EducationHow does a brushless dc motor work - Brushless dc motor construction

How does a brushless dc motor work – Brushless dc motor construction

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Brushless DC motors are brushless DC motor usually is able to achieve an efficiency of 85-90 percent, while brushed motors generally have around 75-80 percent. The brushes eventually wear out often causing sparks that can be dangerous which can reduce the lifespan of the motor. It is a good idea to use brushless DC motors are quieter, more efficient and last a longer duration of. BLDC motors offer a variety of advantages over other kinds electrical motors.

How does a brushless dc motor work

For a better understanding of how brushless motors work, we must first recall how a brush DC motor works, as they were used for some time before brushless DC motors were available.

brushless dc motor

In this kind of motor the electric current is pushed through coils set in a permanent magnetic field. The current generates magnetic fields inside the coils. This results in the coils to move, since each coil is pulled away from a different pole, and then pulled towards an opposite side of the magnetic field. To keep the coils rotating it is necessary to continuously reverse the current, to ensure that the polarity of the coils is constantly changing which causes the coils to in “chase” other stationary poles. The power to the coils is supplied by permanent conductive brushes that come into contact with a commutator that is rotating; it is the movement of the commutator which reverses the current that flows across the coils. The commutator and the brushes are the primary components that differentiate the DC brush motor from other kinds of motors.

The picture above shows the basic idea behind the brush motor. The fixed brushes provide electric current to the commutator that is rotating. When the commutator is rotating it continuously alters the direction of current that flows through the coils reverses the polarity of coils to ensure that they remain in a clockwise direction. The commutator is able to rotate because it is connected to the rotor that the coils are installed.

Why BLDC brushless motors rotate

Like the name suggests, brushless DC motors don’t make use of brushes. Brush motors use brushes transmit current through the commutator and to the coils on the rotor. How does a brushless motor transfer energy to the coils that are on the rotor? It isn’t able to transmit since the coils aren’t placed in the rotor. The rotor acts as a permanent magnet. The coils are not rotating but are connected with the stator. Since the coils don’t move it is not necessary for brushes or an Commutator.

brushless dc motor

Advantages of brushless dc motor

A BLDC motor that has three coils in the stator would have 6 electric wires (two for each coil) that are connected to the coils. In the majority of instances three wires are internally connected and the remaining three wires sticking out of the body of the motor (as in contrast in the case of the two wires that protrude off the brushes motor as described previously). The wiring inside the BLDC motor housing is more complex than just connecting the negative and positive wires to the battery cell. We’ll take a deeper study of the workings of these motors in the next segment that we will cover in the series. Let’s close by examining the benefits from BLDC motors.

The major benefit is their efficiency, since they can run continuously at the maximum force of rotation (torque). Brush motors on the contrary, can produce maximum torque at a low rpm. In order for an electric brush motor to produce the same amount of torque that the brushless version, the model will require much bigger magnets. So, even the smallest BLDC motors will provide more power.

Another major advantage that is related to the previous one – is the ability to control. An BLDC brushless motor is controlled via feedback mechanisms that precisely give the required torque and speed. The precise control decreases the energy use as well as heat production. when the motors are powered by batteries, extends the battery’s life.

BLDC motors are also able to provide longer life span and less electrical noise , due their absence of brush. Brush motors are a great choice because the commutator and brushes wear out because of continuous contact and can also cause sparks when they come into contact. Particularly electrical noise, it is caused by sparks that are strong that typically occur in the areas where brushes go through gaps within the commutator. This is the reason BLDC motors are generally preferred in situations in which minimizing electrical noise is essential.

Disadvantages of brushless dc motor

The drawbacks of brushless devices include the possibility of demagnetizing permanent magnets, issues with controlling the amount of flux, and the high price of the converter which rises with the power level of the machine grows. Brushless motors also suffer from the drawback of magnetic torque pulsations. Although there are a lot of studies regarding BLDC motors, a small number of publications deal with the study of electromagnetic phenomena like electromagnetic field analyses, magnetic resistance analysis, and temperature effects. The analysis of torque pulsation typically is focused on the torque trailing.

Brushless dc motor applications

We’ve seen that BLDC motors have high efficiency and controllability, as well as that they are long-lasting in their duration of service. What do they work for? Due to their effectiveness and long-lasting nature They are frequently utilized in appliances that operate in continuous mode. They’ve long been utilized in washing machines as well as air conditioners as well as other electronic devices for consumers as well as, more recently they are now found in fans, and their efficiency has allowed them to drastically reduce energy consumption.

They can also be used to control vacuum machines. In one instance one instance, a change to the control program caused the speed of the motor increasing by a significant amount which is one example of superior control capabilities offered by these motors.

BLDC motors can also be used for rotating hard disk drives. their longevity ensures the reliability of the drives for extended durations of time. Additionally, their energy efficiency helps in the reduction of energy usage in a field where this is becoming increasingly crucial.

We can anticipate BLDC motors being utilized more frequently in the near future. They are likely to be employed to control service robots , small robots which provide services outside of manufacturing. It is possible to consider that stepper motors might be better suited for this kind of job in which pulses can be used to provide precise control of positioning. However, BLDC motors are more suited to control forces. In the case of the stepper motor that maintains the position of an object, such as robotic arms will require a massive and constant current. With the use of a BLDC motor all that is required is a constant current that is proportional to the force externally and this makes it possible to control the force more efficiently. BLDC motors are also able to substitute for brush DC motors on mobile carts and golf carts. Alongside a higher performances, BLDC motors can also give more precise control which can in turn prolong battery life.

BLDC brushless motors suitable for drones. Their ability to offer precision control make them ideal for multi-rotor drones in which the drone’s movement is controlled precisely by control of the rate at which each motor rotates.


Michal Pukala
Electronics and Telecommunications engineer with Electro-energetics Master degree graduation. Lightning designer experienced engineer. Currently working in IT industry.