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Brushless DC Motor: What it is and How does it works?  

What is a brushless dc motor?

Brushless DC motor is an electric motor powered by a direct current (DC) electric supply and is commutated electronically instead of mechanical commutation like in a conventional DC motor.

Oftentimes, they are interchangeably referred to as BLDC. In addition, as suggestive of their name, brushless DC motor is an electric motor that does not engage the use of brushes in its mechanism or mode of operation.


What are the advantages of brushless DC motor

Brushless DC motor offers the following major advantages:

1. Brushless DC motors have high efficiency as compared to brushed DC motors.

2. There is no problem of sparking in the brushless DC motors due to the absence of carbon brushes and a commutator.

3. They have relatively quiet operation. That account for the reason BLDC motors produce less noise while operating.

4. Brushless DC motors can operate at high-speed under any operating conditions.

5. In the case of brushless DC motors, the acceleration and deceleration are easy due to low rotor inertia.

6. Brushless DC motors are more reliable.

7. Brushless DC motors can produce high torques over a wide range of speeds.


What are the disadvantages of brushless DC motor?

Brushless DC also has a few disadvantages listed below:

1. Brushless DC motors are more expensive than brushed DC motors.

2. We cannot supply uncontrolled high power to BLDC motors because it could damage the magnets and insulation in the motor.


How does brushless DC motor works?

Like any other motor, a brushless DC motor also consists of two main parts: stator and rotor. The stator of the BLDC motor carries stator winding distributed around the periphery of the stator.

The rotor has permanent magnets, where, the number of magnetic pole pairs can vary from 2 to 8 depending on the application and requirement. It also consists of a hall-effect sensor to provide the information to synchronize the stator excitation with the rotor position.

When the stator winding is energized, it becomes an electromagnet and produces a uniform magnetic field in the air gap. Since the input supply is DC, thus it needs to be converted into AC. This conversion is performed by using an electronic commutator (controller).

Now, the magnetic field of the stator and that of the rotor interact with each other to rotate the rotor. Here, the hall-effect sensor provides feedback about the shaft position to the electronic controller unit. Depending on the signal received from the sensor, the controller decides on a specific coil to energize.


1. Brushless motor working principle

In its operating principle, brushless motor has to turn.

As their name implies, brushless DC motors do not use brushes. With brushed motors, the brushes deliver current through the commutator into the coils on the rotor. So how does a brushless motor pass current to the rotor coils?

It doesn’t—because the coils are not located on the rotor. Instead, the rotor is a permanent magnet; the coils do not rotate, but are instead fixed in place on the stator. Because the coils do not move, there is no need for brushes and a commutator.

Brushless Motors

(Explaining the principle by the picture: Since the rotor is a permanent magnet, it needs no current, eliminating the need for brushes and commutator. Current to the fixed coils is controlled from the outside..)

With the brushed motor, rotation is achieved by controlling the magnetic fields generated by the coils on the rotor, while the magnetic field generated by the stationary magnets remains fixed. To change the rotation speed, you change the voltage for the coils.

With a BLDC motor, it is the permanent magnet that rotates; rotation is achieved by changing the direction of the magnetic fields generated by the surrounding stationary coils. To control the rotation, you adjust the magnitude and direction of the current into these coils.


2. Types of brushless DC motor

According to its design, brushless DC motors are classified into the following two types namely.

  • Outer Rotor Brushless DC Motor
  • Inner Rotor Brushless DC Motor

Types of Motors

3. Outer rotor brushless DC motor vs inner rotor brushless DC motor

The main difference between inner rotor and outer rotor brushless DC motors lies in the basic design. All brushed or brushless motors use magnets to turn.

The role of the stator is to provide a charge that will repel or attract the magnets and make the motor spin. The rotor contains those magnets and does the spinning.

On an inner rotor design, the stator is on the outside and the rotor is on the inside. On an outer rotor brushless motor, they flip.

Let’s say you have one of each type of motor with identical power outputs and overall diameters. How to do they look compared to each other?

Comparing the inner rotor brushless motor with outer rotor brushless motor, you find both have the same magnetic surface area. Since the inner rotor design has the magnets against the inside, they’re on a smaller diameter – they will need to be longer.

The opposite is the case on an outer rotor brushless motor. Attaching to a wider diameter means you can shorten the overall motor length. Also, you get a natural weight reduction.


Brushless motor vs brushed motor differences?

Durability and Sound proof: Brushless DC motors offer high durability and low electric noise generation, thanks to the absence of brushes. But in brushed motors, the brushes and commutator wear down as a result of continuous moving contact, and also produce sparks where contact is made.

Electrical noise, in particular, is the result of the strong sparks that tend to occur at the areas where the brushes pass over the gaps in the commutator. This is why BLDC motors are often considered preferable in applications where it is important to avoid electrical noise.

Method of Operation: Brushed motors are mechanically driven and brushless are electronically driven.

Mechanically driven:(brushed motors), the stator (stationary part) contains permanent magnets while the rotor (moving part) contains electromagnets. Carbon brushes in physical contact with the commutator in the rotor transfer the electric voltage to it.

This voltage creates an electromagnetic field in the rotor. By continually flipping the polarity of the magnetic pull via the commutator, spinning motion is achieved.

Electronically driven: (brushless motors), flipping occurs. The rotor contains the permanent magnets and the stator creates the electromagnetic field. Instead of brushes, an electronic controller creates a three-phase variable current that powers the motor’s coils in succession. This forms a rotating magnetic field in the stator that powers the rotor’s magnets and creates the spinning motio

Efficiency: Efficiency of brushless DC motor is higher than that of Brushed DC motor, as these motors can control continuously at maximum rotational force (torque). Brushed motors, in contrast, reach maximum torque at only certain points in the rotation.

If a brushed DC motor will deliver the same torque as a brushless DC motor, it would need to use larger magnets. This is why even small Brushless DC motors can deliver considerable power.

Longer lifespan: Brushless motors have fewer moving parts compared to brushed motors, leading to reduced wear and tear and a longer lifespan.

Reduced maintenance: Brushless motors have no brushes to wear out and replace, resulting in reduced maintenance requirements. A typical brushless dc motor diagram

Brushless Motors


What are the applications of brushless DC motor?

We have discussed about the advantages of brushless DC motor above. These unique features set it apart as the reason why brushless DC motors are often used in modern devices where low noise and low heat are required, especially in devices that run continuously.

This may include washing machines, air conditioners and other consumer electronics. They may even be the main power source for service robots, which will require very careful control of force for safety reasons.

They are also employed in coupling and assembly of many modern household appliances such as fans, pumps, blowers, etc

These are used in computer hard disc drives, CD or DVD drives, etc.

Brushless DC motors are also used in automotive such as in power steering and many other electric vehicles.

They are used in CNC machine tools, belt drive systems, and in many other industrial processes

Click to learn: Application areas of coreless DC motors


Frequently ask questions (FAQ)

1. What are disadvantages of brushless DC motor?

High cost: Brushless DC motors are typically more expensive than brushed DC motors due to the complex electronic controls required for operation.

Complex maintenance: Brushless motors require specialized knowledge and equipment for repair and maintenance, making them less accessible to the average user.

Higher power requirements for controller: Brushless motors require an electronic controller that consumes additional power, reducing overall efficiency.

Electromagnetic compatibility issues: Brushless motors can generate electromagnetic interference, which may impact other electronic devices in close proximity.

Limited speed range compared to brushed motors: Brushless motors may have a limited speed range compared to brushed motors, making them less suitable for some applications. Brushless motors may require cooling to prevent overheating during high-power operation, adding complexity and cost to the overall system.

More sensitive to voltage fluctuations: Brushless motors are more sensitive to voltage fluctuations compared to brushed motors, which may impact performance and lifespan.

It requires advanced electronic control which can increase overall cost and setup complexity


2. How many years do brushless motors last?

Brushless DC motor can sustain 10,000 runtime hours.

However, there are certain conditions to meet because the lifespan of a brushless DC motor depends on a number of factors, which include the quality of the motor, the operating conditions, operator’s handling and how frequently the motor is used.

The long lifespan of a brushless motor makes it a great choice for many applications. However, it’s important to note that brushless DC motors are not maintenance-free. They still require occasional cleaning and inspection to ensure optimal performance.


3. Why do brushless motors go bad?

brushless DC motor.

Although estimated running time can last as long as 10,000 hours, that is around 416 days, operator errors might lead to a decreased lifespan. There are many factors why a brushless DC motor may go bad or fails after only a short time. Some of the factors are:

Water: The most common reason for early failure of a brushless motor is water or dust contamination, which causes corrosion and eventually leads to bearing failure. Balance issues with bearing load also impact bearing life.

Operating Conditions: In addition to the quality of the motor, the operating conditions also play a role in determining the lifespan of a brushless motor. For instance, if the motor is constantly operated at high speeds, it will experience more wear and tear than if it is operated at lower speeds.

As a result, the lifespan of the motor will be reduced. In addition, sharp stop-and-start cycles can also reduce the lifespan of a brushless motor. These stop-and-start cycles put stress on the motor, and can eventually lead to failure.

Frequency of Use: Another factor that determines the lifespan of a brushless motor is how often it is used. If the motor is used frequently, it will experience more wear and excessive heat. Although they are made to last tens of thousands of hours or more than a year, frequent use can reduce the lifespan of the motor.

External Factors: External factors, such as vibration and shock, can also impact the lifespan of a brushless motor. These factors can cause wear and tear on the motor, and eventually lead to failure. Debris and dust also pose a risk to the motor, as they can cause corrosion and other damage.

Improper Installation: In some cases, brushless motors fail because they were not installed properly. For instance, if the motor is not mounted correctly, it will be subjected to vibration and stress. This can lead to premature failure.

In addition, if the wires are not connected properly, the motor will not operate correctly and might eventually fail. It’s always best to follow the manufacturer’s guidelines and recommendations when installing a new brushed DC motor.

Not Following Manufacturer Recommendations:Not following the manufacturer’s recommendations is one of the most common reasons why brushless motors will go bad. For instance, if the motor is not properly lubricated or cooled, it will experience excessive wear and tear.

In addition, if the motor is operated outside of its recommended operating conditions, it will likely go bad prematurely. While brushless DC motors are a favorite due to their high torque ability, using more torque or higher RPMs than what is recommended by the manufacturer can cause the motor to fail.


4. How does brushless DC motor work without brushes?

Brushless Motors DC use permanent magnets and electronic commutation, instead of brushes and a mechanical commutator, to control the flow of current in the motor.

This design provides several benefits, including improved efficiency, longer lifespan, and reduced maintenance compared to traditional brushed DC motors.

Reading reading:How do i choose a brushless motor?


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