Questions You Should Know about brushless power tools

If you’ve ever shopped for a cordless power tool, you’ve no doubt seen advertisements touting brushless motors. So, just what is a brushless motor, and is it worth the added price?

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Brushed direct current (DC) motors are the older technology, in use since the 19th century. The first brushless DC motor didn’t come along until . Originally prohibitively expensive, brushless motor technology has finally come within reach of a DIYer’s budget.

Whether you’re shopping for a new tool or simply wondering what a brushless motor is, here are the facts, plus a checklist to see if brushless motor tools are right for you.

What Are Brushless Motors?

To understand brushless motors and their advantages, we need to briefly talk about brushed DC motors.

Both brushed and brushless motors have two primary sections: a rotor and a stator. As their names imply, the rotor rotates while the stator is static and unmoving.

The motor functions by passing a charge through a looping wire, generating a temporary magnetic field. Because magnetic fields attract and repel other magnetic fields, the rotor will turn to align with the stator’s magnetic field. As the current passes through successive wire loops, the turning accelerates, spinning the rotor faster and faster. That ultimately results in the turn of a drill or the whirl of a vacuum.

In a brushed motor the wires are wound around the rotor, while a brushless motor has its windings in the stator.

Charging the rotor coils requires a conductor to physically touch the ends of each wire in rapid succession. Those conductors are called “brushes.” In power tools they’re most often spring-loaded squares of carbon or graphite. The repeated contact with the rotor (specifically on a part called the commutator) generates friction and heat, and it’s only a matter of time before the brushes wear down to nothing.

Brushless DC motors (BLDCs) run a charge through windings positioned around the stator, rather than the rotor. Because the windings on the stator aren’t moving, they can be permanently connected to the motor, with no need for a brush to make the connection.

Brushless Motor Advantages

Brushless motors have a number of advantages over their brushed counterparts.

Lower Maintenance

Brushes eventually wear down due to friction, resulting in sparking, inefficiency and ultimately a non-functioning motor. Eliminating brushes eliminates a major point of tool maintenance.

Less Heat

In addition, the energy lost to friction is eliminated, and the friction-generated heat is no longer a concern. Some manufacturers point out that BLDCs also produce slightly less noise. While that’s true, it only applies to the motor itself — operating a brushless hammer drill is still going to be loud.

Lighter

Brushless motors can operate with smaller magnets. This results in lighter weight. That’s a huge advantage when working with a drill or other tool that might be held overhead or at an uncomfortable angle.

Efficiency

Brushless motors need more complex circuitry to properly sequence charges to the windings. But that same complexity also allows the motors to be more dynamic, responding to resistance and only drawing as much current as needed. For example, a brushless driver/drill can use less energy when drilling into plastic than into hardwood. This is why manufacturers often tout the “smart” properties of brushless tools.

Brushless Motor Disadvantages

These are the downsides to brushless motors.

Cost

The disadvantages of brushless motors all boil down to the added complexity of their design. BLDCs require a switching controller to sequence the proper charge through the stator coils. This makes them more expensive to manufacture, which is reflected in a higher initial cost.

Complexity

Added complexity also means a higher chance of failure. We weren’t able to find any studies comparing the failure rates of brushed vs. brushless power tools, but it’s generally accepted that more complex equipment is more likely to have something go wrong.

Are Brushless Motors Worth the Extra Cost?

In general, the tools that will see the biggest benefit from brushless motors are those that see long-term or continuous use.

To determine if a brushless tool is worth the investment, ask yourself the following questions:

• Will you use this tool for long stretches at a time?
• Is the size and weight of this tool important?
• Is performing maintenance or changing the brushes something you’d like to avoid?
• Do you want a cordless tool that lasts as long as possible on a single charge?
• Do you want a tool that produces less heat?

If you answered yes to several of the above questions, or if one of them is a must-have, then the extra cost for a brushless motor will likely be worth it. But if you just need an affordable tool for occasional use, make your decision on price and comfort, and don’t focus on whether it’s a brushed or brushless motor.

What the heck is a brushless motor, and why are brushless power tools better than ones with brushed motors?

While brushless motors aren’t exactly a new technology, power tool brands have only recently begun to explore their full potential in power tools. Many brands are designing their brushless tools from the ground up, and adding in other premium features to deliver more for the step up in price.

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Milwaukee’s M12 and M18 Fuel brushless tool lineups seem to be the fastest-growing, but other brands are starting to catch up with fantastic innovations of their own.

Now, towards the end of , there are brushless drills, impact drivers and wrenches, saws, rotary hammers, and oscillating tools. There’s even a brushless band saw, and another brand came out with a brushless framing nailer.

Related: Check out our latest brushless tool coverage

With new brushless tools coming out all the time, even by consumer brands such as Craftsman, you’re probably hearing brushless thrown around a lot in product descriptions and marketing, and wondering what it all means.

Here’s a quick primer into brushed motors, brushless motors, and why tools equipped with brushless motors are so darned good.

DC Brushed Motors

A basic brushed motor has an armature (rotor), commutator, brushes, axle and permanent magnets. Current is applied through the brushes, which are in physical and electrical contact with the commutator. Current then passes through the coiled armature, creating a magnetic field.

The created magnetic fields interact with those of the permanent magnets that surround the armature, causing the armature to rotate around the axle. If you apply greater current, such as when you squeeze the trigger of a cordless power tool harder, you will create stronger magnetic fields in the armature, resulting in greater interaction forces and thus faster rotation.

As you can see in the diagram, highlighted in red, the brushes are in contact with the commutator. Friction between the brushes and the commutator results in a slight drop in speed and thermal energy losses. In addition, the brushes may need to be replaced periodically as they wear out over time with use.

DC Brushless Motors

In a brushless motor, there are no brushes, and thus no physical contact that could lead to frictional energy losses. Instead of the armature being located on the rotor with permanent magnets fixed to the surrounding shell (stator), permanent magnets are located on the brushless rotor with the armature’s electromagnetic coils in fixed positions surrounding it.

In a brushed motor, the commutator reverses the current flow through the armature coils, flipping the magnetic fields so that the rotor continues to spin. In a brushless motor, an electronic control switches the phase of current through the armature windings at precise timings to accomplish the rotational response.

Brushless vs. Brushed Motors

Brushless motors are more expensive to design and manufacture, but they are typically much more efficient than brushed motors. This leads to:

• less maintenance and longer life
• more power
• longer runtime

Often, brands have a choice in how they balance a tool’s power and runtime for optimal performance. Some might lean towards making a more powerful tool, others might lean towards making one that’s longer lasting before a battery swap or recharge is needed.

Brushless motors have become powerful enough to where brands boast about their premium brushless cordless tools having “corded-like performance.”

And, combined with latest generation high capacity Li-ion battery packs (we’re now at 5.0Ah), brushless tools provide better than ever cordless runtime as well.

Brushless Cordless Power Tools

When this post was first published in early , Dewalt and Milwaukee were the first two mainstream brands to come out with brushless power tools. We predicted that other brands would follow the trend, and that brushless motors would be incorporated into other tools beyond drills and drivers.

Now, there seems to be no limit as to the types of tools that can be redesigned with brushless motors. Also, as mentioned earlier, power tool brands occasionally build other premium features into their brushless tools.

For example, Milwaukee’s M12 Fuel brushless drill has a 1/2″ chuck instead of 3/8″. Many brands’ brushless impact drivers and wrenches now offer electronic speed and torque settings that allow you to dial down the power depending on the application and fastener size.

With all the benefits of brushless power tools, it’s no wonder why they top brushless tools in many areas.

In our best cordless drills, best impact drivers, and best cordless oscillating tools recommendations, brushless tools earned highest honors.

There is a downside to brushless cordless tools – they’re pricey. They’re more expensive to design and manufacture, and so they cost more to end users. The bright side is that brands often design brushless tools with premium features and improved capabilities to help you see past the higher pricing. Kits are often bundled with the latest-and-greatest Li-ion battery packs to make them even more compelling.

Additional Considerations

A brushless vs. brushed motor comparison is not exactly as black and white as described. For example, moving the armature from the rotor to the stator also results in a decrease in mass and radial mass distribution of the rotor. In other words, the rotor of a brushless motor often has a much lower moment of inertia than that of a brushed motor. This means that a brushed motor rotor is more resistant to rotation. (Visualize a spinning ice skater with their arms reaching out vs. at their sides.)

So it’s not just about boosting efficiency by reducing brush-commutator frictional energy losses. Additional fundamental advantages of brushless motors include improved heat dissipation, flatter torque, reduced electrical noise, and greater power output.