Why Do DC Motors Have Brushes?

Why Do DC Motors Have Brushes?

Why Do DC Motors Have Brushes?

There are several queries that brought about the need to finally address this issue. It is not just important to professionals and students, other individuals with very little technical expertise also desire to know why DC motors have brushes. This article is not just a paragraph that provides a reply to your question, rather, it reinforces the main concepts of a brushed DC motor, helping you to see why DC motors have brushes.

Let’s start with the definition of a brushed DC motor.

What is a Brushed DC Motor?

We can define a brushed DC motor as a motor with internal commutation that is designed to be powered by a direct current source. A typical motor comprises the armature, the commutator, a battery (or a DC source), the brushes, the axle, and a magnet. There are 3 broad classifications of a brushed DC motor and they are discussed below.

Structure of a Brushed DC motor

Structure of a Brushed DC motor

Wound stators

There are four different formats of the wound stator DC motor; the separately excited wound stator, shunt-wound DC motor, shunt-wound DC motor, and the compound-wound motor. In the case of the series-wound motor, both coils (the field winding and the armature winding) are electrically connected in series.

For the shunt wound motor, just like the name implies, the armature and the field are connected in parallel. On the other hand, the separately excited motor has the field coils supplied from an external source. A typical example of the source is a motor-generator. This means that changes in the armature current do not affect that in the field current.

Permanent-magnet motors

The usual DC, excited, synchronous motors are ideal for certain applications (for example, in DC traction motors). However, permanent-magnet motors are becoming more predominant in other applications where a fraction of horsepower is required. This works particularly well because these motors are lightweight, more compact, and they have increased efficiency.

Initially, most dc motors used for industrial and commercial purposes were wound field motors, and the permanent magnet was only applicable to small motors. However, advancement in technology has engendered high-intensity magnets that support high-power magnets.

Axial field motors

Even though the usual direction of the field is in the radial direction; away from the axis of the motor, new designs with the field along the axis of the motor have emerged. This way, the rotor cuts the field lines as it rotates and this brings about stronger magnetic fields.

Difference Between Brushed and Brushless DC Motors?

A brushless DC motor uses a permanent magnet as its external rotor and there are three phases of coils surrounding it. A specialized sensor is also placed in the setup to track the position of the rotor and as it is being tracked, the reference signals are being sent to a controller.

A brushed motor, on the other hand, has a configuration of wound wire coils, carrying out the duties of a two-pole electromagnet. The direction of the current is controlled by the commutator and this ensures the flow through the armature.

Brushed and Brushless DC motors

Brushed and Brushless DC motors

Advantages of Brushed DC Motors

So why should you consider brushed DC motors?

  • They are cheaper to construct in general
  • They can be rebuilt and this extends the lifespan
  • The controller is simple and easy to use
  • A controller is not even needed if the application requires a fixed speed
  • It is ideal for extreme operating environments

Advantages of Brushless DC Motors

As alluring as the brushed DC motors appear, there are also compelling arguments for the brushless motor.

  • The absence of brushes means that it is easier to maintain
  • Can operate at any speed with rated load
  • Has a very high efficiency and very high output power
  • The speed range and noise generation qualities are superb.

Conclusion- Why Do Brushed DC Motors Have Brushes?

In summary, the brushes carry the current to the armature (the rotating part of the motor). They also work with the commutator to switch the current to ensure that it is in sync with the proper winding of the armature in the course of the rotation. This is in a bid to create the correct magnetic field and ensure that the motor runs.

Now that you know what a brushed and brushless motor is, making the right choice when it comes to selecting the right motor for specific applications is inevitable. However, to be sure that you’re on track and that you’re not making any costly mistake, feel free to contact any of our professional staffs here. We are happy to offer our help.

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