While it is true that the engines brushless DC power tools have existed for more than half a century, in the last 5 or 6 years they have starred in a revolution in the field of cordless power tools, to the point that there is no longer recognized manufacturer that does not offer the public its range of tools brushless.
One might wonder, then, what is the cause of the ruckus created by the tools current that incorporate a motor brushlessi.e. an engine no coals or brushless.
Or, in other words, for what reason is a technology that for decades was used almost exclusively in tools highly specialized precision tools today is practically the standard for cordless tools As diverse as drills, jig saws, rotary hammers, blowers, impact wrenches or lawn mowers?
The short answer
Beyond the engineering involved in brushless and brushless motorsthe answer to the above question is simple. In general, electric tools brushless motor They provide higher performance, basically because unlike brushed tools, the motor adjusts according to the task to be carried out. This represents a breakthrough when it comes to managing battery life, increasing the range and performance of cordless power tools.
On the other hand, the fact of lacking brushes means a motor that does not experience the voltage drop or friction that occurs with a standard motor. This implies: a) fewer parts subject to wear, which increases engine life and overall performance, and b) less energy loss in friction and heat, so that energy savings are invested to create greater torque.
All these advantages are summarized, then, in tools what are you offering:
- Higher RPM
- Longer battery life
- Less heat generated
- Increased durability
- Higher power
- Smaller and compact size
- Lower weight
- Quieter operation
Brushless and brushless motor technology
Addressing the details about the construction and the operation of the engines with and brushless It is beyond the scope of this note, so we are only going to treat it superficially and for illustrative purposes.
Technically speaking, both types of engines apply a similar operating principle, which is as follows. When the motor windings are energized, a temporary magnetic field is created that is repelled or attracted by the permanent magnets. The force produced is converted into shaft rotation, which drives the motor. While the shaft is rotating, the electric current is directed towards different winding groups, thus maintaining the electromotive attraction and repulsion that forces the rotor to rotate continuously.
This is the general idea. Now let’s dig a little deeper, specifically remembering how the electric tools traditional, that is, those with brushes.
In addition to the brushes, a standard DC motor has other components shown in this figure:
The armoralso known as rotoris a rotating set of coils (winding) which acts as an electromagnet with two poles. The brushes They are generally made of copper, silver or graphite and are used to convert electricity into motion. They make contact with a mechanical rotary switch called switch and they deliver an electric current. When current passes through the armature windings, a magnetic field is created, which interacts with the permanent magnets (north and south) located on the outside of the engine called stator and produce the rotation of the motor shaft.
The following figure shows an actual brushed motor and the function of its key parts.
Now let’s see how a brushless motorwhose scheme shows the next figure.
As the name implies, these motors do not have brushes or commutator. The position of the permanent magnets and the copper windings that move the armature is reversed with respect to the previous case: the windings are located on the stator, are fixed and surround the shaft, while the permanent magnets are mounted on the motor shaft in armor. This unique design totally eliminates the need for brushes, and in the absence of this, a small circuit board coordinates the power supply to the windings.
So, simply put, the main difference between a brushless motor and a brush motor is that instead of stationary magnets and rotating windings (typical brush motor design), a brushless motor has stationary windings and a rotating magnet. The main benefit is that a brushless motor is frictionless, reducing heat and increasing overall efficiency.
In addition, since the electronic system communicates directly with the stationary windings, the tool can be adapted according to the task, and that is why manufacturers market these types of devices as tools “Smart.”
To understand this concept of “intelligence”, imagine, for example, that we use a screwdriver / screwdriver to drive screws into a soft material, such as plastic. Since the electric current is constantly controlled by the electronic circuit according to the rotation of the motor, a tool provided with brushless motor detect the lack of material resistance more easily than a brushed motor and therefore only draws the little current it needs from the battery. If we later change the material for a harder one such as mahogany, for example, the brushless motor will perceive the greater resistance offered by the material and will then demand more current from the battery. In contrast, a brushed motor always draws the maximum amount of current when used, regardless of the type of material involved, which directly impacts battery life.
Pros and cons
Of course, not everything is perfect. Both one technology and the other present their advantages and disadvantages when applied to motors for cordless power tools.
The tools with traditional technology, so to speak, they are provided with brushed motors and are cheaper, the motor control is very simple and does not involve great expense, and they can operate in extreme environments (for example, hot, cold or very humid ) due to its shortage of electronic and electrical devices. The replacement of the brushes is necessary with a frequency that will depend on the use, but will at least guarantee a long service life of the tool. However, on the other hand, these motors have poor heat dissipation due to the internal armature design, and the typical problems associated with brushes, such as friction and electric arc generation, cause electromagnetic interference and decrease not only the speed range. , but also the utility of torque at high speeds.
For their part, the new brushless tools with brushless motor they have better heat dissipation because the windings are connected to the housing; These improved thermal characteristics also allow for the reduction of the size of the tools. The lack of brushes guarantees less maintenance, as well as a greater speed range, since there are precisely no mechanical limitations imposed by the brush / commutator system. Electrical noise is minimal, efficiency is high, and operation is guaranteed at all speeds with rated load. However, the introduction of an electronic circuit based on Hall-effect position sensors significantly increases the production costs of these motors and adds complexity to their control, in addition to imposing limitations on their use in extreme conditions.
To visualize it graphically, the following figure presents a comparison between motors with and without brushes that summarizes the concepts that we have just exposed.
Which tool is best with or without brushes?
It is clear that the technology used in brushless power tools provides superior performance to brushed tools. Brush motors operate at an efficiency of about 75 to 80%, which means that about three-quarters of the total power used by the motor is converted into rotational force and the rest is lost as heat. The brushless motorson the other hand, are typically 85 to 90% efficient. However, the cost of these motors is 30% higher than that of conventional brushed motors.
As we expressed before, since the brushes and the switches are in constant contact with the shaft, wear out faster with heavy use. The brushless motors They do not exhibit friction or voltage drop, helping to increase engine life and provide better overall performance. In addition, this improves battery life and operating time, and greatly reduces maintenance of the tool.
Therefore, if we are professionals who make daily and / or extensive use of cordless toolswe will probably have already opted for the brushless models, or if not, we will be considering the change. For the DIY enthusiast or home user, who occasionally uses a drill or saw for an occasional job, the extra money he will need to spend on a brushless tool it could probably be used for something else. However, if we’re thinking of making DIY a regular chore, brushless power tools might well be worth the investment in terms of life, power, and reliability.
One thing is certain, however, and that is that the drive toward cordless tools Brushless is already given and this will surely bring about a reduction in costs. The trend of many manufacturers for years to come, for brushed motors to gradually disappear from the cordless tools in order to clear the way for technology brushless does not give the pattern of it.