How It Works: Electric Motors
Learn what the differences are between brushed and brushless electric motors.
Synopsis: Power tools use electric motors. In this “How It Works” article, senior editor Justin Fink describes the differences between brushed motors and a new technology, brushless motors. Both types of motor rely on a combination of magnets and electromagnets to create rotation. The design of a brushed motor requires a physical connection between two of the parts, which creates friction and a subsequent amount of wasted energy. A brushless motor has no such connection, so no energy is wasted as the motor operates. A related article appears in FHB #226 under the “Tools & Materials” department.
Sweeping changes to power-tool technology don’t come often. The last big shift was the introduction of Li-ion batteries in 2005. The next one is brushless motors.
Most major tool brands now are either entering the brushless-motor category or expanding their current brushless offerings, and all will be promoting the new option with much fanfare. As a buyer, you’ll be faced with a decision: the standard brushed-motor tools you’ve used for years, or the new wave of premium-priced brushless motor tools. An informed decision starts with an understanding of basic electric-motor technology.
Electric motors, both brushed and brushless, rely on a combination of conventional magnets and electromagnets. Every conventional magnet has two poles (north and south). Opposite poles attract each other, and like poles repel each other. Electromagnets behave the same way, but only when electricity is flowing through them. In other words, electromagnets are like a magnet with an on/off switch. To make the shaft of an electric motor spin, the electromagnet constantly switches polarity alternately pushing and pulling against the conventional magnets to create rotation. What makes a brushless motor different from a brushed motor are the position of the magnets and the way the incoming power is delivered. Here’s how it works.
In a brushed motor, the electromagnets are attached to the shaft, and the conventional magnets are permanently fixed to the motor housing. To get electricity from the battery pack to the electromagnet while still allowing it to spin, blocks of carbon known as brushes gently press against a commutator, physically bridging the gap. This physical connection creates some friction, however, which wastes energy.
In a brushless motor, the conventional magnets are attached to the shaft, and the electromagnets are permanently fixed to the motor housing. Because the electromagnets are stationary, electricity from the battery can be delivered directly, and the poles can be alternated with the help of computer circuitry. No brushes are necessary.
For more photos and details on how electric motors work, click the View PDF button below.