Your application depends on what type of DC motor you’ll choose, as it’s important to select the right motor if you want your project to be efficient. The most common mistake people are guilty of, is not knowing what motor is ideal for an application based on different parameters like torque, speed, and even cost. The focus of this blog is to differentiate between Brush and Brushless DC motors to ensure proper configuration for all applications.
What Is A DC Motor?
A DC motor is a type of electrical machine that takes electrical power through direct current and converts it into mechanical energy/motion. DC motors are utilized in powering hundreds of devices we use daily, including medical equipment. The most common types of DC motors are the brush DC and brushless DC motors, and they both have their pros and cons.
What is a Brush DC Motor?
Brush DC motors just like their name implies, have brushes that commutate the motor to spin. It’s considered one of the simplest types of DC motor. A brush DC motor is made up of four components; stator, rotor/armature, commutator, and brushes. Brush DC motors have permanent magnets positioned inside their outer body and a rotating armature inside. The armature also referred to as the rotor contains windings of insulated wire tightly wrapped around the core of a soft iron.
The windings usually form coils and these coils are connected electrically to the commutator. Brushed motors make use of mechanical commutation of the windings via brushes to switch their current. Ideally, the stator will enclose the rotor and contain the permanent magnets to create a magnetic field whose force of attraction and repulsion stimulates the rotor to keep turning. While the rotor is turning, the winding is being energized in a different sequence to ensure the rotor doesn’t rotate outside the stator field.
Brush DC motors use metallics brushes to transfer current to the coil, and while it’s true that these motors get the job done, you need to practice frequent maintenance to ensure the brushes always operate at full capacity. The brushes and commutator are the parts of a brushed DC motor susceptible to wear.
Advantages of Brushed DC Motor
- They have a high starting torque, making them perfect for applications that need to get up to speed quickly; applications such as caravan movers, electrical propulsion, steel rolling mills, and household appliances.
- When compared to brushless motors, brushed motors are inexpensive and simple.
- It’s ideal for harsh operating conditions.
Disadvantages of Brushed DC Motor
- The brushes tend to wear out, meaning it has a short lifespan.
- It’s a less effective option when compared to its brushless counterpart.
- It’s electrically noisy.
- Periodic maintenance is necessary
- Due to the internal rotor construction, there’s usually slow heat dissipation
Different Types of Brush DC Motors
There are four types of brush DC motors;
· Permanent Magnet Brush DC
This type of DC has permanent magnets stationed in the stator, meaning you’ll not need an external field current. They are the most common types and are very cost-efficient compared to wound stators. It’s considered the lightest and most energy-efficient type of brush DC motor, and you can use it in low-power applications of up to 2 HP. The most common application of permanent magnet brush DC is for applications that need fractional horsepower like electric slot cars, toys, and home appliances.
Also, the permanent magnet brush DC is limited by its stator field due to its torque, ensuring a good low-end torque and high-end torque. This brush DC responds quickly to changes in voltage; however, it’ll lose its magnetic properties over time, causing a decline in motor performance.
· Shunt Wound Brushed DC
The shunt wound brush DC has the field coil in parallel with the rotor, and the current in both the rotor and field coil are independent of one another. So, regardless of the load, it still operates at a fixed speed. Due to its excellent speed control, the shunt-wound brush DC is typically used in industrial and automotive applications – applications that require up to 5 HP or more.
They are considered a better alternative to permanent magnet brush DC motors because they don’t experience loss of magnetism. However, it’s a costlier option, and if the shunt current decreases to zero, there’s a possibility of motor runaway.
· Series Wound Brushed DC
The series-wound brushed DC motor has the field coil in series with the rotor; meaning the field currents become the same.
In normal operation without a load, the speed is increased as the motor current increases. But when a load is put, the motor speed will decrease, while the torque will increase to overcome the load. Series wound brushed DC usually has great slow speed, but if you take off the load, the speed will increase immediately, making it the best option for high-torque applications like cranes and winches.
· Compound Wound Brush DC
It’s the combination of both the series and shunt-wound motors, and it has the performance properties of both. The compound wound brush is perfect for industrial and automotive applications, and it’s the most expensive type of brush DC motor.
What Is A Brushless DC Motor?
A brushless DC motor is a type of electric motor that uses direct current as its power source, and of course, it doesn’t use brushes. It features coils and permanent magnets, and through a series of carefully timed energizing intervals, the permanent magnet located at the center rotates around the surrounding coils. The permanent magnet is located on the outer body, while the armature is located inside the structure. It utilizes the permanent magnet as the external rotor and uses a specialized sensor and three phases of driving coils to monitor the position of the rotor.
When an electric current is applied to the armature, the rotor spins 180 degrees, and for it to surpass 180 degrees, the electromagnet poles must flip. Unlike the brushed motor that uses a mechanical commutator and brushes, the magnetic field of the stator is rotated using electronic commutation. So, to rotate the rotor to 360 degrees, a digital controller is used to charge the electromagnets in the stator. Due to its high speed and high efficiency, brushless motors are mostly used in computers, and handheld power tools.
Advantages of Brushless DC Motor
- Brushless motors have no brushes, meaning less maintenance and a long lifespan.
- It’s a more efficient option than the brushed DC motors.
- Also, because of the absence of brushes, they run quietly and smoothly.
- Brushless DC motors can produce different power outputs and torque.
Disadvantages of Brushless DC Motor
- Brushless DC motors are expensive.
- They require a controller to enable the flow of current to the electromagnets.
- They are complex to operate, design, and troubleshoot.
- There’s the possibility of brushless motors generating electromagnetic interference that can clash with other electronic devices within the environment.
Different Types of Brushless DC Motor
The brushless DC motor has two main styles;
· Outrunner Brushless DC Motor
Outrunner DC motors have a stator winding that’s directly positioned on the inner surface of the external can. However, the electromagnets don’t cool down compared to the runner brushless DC motors, meaning it doesn’t give sufficient protection from exterior elements. Because the Outrunner dissipates heat better, it requires less maintenance than the Inrunner.
· Inrunner Brushless DC Motor
The inrunner brushless DC motor is a more efficient option than the outrunner, as it spins faster and produces lower torque. It arranges the electromagnets inside a fixed exterior housing, and the permanent magnets are positioned on the internal rotor.
Major Difference Between the Brushed DC Motor and Brushless DC Motor
Noise
The brushed DC motor generates more noise due to the arcs in its brushes, while the brushless motor is quiet.
Cost
Brushless motors are more sophisticated, hence the overall cost of producing a brushless DC motor is significantly higher than that of a brushed DC motor. Yes, indeed, brushless DC motors don’t have brushes or a commutator, still, the electronics (permanent magnets) needed are expensive.
Lifespan
The major disadvantage of a brushed DC motor is that it’s prone to wear, and needs frequent maintenance to ensure optimal performance. However, brushless motors don’t have moving contacts, hence; they aren’t prone to wear.
Applications
Brushed DC motors are used for industrial applications, medical equipment, home appliances, kid toys, and robots. Brushless DC motors are used in electric vehicles, electric bicycles, washing machines, and hybrid vehicles.
Conclusion: Brushed vs. Brushless DC Motors, Which is Best?
Remember that choosing the right DC motor depends on your application. If your application requires precise control such as in robotics and automation, your best choice is a brushless DC motor.
However, if your application is power seats and power windows, then perhaps choosing the brushed DC motors is the right choice for you.
Hopefully, you understand the differences and applications of both brushed and brushless DC motors; now you can make a more informed selection.
Related reading: DC vs. AC Motors: What the Difference Between Them
