Brushed DC Motors: Working Principle, Key Features, and Drive Circuit Design
This in-depth guide explains how a brushed DC motor works, its structural features, and the drive circuits that make it run efficiently.
Darren Yi
sales@zmartechome.com
Brushed Direct Current (DC) motors have been a cornerstone of electromechanical systems for more than a century.
Despite the rapid rise of brushless DC (BLDC) motors in modern appliances and industrial automation, brushed DC motors remain relevant due to their simplicity, cost-effectiveness, and ease of control.
Whether you are an engineer, hobbyist, or product designer, understanding these fundamentals will help you select and integrate the right motor for your application.
1. Overview of Brushed DC Motors
A brushed DC motor converts electrical energy into mechanical rotation using a direct current power supply.
Its name comes from the use of carbon brushes that physically contact a commutator, enabling current to flow into the rotating armature while reversing polarity at the proper moment.
Brushed motors are widely used in:
- Household appliances - vacuum cleaners, hair dryers, blenders, and power tools
- Automotive systems - wiper motors, seat adjusters, window regulators
- Industrial equipment - conveyors, actuators, pumps, and small automation devices
- Toys and hobby projects - RC cars, robotics kits, model trains
Their ability to provide high starting torque and smooth speed control makes them attractive in many low- to medium-power applications.
2. Structural Components
A typical brushed DC motor contains four fundamental parts. Understanding these elements is key to grasping the motor's operation.
2.1 Stator (Magnetic Field)
The stator creates a stationary magnetic field. In small motors, the magnetic field is usually produced by permanent magnets, while larger industrial motors may use electromagnets (field windings).
This fixed field interacts with the armature's magnetic field to generate rotational force.
2.2 Armature (Rotor)
The armature, or rotor, is the rotating part that carries the current. It consists of a laminated iron core with copper windings. When current flows through these windings, the armature becomes an electromagnet whose polarity can be reversed to maintain continuous rotation.
2.3 Commutator
The commutator is a segmented copper ring connected to the armature windings.
Its role is to switch the direction of current in the armature at precisely the right moment so that the torque always acts in a single rotational direction.
2.4 Carbon Brushes
Carbon brushes maintain sliding electrical contact between the stationary power supply and the rotating commutator.
They transfer current to the armature windings and also allow the commutator to reverse current without complex electronics.
3. Working Principle of a Brushed DC Motor
The operation of a brushed DC motor is based on Lorentz force, the fundamental principle that a current-carrying conductor experiences a force when placed in a magnetic field.
3.1 Current Flow and Magnetic Interaction
When a DC voltage is applied, current flows through the brushes and commutator into the armature windings.
The interaction between the armature's magnetic field and the stator's fixed field generates a force on the rotor conductors.
3.2 Torque Generation
The force on the conductors creates a rotational torque on the armature.
Because the commutator segments are aligned with the armature coils, the direction of current is reversed each time the rotor crosses the neutral zone, ensuring continuous rotation in one direction.
3.3 Commutation
As the armature rotates, different segments of the commutator make contact with the brushes.
The commutator automatically switches the current direction so that the armature poles are always attracted and repelled in a way that maintains motion.
This self-commutating mechanism allows the motor to produce a steady torque output with only a simple DC power supply.
4. Key Features and Performance Characteristics
Brushed DC motors offer a unique set of advantages and limitations that determine their suitability for various applications.
4.1 Advantages
Simple drive requirements - Operates directly from a DC source or basic PWM controller.
High starting torque - Excellent for loads requiring instant acceleration.
Linear speed-torque relationship - Easy to control speed by adjusting voltage.
Low initial cost - Manufacturing process is mature and economical.
4.2 Limitations
Brush wear and maintenance - Carbon brushes gradually wear out, requiring periodic replacement.
Electrical noise (EMI) - Sparking at the commutator can generate electromagnetic interference.
Lower efficiency - Friction losses and brush contact resistance reduce overall efficiency compared to BLDC motors.
Limited lifespan - Mechanical contact surfaces limit operational life.
4.3 Typical Specifications
Key parameters to consider include:
Rated Voltage and Current - Determines power supply requirements.
No-Load Speed - Speed when running without load.
Stall Torque - Maximum torque before rotation stops.
Efficiency - Ratio of mechanical output to electrical input.
Operating Temperature - Safe thermal range for continuous use.
5. Drive Circuit for Brushed DC Motors
One of the reasons brushed DC motors remain popular is their straightforward drive circuitry.
Depending on the application, control can be as simple as a switch or as sophisticated as a PWM (Pulse-Width Modulation) speed controller.
5.1 Basic On/Off Control
The simplest drive method uses a single-pole switch or relay to apply DC power.
This setup is common in toys, small fans, or other devices where constant speed is acceptable.
5.2 Direction Control
To reverse rotation, a brushed motor requires a circuit that can swap the polarity of the applied voltage.
The most common solution is an H-bridge circuit, which uses four MOSFETs or transistors arranged in a bridge configuration.
By switching pairs of transistors, the voltage polarity across the motor terminals can be reversed, allowing clockwise or counterclockwise rotation.
5.3 Speed Control with PWM
For variable speed, designers use Pulse-Width Modulation (PWM).
A microcontroller or dedicated PWM IC rapidly switches the supply voltage on and off, adjusting the duty cycle to control the average voltage and therefore the motor speed.
PWM provides:
- Efficient speed regulation without wasting power in resistors.
- Stable torque output at different speeds.
- Compatibility with low-cost microcontrollers (Arduino, STM32, Raspberry Pi).
5.4 Protection Features
A robust drive circuit often includes:
- Current limiting to prevent motor burnout during stall conditions.
- Flyback diodes across the motor terminals to suppress voltage spikes caused by inductive kickback.
- Thermal sensors to shut down the motor in case of overheating.
6. Applications of Brushed DC Motors
Brushed DC motors continue to dominate in many sectors due to their balance of cost, performance, and simplicity.
- Power Tools - Drills, saws, grinders benefit from high starting torque.
- Automotive - Door locks, power seats, windshield wipers.
- Household Appliances - Hair dryers, blenders, vacuum cleaners.
- Medical Equipment - Portable pumps and low-cost diagnostic devices.
- Hobby and Educational Projects - Robotics kits, model airplanes, DIY electronics.
For applications requiring precise speed control, low noise, and maintenance-free operation, BLDC motors are increasingly preferred.
However, when initial cost and ease of integration are top priorities, brushed DC motors remain a compelling choice.
7. Maintenance and Longevity Tips
Because brushes and commutators wear with use, regular maintenance can extend the motor's life:
- Brush Inspection - Replace brushes when they are worn to one-third of their original length.
- Commutator Cleaning - Remove carbon buildup with a soft abrasive or specialized cleaning solution.
- Bearing Lubrication - Periodically lubricate motor bearings if they are not sealed.
- Load Management - Avoid frequent stalling or overloading, which accelerates wear.
Following these practices can significantly increase operational lifespan and maintain performance.
8. Brushed vs. Brushless DC Motors
For many readers, a natural question arises: Why choose brushed motors when brushless technology exists?
The answer depends on application requirements.
Feature Brushed DC Motor Brushless DC Motor Control Complexity Simple Requires electronic controller Cost Lower Higher Maintenance Brushes need replacement Virtually maintenance-free Efficiency Moderate High Noise Higher due to brush contact Quiet operation Lifetime Limited by brush wear Longer lifespan In short, brushed DC motors excel in low-cost, low-complexity applications, while BLDC motors dominate where efficiency and longevity are critical.
9. Conclusion
Brushed DC motors remain an indispensable technology in countless consumer and industrial products.
Their simple structure, high starting torque, and easy controllability make them ideal for designers seeking a cost-effective motion solution.
By understanding the working principle, key features, and drive circuit options, engineers and hobbyists can confidently integrate these motors into projects ranging from household appliances to industrial automation.
As energy efficiency standards tighten and brushless technology becomes more affordable, the role of brushed motors may gradually shrink.
However, their unique combination of simplicity and performance ensures that brushed DC motors will continue to power everyday devices for many years to come.
