Brushless Motors Defined
If you’ve shopped for power tools lately you may have noticed that many manufacturers are now touting a feature known as, a brushless motor. But what exactly is a brushless motor, how does it work, and what are its benefits? To fully understand this new technology, let’s take a quick look at the existing technology: brushed motors.
In a typical electric motor, there are permanent magnets (stator) on the outside, and a spinning armature (rotor) on the inside. The rotor contains an electromagnet. When electricity passes through the electromagnet, it creates a magnetic field inside the rotor that attracts and repels the permanent magnets in the stator. However, to make the motor spin 360°, it’s necessary to change the polarity of the electromagnet, which is accomplished by a pair of brushes.
Motor brushes aren’t brushes at all, but small blocks of carbon connected to a compression spring. The brushes press against spinning electrodes attached to the rotor. As the electromagnet spins, the brushes change the magnetic polarity.
Brushed motors are reliable, relatively efficient and inexpensive to manufacture, but they have distinct limitations. First, carbon brushes eventually wear out and must be replaced. As the motor runs, the brushes are constantly breaking and then making electrical contact, which produces sparking and noise.
The friction caused by the brushes rubbing against the spinning rotor makes the motor run hotter. And brushes limit the ultimate top-end speed of the motor. For these reasons and others, all major tool manufacturers have introduced brushless motors to their line of portable power tools.
In a brushless motor, there are no brushes of any kind and the motor itself is turned inside out: the permanent magnets are moved to the rotor, and the electromagnets are connected to the stator. Then, in place of brushes, a computer, connected to high-power transistors, charges the electromagnets as the motor turns.
There are many advantages of a brushless motor including, no brushes to wear out or replace, the motor runs quieter and cooler, no electrical sparking, and—this is really amazing—runtime for cordless tools is increased up to 50% over a comparable brushed motor.
Also, because a brushless motor is electronically controlled, it delivers the precise amount of power needed for the job. For example, the motor can sense whether you’re drilling 1/8-in.-dia. hole in drywall or a 2-in.-dia. hole in a steel door, and then deliver the correct amount of torque (power). In contrast, brushed motors run at top speed regardless of the job.
At this point I’m sure you’re thinking that brushless motors are just too fabulous to be true; there must be a catch. Well, there’s no catch exactly, but brushless motors do have one slight drawback: They’re considerably more expensive to build than traditional brushed motors. However, the initial cost is often recouped through the tool’s greater efficiency and longer life. And as brushless motors become more commonplace, the cost to consumers will surely come down.
Finally there’s no obvious visible difference between a tool with a traditional brushed motor and a tool with a brushless motor. The two tools will look identical. So, be sure to
read the tool specifications and look for the word “brushless” stamped somewhere on the tool.