Motors 101: What Is a BLDC Motor?

A brushless direct current motor (BLDC) is a small but powerful type of electric motor that uses direct current as its power source. Because of their size and efficiency, BLDCs are increasing in their popularity and the number of applications they’re used for.

What is DC Power?

Electrical current is the movement of electrons through a conductor, such as a wire. There are two types of current:

• Alternating current (AC)
• Direct current (DC)

Alternating current means that the electrons periodically change direction. This is caused by an alternator or rotating magnet which alters the direction the electrons travel 60times/second. AC current originates from a generator and is suited for mass production and distribution.   Ac power can directly power certain motor types, such as ac induction motors.

Direct current means the electrons only move in one direction. DC power originates from a battery or a power supply connected to ac line power.

How Does DC Power My Motor?

In a brush dc motor, carbon “brushes” ride on a copper commutator, which is a series of axially oriented copper bars connected to a series of windings in the rotating armature.  At any one time, the windings energized are the ones that will cause an attractive force to the permanent magnets bonded to the inside of the motor housing.  This causes motor rotation without the need for any electronic control.

A BLDC motor is constructed differently.  There are no brushes and the windings are stationary.  The rotating portion (rotor) does not have any windings.  This is where the permanent magnets are mounted.  To make shaft rotate, an electronic control circuit must switch current to the appropriate windings in the correct sequence to cause rotation.  Most use a three phase winding scheme and are controlled by a three phase inverter.  This electronic circuit regulates the speed and torque of the motor by varying the frequency and magnitude of the three phase power driving the motor.

Why is a BLDC better?

Without the carbon brushes and copper commutator, the only wear items in a BLDC motor are the bearings.  This makes the BLDC motor far superior when long operating life is required.

Because the windings are stationary and in thermal contact with the outer case, heat is dissipated more easily, allowing for higher power operation in the same package size.  Also, with no brushes and commutator, the overall length is shorter.

Without the mechanical contact of the brushes, higher speeds and peak loads are practical.

Carbon brushes are a design feature from early electric motors. They are still used today as an inexpensive alternative to brushless motors.

In brushed motors, a carbon brush serves as the means to conduct electricity to the rotor. The disadvantage is that friction between the stationary brushes and moving rotor can cause wear and loss of power.

Brushless motors replace the less-durable brush design with an electronic controller. The controller controls which coils in the stator are active, making for an ever-changing magnetic pull.

BLDC motors boast a higher speed range and better torque to speed ratio. They also deliver a higher level of torque relative to their size making them ideal in applications such as power tools.

A Growing Diversity of Applications

BLDC motors have proven to be a reliable choice in numerous applications, especially in higher volume situations.

Because they are efficient, quiet and able to run continuously for long periods they are a solid choice for automation, agricultural and domestic functions. Some of the more common uses include:

• Power tools
• Garden equipment
• Scanners
• Robots
• Computers
• Material Handling / Conveyors
• Pumps
• Blowers
• Robotics
• Medical Equipment

We Know BLDC Motors

Wondering if a BLDC motor is the right choice for your application? We can help. Put our 30+ years of experience to work on your project. Call 763-383-6936  or contact us to get in touch with a friendly BLDC expert today.