What Is a Brushless Motor and How Does It Work?
When it comes to power tools, you have a lot of choices when it comes to motor types, and brushless DC motors are just one of the many options available. Although the brushless motor has been used in applications such as assembly-line conveyor belts and even radio-controlled cars since approximately 1962, only recently have they become all the rage in the world of power tools.
Several companies now market brushless motors in tools such as power drills and chainsaws, and many engineers will tell you that these types of motors might just be the ideal choice for many of your power tool needs.
Why is this true?
To completely answer this question, we must first define the brushless DC motor and explain how they are distinguished from their brushed motor predecessors, which are still widely in use today as well.
We will also explain exactly how the brushed DC motor works and the many advantages these types of motors offer.
What Is a Brushless Motor?
Brushless motors, also known as Brushless DC motors or BLDC motors, are synchronous electric motors that move around, or are “commutated” electronically. They use direct current (DC) powering magnets to move the rotor within the stator. In lieu of utilizing brushes and a commutator, Brushed DC motors use a step motor controller—a controller that creates a rotation that in turn converts electrical energy into mechanical energy.
History of the Brushed and Brushless Motor
History of the Brushed Motor
Before we talk about the advent of the brushless motor, let’s first take a quick look at the roots of the conventional brushed motor for comparison’s sake.
Up until the 1980s, the conventional brushed motor was the standard choice and industry standard whenever torque control or speed was a requirement. This conventional brushed motor can be traced back to the 1830s and the work of Michael Faraday, whose attempt to determine whether or not a current carrying wire could produce a circular magnetic field around it was an outstanding success.
Cheap to manufacture, the conventional brushed DC motor can range in output from just a few watts to several megawatts. Today, the major applications for the brushed DC motor are many, ranging from steel rolling mills to railway traction devices to robotics to printers.
History of the Brushless DC Motor
Once the efficiency of the conventional brushed motor was fully maximized, the door became open to explore a motor type that was even more efficient, and the result was the brushless DC motor.
Brushless DC motors, which unlike their predecessors require no physical commutator - a revolutionary difference - were first unveiled n 1962, when T.G. Wilson and P.H. Trickey introduced what they called “a DC machine with solid state commutation.”
As this motor was gradually refined and further developed over the years, it became a fashionable choice for a number of applications that require a motor, such as computer disk drives, robotics, and even aircraft. Some fifty years later, and due to their efficiency, these brushless DC motors are still used in these same devices today, as well as in a number of other applications.
In their early years, brushless motors were a great choice for the above-named applications because they eliminated brush wear, which was a big problem with their brushed counterparts. Brushes would wear down due to the intense demand the devices placed on the motor or, in the case of aircraft, due to low humidity.
Because brushless DC motors had no brushes that could wear out, they represented a great leap forward in motor technology. But as reliable as these motors were, these very early brushless DC devices were not able to generate a great deal of power.
This “power conundrum” would change in the 1980s, when permanent magnet materials became readily available. The use of permanent magnets, combined with high voltage transistors, enabled brushless DC motors to generate as much power as the old brushed DC motors, if not more.
Near the end of the 1980s, Robert E. Lordo of the POWERTEC Industrial Corporation unveiled the first large brushless DC motor, which had at least ten times the power of the earlier brushless DC motor.
Fast forward to the present day, and you’ll discover that almost every major motor manufacturer produces brushless motors capable of doing very high-powered jobs. In terms of power tools, companies such as Makita, DeWalt and Milwaukee Tools have recently released a slew of products with brushless motors, from chainsaws to impact drivers, with Makita being the first company to release a three-speed brushless impact driver back in 2009.
How Do Brushless Motors Work
As we mentioned above, the main difference between a brushed and brushless motor is that the latter requires no brushes and no commutators. Also, the locations of the magnets and windings on the two types of motors are reversed.
The magnets in brushless motors are on the conventional motor shaft and the copper windings of the armature are fixed and surround the drive shaft. Instead of relying on brushes and a commutator, a small circuit board coordinates the energy delivery to the windings.
Because the electronics on the brushless motor communicate directly with the stationary windings, the tool adjusts according to the task. For this reason, brushless motors are often marketed as “smarter” tools than their brushed predecessors.
This “intelligence” can be seen in tools like brushless power drills. When drilling through softer materials, such as Styrofoam, the brushless drill can actually sense the lack of resistance (compared to a brushed motor) and will thus pull only the energy it needs from the battery, leading to longer battery life.
Of course, if the next task is to put screws through some type of hard wood, the brushless motor will adjust and draw more current. By contrast, a drill with a brushed motor will always run at top speed regardless of the task.
Brushless motors can often be more powerful than their brushed counterparts. Because the copper windings are located on the outside of the motor configuration, there is plenty of room to make the windings larger in these types of motors. Additionally, brushless motors do not have the friction and voltage drop of their predecessors, which happens when brushes drag against the spinning commutator.
This constant physical contact leads to consistent energy loss every time the tool/motor is in use.
Simply put, the brushless motor is not only more efficient than the conventional brushed motor, but also more durable. So why, you might be asking, doesn’t every tool have a brushless motor? Well, according to M. Coulis of Milwaukee Tools:
"While the benefits of brushless technology are vast, manufacturers encounter extreme cost barriers due to the added cost of the motor and electronics that it takes to manage the motor properly. In other words, brushless motors are expensive, and are thus better suited to benefit pros who can shell out the big bucks for a tool that they're going to use every day.”
In summary, a brushless motor is very efficient, powerful and extremely durable, but their cost, at least for now, is somewhat prohibitive.
Benefits of a Brushless Motor
Before we look at the many advantages of using a brushless motor, let us first take a closer look at the DISADVANTAGES associated with conventional brushed motors.
Disadvantages of the Conventional Brushed Motor
Although the conventional brushed motor is simple and cheap to manufacture, there are several problems that make them inferior to brushless motors. Some of these include:
- Speed. The speed of the conventional brushed motor is limited due to the brushes.
- High-Maintenance. With continued use, the brushes on the conventional motor will eventually become worn out and therefore require occasional replacement and maintenance.
- Friction. The friction caused when the brushes contact other mechanical parts like the commutator can lead to voltage drain, contact wear and heat buildup, ultimately reducing the performance and durability of the motor.
- Limit on Poles. Using brushes limits the number of poles the armature can have.
- Overheating. The brushed motor is more difficult to cool since the electromagnet is at the center of the motor.
Benefits of the Brushless Motor
Due to their efficacy, amazing durability, speed of operation and smooth torque delivery, the use of brushless motors in many applications (including power tools) is on the rise.
Here are just some of the advantages of using these types of motors:
- No Brushes Means Less Heat. The lack of brushes in a brushless DC motor means there is very little friction when these motors are in use and thus the production of heat is severely reduced.
- Durable. With very low friction and smart technology, the brushless motor tends to last far longer than conventional motor types.
- Increased Power and Performance. The minimal friction, heat transfer and the lack of motor wear associated with the brushless motor (the latter being the result of almost no mechanical contact), vastly improves the power of these devices and the electrical efficiency that leads to increased performance.
- Longer Battery Life. With power-sensing technology, the battery on most brushless motors tend to last 50 % longer than that of conventional brushed motors.
- Less Noise. Less friction equals a reduced amount of sparking and electrical noise.
- Better Heat Dissipation. With brushless motors, heat dissipation is more efficient because the stators where the windings are located are connected to the case.
For these and other reasons, brushless motors are increasingly replacing brushed motors in the marketplace. Their lack of brushes and a commutator translate to better efficiency, and means there are fewer parts that can potentially wear out or break, especially when compared to conventional motors whose friction often leads to maintenance costs or the cost of a new motor. In addition, a brushless motor tends to be much more reliable, longer lasting and powerful than earlier types of motors, with a life expectancy of 10,000 hours or more.
Brushless motors can operate efficiently at speeds above 10,000 rpm in both loaded and unloaded conditions. It is also capable of operating with less noise and electromagnetic interference than a brushed motor because its internal parts are completely enclosed.
Why Should You Consider a Brushless Motor for Your Next Tool
As you can see, brushless motors offer plenty of advantages over conventional brushed motors. So why should you consider buying a tool with a brushless motor, even though it may be more expensive. Let’s take a look:
If you have only a small project that needs completing over a very short time, a cheaper brushed motor might be all you need to get the job done, and it will certainly be more cost effective. However, if you are buying a drill, chainsaw or other power tool that you plan to use daily or least often, you may want to upgrade to a cordless device with a brushless DC motor.
Construction and maintenance companies spend thousands of dollars each year to fix or replace brushed motor power tools. And although the initial cost for brushless motors may sound staggering at first glance, it is just a drop in the bucket compared to the tool maintenance and replacement tab incurred by many of these companies.
Because there is no friction caused by brushes contacting internal engine parts, the brushless motor is much quieter to run. And if you plan to use your brushed motor tool on a regular basis, this can be a huge benefit.
The smart technology employed in brushless devices like drills and chainsaws can sense the resistance or lack thereof, drawing only the power it needs for jobs that require less resistance, and leaving more power for jobs that are more demanding. This also leads to a longer battery life—about 50 percent longer than that of its brushed predecessor.
Because of all the points we outlined and discussed throughout this article, it seems clear that brushless motors are definitely here to stay, especially given their power and efficiency. However, until their components become a bit more cost effective, it will probably be a while before the technology filters down to all power tools for weekend Do-It-Yourselfers.