Making the Right Motor Selection

When designing consumer products whether they be vacuum cleaners or other floor care products or other products such as treadmills or kitchen appliances, it is important to understand your options to be able to produce the highest quality, most competitive product. Nowadays, a motor can be seen as the heart of most electrically powered consumer products. Whether it be household vacuums or fans, the question of “what motor should I use?” will eventually be asked. With respect to consumer products motors, the first decision is often ‘brush vs brushless’ motors, which is right for this application?

With so many options for motors, deciding on the one with the correct specifications can be difficult. A lower-quality motor may cut down the initial product cost, but could lead to premature failures or warranty issues in the future along with customer complaints and a diminished brand. An over-specified motor can prevent under delivering on product quality, but drive up initial cost to the point in which your product is no longer cost-competitive.

Now you have a learning curve to climb. In order to produce the best, most competitive products, the basics of motors must be understood. Here we discuss one of the most basic electric motor decisions, brush vs. brushless motors.

What are brushes?

Brushes are a major component in a brushed motor used to produce opposite polarities between the rotor and stator in order to produce a torque. An electric motor brush is composed of low-friction, conductive materials such as graphite. The motor brush rests on a rotary electrical switch, or commutator, and delivers current from a power source to the armature, allowing the armature to act as an electromagnet.

Example – Brush Motor for Consumer Products Applications

How does a brushed motor work?

A brushed motor consists of a commutator, brushes, wound wire coils called an armature positioned around the rotor, and a stationary magnet which acts as the stator and provides a constant magnetic field. Brushes are connected to a power source and rest on the commutator, allowing the current to flow between the two components. The current then flows through the commutator to the armature. When this current flows through the coils, the armature begins to behave as an electromagnet. The opposite polarity of the armature and stator forces the armature and commutator to begin to rotate. As the armature rotates, the commutator rings connect with the power source of opposite polarity, reestablishing the magnetic attraction between the armature and stator, and allowing the rotor to continue to rotate. As the armature approaches a perpendicular position to the stator’s magnetic field, the torque produced gradually decreases until the commutator switches polarity. This gradual decrease in torque results in irregular motion of the rotor. To prevent this, more coil loops are added to the configuration. This produces a more fluent motion of the rotor and a more consistent torque. Figure 1 displays the components of a basic brushed motor.

Example – Brushless Motor for Consumer Products Applications

How does a brushless motor work?

A brushless motor is constructed using a permanent magnet rotor and a stator with a coil configuration as shown in Figure 2. By applying power to the coils, they are energized and act as electromagnets. The operation of a brushless motor is dependent on the relationship of the permanent magnet and the electromagnet. Relating to Figure 2, as coil A and coil C are energized, the poles of the permanent magnet rotor are attracted and move towards the oppositely charged coil. As the permanent magnets begins to approach the opposite polarity coil, power to coil A and coil C are restricted and coil B and Coil D are energized. Thus, the process is repeated. To increase torque and power output of the motor, the previously charged coil may be energized in a way to repel the permanent magnet rotor and push it towards the next energized coil. An electronic sensor and electronic controller is used to determine the polarity and time of when each coil should be energized.

When to use a brush vs. brushless motor

Brushless motors can be seen in many more applications compared to brush motors due to several advantages. Brushless motors lack of brushes increases their lifetime and decreases the motor’s overall maintenance. Without the constant friction caused from the brushes rubbing against the commutator, damaged due to friction as well as overheating effects are eliminated. Due to the lack of friction, brushless motors also offer higher efficiencies. Brushless motors typically operate at efficiencies of 85-90%. This is substantially higher compared to a brushed motor, which typically operate at efficiencies of 75-80%. The use of an electronic controller allows a brushless motor to have a wider operating range. Brushless motors can deliver precise amounts of torque depending on the load by altering the amount of current sent through the stationary coils.

Although brushless motors contain many advantages, they come with a price. With the integration of the electronic sensor and electronic controller, the price of a brushless motor is usually much greater than a brushed motor. Brushed motors are directly wired to a DC power source and can be operated using a simple switch. This allows the cost of brushed motors to be significantly lower and in some cases this allows them to operate in much harsher environmental conditions.

Brush vs. Brushless Motors Comparison

Brushed Motor

Advantages

• Lower cost

• Higher durability

Disadvantages

• Lower efficiency

• Shorter lifespan

• Higher electrical noise

What is the right motor for my consumer product design?

In summary, both brushed and brushless motors carry their own pros and cons. Brushless motors can be applied to situations in which precision and lifetime are focused, while brushed motors are best used for minimizing cost with good durability.

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