. Electromagnets are just simply coils of wire arranged in a specific order that when energized by an external power source, will create a magnetic field around the coils, this magnetic field then interacts with the magnetic field of the armature causing the armature to rotate.

Armature (Rotor)

he armature of a DC motor serves a critical role in the generation of mechanical power. It is a key component located on the rotor, which is the rotating part of the motor.

The primary function of the armature is to convert electrical energy into mechanical energy. It consists of wire coils or bars wound around a cylindrical core, usually made of iron or steel. The core provides structural support and helps in concentrating the magnetic field generated by the armature windings.

When a direct current (DC) is passed through the armature windings, it creates an electromagnetic field. This field interacts with the magnetic field generated by the stator (stationary part) of the motor, resulting in a torque that causes the rotor to rotate.

dc motor armature
DC motor armature

The armature windings are typically made of copper or aluminum due to their excellent electrical conductivity. These windings are insulated to prevent short circuits and are arranged in a specific pattern to facilitate efficient operation.

The number of armature windings and their arrangement, known as the winding configuration, can vary depending on the specific motor design and application requirements. Different winding configurations, such as lap winding or wave winding, offer advantages in terms of torque, speed, and efficiency.

Commutator

As mentioned previously, once the direct current (DC) supply is switched on, it energizes the armature windings and only briefly creates a magnetic field. This is due to direct current not producing a magnetic field because the current is direct and not alternating from positive to negative as is the case with AC power.

This would result in no interaction of magnetic fields, meaning no rotation of the rotor. That’s where the commutator comes in.

The commutator is an essential component found in DC motors. Its main purpose is to facilitate the flow of electrical current between the power source and the armature windings of the motor.

The commutator is typically a cylindrical, segmented device made up of copper or copper alloy segments. These segments are insulated from each other with materials such as mica. The number of segments corresponds to the number of armature windings.

dc motor commutator
DC commutator

The primary function of the commutator is to reverse the direction of current in the armature windings at specific intervals, ensuring continuous rotation of the motor. As the rotor spins, the commutator and brushes make and break contact with different segments of the commutator. This action effectively changes the polarity of the armature windings, ensuring a consistent rotational direction.

By reversing the direction of the current flow in the armature windings, the commutator allows for smooth and continuous rotation of the rotor. It ensures that the magnetic fields generated by the armature windings and the stator remain aligned, resulting in a steady torque output.

The materials used to construct the commutator, such as copper or copper alloys, are selected for their excellent electrical conductivity and mechanical durability. Copper is a common choice due to its high conductivity and ability to withstand the electrical and mechanical stresses encountered during motor operation.

Brushes

Brushes are important components in DC motors that play a key role in establishing electrical contact between the stationary part of the motor, known as the stator, and the rotating part, which includes the commutator and armature.

The brushes are typically made from carbon or graphite materials due to their excellent electrical conductivity and wear resistance properties. These materials can withstand the high current and friction generated during motor operation.

carbon brushes dc motor
Carbon brushes

Using carbon brushes in DC motors offers an additional advantage due to their negative thermal coefficient. As the temperature increases in the carbon brushes caused by friction, their electrical resistance decreases. This phenomenon enables easier and less restricted flow of current, contributing to improved electrical conductivity and motor performance.

The primary function of the brushes is to maintain continuous contact with the segments of the commutator, which is mounted on the rotor. As the rotor spins, the brushes slide against the commutator, ensuring electrical connection with the armature windings.

The brushes deliver the electrical current from an external power source, such as a battery or power supply, to the commutator. This current flow energizes the armature windings, creating the magnetic field necessary for motor operation. Simultaneously, the brushes collect the current that passes through the armature windings after the commutator has reversed its polarity.

It is worth noting that the brushes are subject to wear due to the friction and electrical arcing that occurs during operation. As a result, periodic inspection and maintenance of the brushes are necessary to ensure optimal motor performance. In some cases, brushes may need to be replaced when they become worn or damaged.

Shaft

The shaft in a DC motor serves as a mechanical link between the motor’s rotor and the external load or device it is driving. It is an essential component responsible for transmitting the rotational motion generated by the motor to the desired application.

The shaft is typically made from materials that possess excellent mechanical strength, durability, and resistance to wear. Common materials used for shaft construction include hardened steel alloys, stainless steel, or other high-strength metals or alloys.

The primary function of the shaft is to provide support and stability to the rotor assembly. It maintains the alignment of the rotor and ensures smooth rotation without excessive vibration or wobbling. Additionally, the shaft allows for the attachment of various components, such as the rotor core, commutator, and fan blades, depending on the motor design.

The choice of shaft material depends on factors such as the motor’s power rating, operating conditions, and the load requirements of the application. The selected material should have the necessary strength to withstand the torque and mechanical stresses exerted during motor operation.

Inside electric AC induction motors

AC motors are a much simpler design and only comprise of two main components, the rotor and the stator. This simple design is only possible due to the motor being supplied by an alternating current (AC).

How AC induction motors work is off the same principle of electromagnetic induction as DC motors do, but instead of energizing the rotor, it is the stator that is connected to the supply. Once the alternating current flows through the stator windings a rotating magnetic field is created around the stator coils.

This magnetic field then induces a current in the rotor which then creates its own magnetic field. These two magnetic fields then interact with each other causing the rotor to rotate.

Stator

The stator in an AC motor is a stationary component that plays a crucial role in the motor’s operation. It is typically made from durable and electrically insulated materials such as laminated steel cores and copper or aluminum windings.

ac motor stator winding iron core laminations
Stator windings

The primary function of the stator is to generate a rotating magnetic field when energized by an alternating current. It consists of a core, which is typically constructed from laminated steel sheets to reduce energy losses through eddy currents. The laminations help minimize magnetic hysteresis and improve the efficiency of the motor.

The stator windings are made are of copper or aluminum and are wound around the core in a specific pattern. When an alternating current flows through these windings, it creates a varying magnetic field that interacts with the rotor.

The rotating magnetic field generated by the stator induces currents in the rotor, enabling the motor to produce torque and initiate rotation. The stator’s magnetic field interacts with the magnetic field of the rotor to create the force necessary for the motor’s operation.

ac motor stator winding
Stator winding & iron core laminations

Additionally, the stator provides mechanical support and houses other components of the motor, such as the bearings and protective enclosures. It also acts as a heat sink, dissipating the heat generated during motor operation to maintain optimal performance and prevent overheating.

Rotor

In an AC motor, the rotor is the rotating component that works in conjunction with the stator to produce mechanical motion. The rotor is typically made from a solid iron core or laminated steel core, depending on the motor design and application.

The rotor differs from the armature of a DC motor in a few key aspects. In a DC motor, the armature is the rotating part of the motor that carries the conductors and windings, while the stator is the stationary part that consists of permanent magnets or electromagnetic poles. In an AC motor, the rotor is the rotating part, and there is no separate component equivalent to the armature of a DC motor.

ac motor rotor
AC rotor

The primary function of the rotor is to convert the rotating magnetic field generated by the stator into mechanical energy or rotational motion. The rotor contains conductive bars or coils that are connected to the motor’s power supply. As the rotating magnetic field of the stator interacts with the rotor, it induces an electric current in the rotor windings.

AC motor rotors can have different types depending on the motor design, including squirrel-cage rotors and wound rotors. Squirrel-cage rotors are the most common type and consist of short-circuited conductive bars or end rings. These bars or rings form a “squirrel-cage” shape, hence the name. Wound rotors, on the other hand, have windings similar to those found in DC motors, and they allow for more control over motor characteristics.

Squirrel cage rotor

The rotor’s interaction with the rotating magnetic field causes the generation of torque, enabling the motor to rotate. The rotor’s design, including the shape and arrangement of its conductive elements, influences the motor’s performance, efficiency, and starting characteristics.

Conclusion

In conclusion, understanding the internal components of AC and DC motors provides us with valuable insights into their operation and functionality. We have explored the significance of the stator and rotor in both motor types, where the stator, comprising of a core and windings, and the rotor, constructed from solid iron cores or laminated steel, form the fundamental building blocks of motor design.

Additionally, in the case of DC motors, we have examined the importance of the commutator and brushes in facilitating the conversion of electrical energy into rotational motion. By comprehending the role and construction of these components, we gain a deeper appreciation for the complexities involved in the motor’s ability to convert electrical power to mechanical output.

Gavin

I'm Gavin and Iv been teaching electrical science to apprentice electricians in a local technological university since 2022. I hold an Electrical Level 6 QQI Qualification along with several NZEB Certifications.

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