Carbon brush benefits for a dc motor

In dc motors, the carbon brush makes sure the commutation process remains free from sparks and helps conduct electric current between the moving parts of the motor.

By David Manney, L&S Electric May 19, 2017

A dc motor has several components, and each serves an important role in ensuring its proper function and efficient performance. One of these is the carbon brush, which plays a critical role.

Carbon brush basics

In dc motors, the carbon brush makes sure the commutation process remains free from sparks. This contact is a sliding contact capable of transmitting electric current from static to the rotating part of a generator or electric motor. A single or several carbon blocks composes a brush. The brush may also include one or more terminals or shunts.

These components conduct electric current between the moving parts of the motor, including stationary wires. Since the brushes perform such a crucial task, carbon brushes are vulnerable parts that tend to wear out over time.

Overuse leads to worn out carbon brushes, which is the main limitation of this type of motor. The continued need for brushes is a serious issue considering the wide availability of carbon brushes in case there is a need to have these replaced.

Although a carbon brush is susceptible to wear, these components are quite dependable. In fact, with proper care, usage, and maintenance, you can prolong the lifespan of carbon brushes. The better the condition of the brushes, the better the performance and efficiency of the dc motor.

Functions of a carbon brush

A carbon brush is a critical part of a dc motor, which relies on the brush for the transmission of electrical current coming from the machine’s rotating part. The brush is also responsible for changing the course of current in the conductors during the rotation process. The carbon brush also ensures the commutation of the current’s direction several times per rotation of the machine.

Aside from these functions, the carbon brush keeps the surface of the slip ring, or the commutator, clean. Since these brushes have a protective carbon film, it ensures a close contact as the machine operates. Thus, this prevents the motor, or commutator, from wearing out. This barrier is why the commutator maintains its smoothness and optimal condition.

Carbon is the best material for these brushes. Carbon contains all the electrical, physical, and mechanical properties suitable for protecting the motor from damages.

Main aspects of a carbon brush

Track certain sensitive areas that contact carbon brushes to ensure the proper condition of a carbon brush. Rings with a high peripheral speed tend to have a helical groove that promotes the stability of the brush.

Chamfer the edges to make sure the carbon brush does not wear out.The same holds true with commutators. Rectify any abnormality at the surface to prevent brush damages while prolonging its lifespan.

Immediately address any issues with vibrations due to poor alignment, defective running, or improper balance. These conditions prevent good contact between the commutator and the carbon brush. If you ignore these issues, problems, such as vibration, lead to severe deterioration of both the brush and the brush holder.

It may be necessary to make sure the faces of the brushes have anti-dust grooves. These grooves further promote their optimal condition and performance. Use brushes with the right length, so they adapt to the constant amount of pressure.

The carbon brush needs proper support throughout an adequate length. The brushes also need a specific clearance to avoid wedging. The International Electrotechnical Committee (IEC) has defined that necessary clearance for different brush sizes. This determination prevents issues such as hammering or wedging.

Properly align the brush holders and schedule regular cleaning upon inspection to prevent damages to the brushes over time.

David Manney is a marketing administrator at L&S Electric. This article originally appeared on L&S Electric Watts New Blog. L&S Electric is a CFE Media content partner.

Original content can be found at