What is a brushless motor and how does it work? We’ll answer these questions in this article.
In our modern age of electric tools and gadgets, it should come as no surprise that brushless motors are becoming more common in the products we buy. Although the brushless motor was invented in the mid 19th century, it wasn’t until 1962 that it became commercially viable.
What is a brushless motor?
Brushless motors are synchronous electric motors that move around electronically. They utilize direct current powering magnets to move the rotor within the stator. Instead of using brushes and a commutator, the motors use a step motor controller. It creates a rotation that in turn converts electrical energy into mechanical energy unlike the brushed or conventional motor.
History of the conventional brushed motor
The conventional brushed motor was the automatic choice where torque control or speed was a requirement until the 1980s. Its history can be traced back to the works of Michael Faraday in the 1830’s. His work to determine whether or not a current-carrying wire could produce a circular magnetic field around it was a success.
Other scientists such as William Sturgeon and Joseph Henry, who based the work on Faraday’s experiments led to the birth of well-established design of the brushed DC motor.
The major application of the conventional motor range from railway traction, steel rolling mills, robotics and printers.
They have a relatively wide range of output from several megawatts to a few watts such as those used in building toys.
The conventional motor is simple and cheap to manufacture but has several problems that make it inferior to the brushless motor.
- The speed of the motor is limited due to the brushes.
- The brushes will eventually become worn out and, therefore, require occasional replacement and maintenance.
- Friction caused due to mechanical contact of the brushes leads to electrical loss, contact wear and build-up of heat which reduces the performance of the motor considerably and also reduces its durability.
- Using brushes limit the number of poles the armature can have.
- The motor is harder to cool since the electromagnet is at the center of the motor.
Brushless motors are increasingly replacing brushed motors due to their superior efficiency, smooth torque delivery, high durability and their high speed of operation. Their application, in the past, has been greatly limited due to the additional cost of the complex motor controller that is necessary to operate the motor.
Brushless motors vs Brushed Motors.
The basic principle into the inner workings of both motors is essentially similar. When the motor windings are energized, it creates a temporary magnetic field that repels or attracts against permanent magnets.
The force produced is then converted into shaft rotation that makes the motor do work. While the shaft rotates, an electric current is directed towards different sets of winding, therefore, maintaining the electromotive attraction and repulsion that forces the rotor to turn continuously.
Brushless motors are more efficient in the conversion of electrical energy into mechanical energy than the brushed motors. They lack a commutator that allows for reduced maintenance and complexity as well as lower electromagnetic interference.
They can develop high torque, a good speed response and can be controlled easily with an MCU (Motor Control Unit).
They also operate in a wide speed range that allows for fine motion control and hold torque when stationary.
So, what makes brushless motors and brushed motors different?
The brushless and brushed motors mainly differ in construction.
Brushes in the brushed motors are used to deliver the current to the windings through the commutator contacts.
However, brushless motors do not require commutators. The field in the motor is switched through an amplifier that is triggered by a commutating device. An example would be an optical encoder that measure fine movements since they do not rely on motor phases.
The windings on a brushed motor are located on the rotor whereas they are located on the stator in the brushless motor. By positioning the windings on the stator or the stationary part of the motor, the need for brushes can be eliminated.
In a nutshell, the main difference between a brushless motor and a brushed motor is that instead of stationary magnets and spinning wires (brushed), a brushless motor has stationary wires and a spinning magnet. The main benefit is that a brushless motor has no friction, therefore reducing heat and increasing overall efficiency.
Common applications of the brushless motor
Brushless motors are used in the place of various types of AC motors. It reduces the power required to operate the devices significantly. It increases the devices overall efficiency. Small battery-powered devices use brushless motors to improve the drive efficiency, therefore, increasing the length of battery life.
In robotic vacuum cleaners where MCU speed control is needed the brushless motor is used. It enables bi-directional operation and provides high torque response as well as low noise.
Small household appliances tend to be produced in very high volumes. Therefore, one of the most important requirements is cost effectiveness. The brushless DC motor is therefore preferred over the brushed motor. It allows for lower prices of the devices while at the same time ensuring that the product quality is maintained.
The low weight and high output power of the brushless motor are desirable for production of hand tools such as snow blowers and chainsaws. They contain minimal parts such as the commutator, rotary parts and slip rings that contribute to increasing its weight.
The brushless motors also dominate several applications such as hard drives, pumps, fans, coffee machines, hair dryers, mixers and CD/DVD players in variable and adjustable speed applications.
Compare the Performance for Drills
Advantages of the brushless motor:
- The lack of brushes ensures that there is low friction during the operation of the motor and reduced production of heat, therefore, increasing the durability of the motor.
- The minimal heat and motor wear due to lack of mechanical contact on the motor vastly improve power transfer and electrical efficiency that leads to increased performance and power.
- The increased efficiency of the brushless motor helps to prolong battery life up to 50% or more.
- There is no sparking and the motor produces less electrical noise.
- Heat dissipation is better since the stator where the windings are located are connected to the case.
Disadvantages of the brushless motor:
The initial cost of the motor is high due to the need for commutating devices such as the encoder and a controller or drive.
Why are the brushless motors the better choice?
The brushless motor provides greater reliability and efficiency for its low weight and size as compared to the brushed motors.
Efficiency for the brushless motor is typically between 85-90% while that of the brushed motor ranges between 75-80%. The significant difference in efficiency means that more of the total power that is used by the motor is converted into a rotational force, and therefore, less energy is being lost in the form of heat.