Motors in Power Tools: Brushed and Brushless

What a motor does in a tool

An electric motor turns electrical energy into spinning motion. In nearly every power tool, current flows through coils of wire, creating magnetic fields that push against magnets or other coils and turn a shaft. The differences between motor types come down to how the current is delivered to the right coil at the right moment.

Brushed motors

A brushed motor uses small blocks of carbon, called brushes, that press against a rotating part called the commutator. As the shaft turns, the brushes pass current into the coils in sequence, which keeps the rotor turning. It is a simple, long-established, mechanical arrangement.

Strengths:

• Simple construction, which keeps cost down.
• Straightforward control: more voltage generally means more speed.
• Easy to repair or service in many cases, since brushes are a replaceable wear item on some tools.

Drawbacks:

• The brushes rub constantly, which creates friction, heat and wear. Over time they shorten and the commutator wears.
• Contact produces sparks and electrical noise inside the tool, which is normal but a reason to keep vents clear of dust.
• Efficiency is lower than a brushless design, since some energy is lost to friction and heat.
• Brushes eventually need replacing, or the tool loses power or cuts out.

Corded tools commonly use a variant called a universal motor, which runs on alternating current and is brushed. It is compact and delivers a lot of power for its size, which is why it appears in drills, circular saws, jigsaws and sanders.

Brushless motors

In a brushless motor the arrangement is reversed. Permanent magnets sit on the rotating part, and the coils are fixed in place. Because the coils do not move, there is no need for brushes. Instead, an electronic controller switches current between the coils at the right moments, usually using sensors or by reading the motor’s own signals to know where the rotor is.

Strengths, as typically described:

• Less wear. With no brushes rubbing, there is less to wear out, so these motors often last longer in heavy use.
• Higher efficiency. Less energy is lost as friction and heat, which commonly translates into longer battery run time on cordless tools.
• Cooler running and often a more compact motor for a given output.
• Smarter control. The electronics can adjust to the load, change speed smoothly, and provide features like an electronic brake that stops the tool quickly after you release the trigger. Many of these appear in recent advances in power tool technology, and they are a big part of what companies mean by brushless motors on a box.

Drawbacks:

• Higher cost, because of the controller and magnets.
• More complex electronics, which are harder to repair at home. A failure in the controller usually means a professional repair or replacement.
• Benefits depend on the whole tool design. A brushless label does not guarantee more power by itself.

Where each design shows up

Brushless designs are especially common in cordless tools, where efficiency stretches battery life. A cordless drill or impact driver with a brushless motor can often do more work per charge than a comparable brushed model, though the exact difference varies with the tool, the task and the battery. Understanding battery amp-hours alongside the motor type gives a better idea of expected run time than either number alone.

Corded tools split between the two. Many entry-level and long-established tools use brushed universal motors, while some newer corded tools and many stationary machines differ. Large stationary tools, such as table saws, drill presses and many compressors, often use induction motors. These are a third type: AC motors with no brushes and no commutator, which are durable and relatively quiet but heavier and not designed to be as compact. They are what produce the large starting surge discussed in material on circuit overloads, and their appetite is why a stationary machine may need its own circuit.

Practical differences for a buyer

When comparing two similar tools, consider:

1. How you will use it. For occasional household tasks, a brushed motor is often adequate, and the lower price may suit the job. For frequent or demanding use, many people find the longer life and run time of brushless more worthwhile.
2. Cordless or corded. The efficiency gain matters most where you are limited by a battery. On a corded tool plugged into the wall, the efficiency gain mostly shows up as less heat and wear.
3. Duty cycle and heat. Heavy, continuous loads create heat in any motor. A tool’s duty cycle information, when provided, tells you how long it is intended to run before resting.
4. Repair and replacement. Brushes can sometimes be replaced on brushed tools. On a brushless tool, replaceable parts are fewer.
5. Speed and torque. The motor is one part of the tool. Gearing, the chuck and the controller affect tool RPM and torque, and reading the specs for the whole tool is more informative than the motor label.

Care and expectations

For brushed tools, keep vents clean, avoid overloading the motor, and replace worn brushes if the manual calls for it, with the tool unplugged or the battery removed. For brushless tools, keep vents clear and avoid overheating. The cost of the tool and the way you work should guide the choice more than marketing. Either design can serve a careful user well, and the differences described here are general, since individual models vary.