Brushed DC Motor: Working, Features & Applications

The brushed DC motor is one of the oldest motors and has the capacity to change the speed-torque ratio. It can provide three to four times more torque than its rated torque. It includes brushes for its commutator. It provides proper control of speed, and is driven by a direct current. These are affordable, easy to use, and have different shapes and sizes. Brushed DC motors have huge applications in home appliances and automobiles.

What is a Brushed DC Motor?

A brushed DC motor is a type of electric motor that runs on direct current (DC) and uses brushes to transfer electricity to the rotating part of the motor. These motors are known for their simple design, cost-effectiveness, and ability to provide strong torque at low speeds. Brushed motors are commonly used in applications like power tools, household appliances, and automotive systems.

While newer brushless motors offer longer lifespan and efficiency, brushed DC motors remain a reliable choice for many industries due to their straightforward operation and easy maintenance.

How does a Brush DC Motor work?

A Brush DC Motor operates based on the principles of electromagnetic induction and the interaction between magnetic fields and electric currents. Here’s a detailed explanation of how it works:

Basic Components of Brush DC Motor

1. Stator: The stationary part of the motor, which typically includes permanent magnets or wound field coils that create a magnetic field.
2. Rotor (Armature): The rotating part of the motor, which consists of windings that carry the electric current.
3. Brushes: Conductive materials (usually made of carbon or graphite) that make contact with the commutator to transfer current to the rotor.
4. Commutator: A segmented metal ring attached to the rotor shaft that switches the direction of current in the rotor windings as the rotor turns.
5. Shaft: The central part that rotates and transfers mechanical power.

Working Principle of Brush DC Motor

1. Electric Current Supply: When a voltage is applied across the motor terminals, electric current flows through the brushes and into the commutator.
2. Current in Windings: The current passes through the rotor windings, creating a magnetic field around the rotor.
3. Magnetic Interaction: The magnetic field created by the rotor interacts with the magnetic field of the stator. This interaction produces a force (torque) that causes the rotor to rotate.
4. Commutation: As the rotor turns, the commutator segments rotate past the brushes, periodically reversing the direction of current in the rotor windings. This ensures that the magnetic field produced by the rotor windings always interacts with the stator field in a way that maintains continuous rotation.
5. Mechanical Output: The continuous rotation of the rotor converts electrical energy into mechanical energy, which can be used to drive various mechanical loads.

How is a Brush DC Motor Controlled?

Brush DC motor speed control is simple, and does not require complicated electronics. The voltage applied to a Brush DC Motor is proportional to rotational speed. In other words, the higher the armature voltage, the faster the rotation. This relationship is linear to the Brush DC Motor’s maximum speed. By applying variable supply voltage, speed control can be achieved. Changing rotational direction can be done by reversing the field or armature connections.

In a Brush DC Motor, torque control is also easy to accomplish. Output torque is proportional to input current. Therefore, if current is limited, you have also limited the torque which the brush motor can achieve. Happily, variable speed or variable torque electronics are easy to design and manufacture. Varying the speed of a Brush DC Motor requires little more than an appropriate potentiometer.

Types of Brushed DC Motor

Brushed DC motors can be of two types based on stator construction, such as:

1) Permanent Magnet DC motor

For the purpose of producing the magnetic field against which the armature interacts, permanent magnet DC (PMDC) motors make use of permanent magnets. This design simplifies the motor structure by eliminating the need for field windings and the power supply that usually goes with them

Working Principles: Permanent magnets produce a magnetic field that the rotor, also known as the armature, places within to operate PMDC motors. The magnetic field of the stator generates a magnetic force that is perpendicular to the flow of current when current is flowing through the windings of the rotor. This phenomenon causes the rotor to experience torque.

Advantages and Limitations: PMDC motors have a number of advantages, the most significant of which is their relative ease of use and great efficiency. This is because they do not require any power to generate an external magnetic field. Temperature and age can also alter the magnetic strength of the permanent magnets, preventing them from producing a torque output beyond their capabilities.

These permanent magnet direct current (PMDC) motors are often more expensive than their wrapped stator counterparts. This is because high-quality magnets in the stator, such as neodymium, are more expensive.

Properties:

• Permanent magnet DC motors (PMDC motors) are the most common among all brushed DC motors.
• The inductor of this motor includes permanent magnets that create a magnetic field of the stator.
• It does not require high power.
• The torque of this motor is adjustable by the field of fixed magnets of the stator.
• It responds fast to the changes in voltage. It is easy to control the speed of the motor.

Advantages & Disadvantages

2) Wound Field DC Motor

Wound Field DC motor can be of three types based on the wiring diagram of stator winding.

i) Separately Excited and Shunt Wound Motor

• The currents of the field winding, inductor and armature are not dependent with each other in shunt wound brushed DC motor. The motor current is equivalent to the sum of the field winding current and armature current.
• The increase of supply voltage will increase the current. With the increase of the motor current, the speed will be maximized, and the torque will be decreased.
• If the motor load is increased, the armature current is increased and the armature field is increased. Once the armature current is increased, the inductor current is decreased that results a decrease in the inductor field and leads to a decrease in motor speed and an increase in torque.
• It has the torque and speed properties with the decrease of torque at high speed and fixed torque at low speed.
• It has huge applications in automotive industry.

Advantages & Disadvantages

ii) Series Wound DC Motor

• The field winding includes a series connection with the armature in a series-wound brushed DC motor.
• The excitation current is equivalent to the armature current in this motor.
• If the armature current becomes lower than the rated current, I_a < I_rat, and the magnetic system of the motor is not saturated, Ф ~ I_a under light loads,  the electromagnetic torque becomes proportional to the square of the current in the armature winding. The equation is the following:

M = c_M . F. I_a

where M is the motor torque in N∙m,

c_M is a constant coefficient determined by the design parameters of the motor,

Ф is the magnetic flux in Wb,

I_a is armature current, A.

Advantages & Disadvantages

iii) Compound Wound DC Motor

• Compound wound brushed DC motor has two kinds of field windings. One of those windings is connected in parallel with the armature winding, and the second is connected in series.
• The ratio between the magnetizing forces of the windings can be different. The winding that creates a large magnetizing force is known as main and the second winding is called as auxiliary.

Two types of Compound Wound DC Motor

1. Cumulative Compound Brushed DC motor:

• When windings are connected in a way that the series field supports the shunt field, then the motor is known as a cumulative compound brushed DC motor.
• Speed properties of cumulative compound brushed DC motor lie between speed characteristics of shunt-wound and series wound DC motor.

2. Differential Compound Brushed DC motor:

• When windings are connected in a way the two fields repel each other, then the motor is known as the differential compound brushed DC motor.
• If any constant rotational speed or an increase in the rotational speed with increasing load is needed to achieve, then the opposite connection of the windings is used.
• The performance of a compound wound DC motor is near to those of a shunt or series wound brushed DC motor based on which field winding acts as the prime role.

Advantages & Disadvantages

Performance characteristics of Brushed DC motor

The performance properties of brushed DC motors are determined by several factors, including their operating, electromechanical, and mechanical characteristics, as well as their adjustment properties.

1. Speed and Torque

Brushed DC motors are known for their ability to provide high torque at low speeds. Their speed can be easily controlled by adjusting the input voltage, which makes them ideal for applications requiring precise speed control.

2. Efficiency

While brushed DC motors are generally less efficient than their brushless counterparts, they offer good efficiency for most low to mid-range power applications. Efficiency decreases as the motor’s load increases, and mechanical losses due to friction in the brushes and commutator come into play.

3. Control and Adjustability

Brushed motors offer simple and cost-effective control methods. The motor’s speed can be easily adjusted by varying the voltage, and its direction can be reversed by changing the polarity of the voltage supplied to the motor.

4. Durability and Maintenance

Over time, the brushes in a brushed DC motor wear down due to friction. This requires periodic maintenance and replacement of brushes. However, when properly maintained, brushed motors can provide reliable performance for many applications.

These performance characteristics make brushed DC motors a popular choice for various applications, including automotive, small appliances, and consumer electronics.

The main parameters of the brushed DC motor

Torque constant: For a brushed DC motor, the torque constant is determined by the formula:

Where,

Z is the total number of conductors,

Ф is magnetic flux, Wb.

Where is the Brush DC Motor used?

Automotive

DC motors have been an essential component in the automotive industry, serving as the source of power for a wide number of applications. These applications include the propulsion systems found in electric vehicles (EVs) as well as a wide range of auxiliary systems. They meet the various requirements imposed by automotive technology due to their versatility, efficiency, and control features.

Industrial Machinery

In addition to being essential to the operation of a wide variety of industrial gear, direct current (DC) motors are also the foundation for the automation, control, and efficiency of a variety of production processes. The fact that they are able to provide exact control over speed and torque, in addition to their robustness and reliability, makes them a vital component in industrial settings.

Consumer Electronics

The consumer electronics industry widely uses DC motors to power a wide variety of products and appliances that consumers use on a daily basis. Because of their small size, high efficiency, and unique capacity to deliver precise control, they are ideally suited for a wide variety of applications within this industry.

Medical Devices

DC motors are an essential component in healthcare because they are the primary drivers of technological advancements and breakthroughs. Because of their precision, dependability, and controllability, they are indispensable in a wide variety of medical devices, ranging from diagnostic apparatus to machines that save lives.

Renewable Energy Systems

In the field of renewable energy, direct current (DC) motors are an essential component, as they contribute to the generation of clean energy as well as the efficient application of that energy. Because of their adaptability, efficiency, and control capabilities, they are essential components in a wide variety of renewable energy systems, which helps facilitate the shift towards sustainable energy solutions.