Carbon Brushes: What Are They And How Do They Work?


Carbon Brushes

Although they serve different purposes, electrical motors and generators have a lot of things in common. They are two sides of the same coin as they are designed using similar parts—and the alignment of these parts is what distinguishes the two.

As you might already know, both these machines have two main parts. There is a rotating part suspended in a magnetic field generated by a static, permanent magnet. Electric current flows into the rotor and magnetizes it, forcing it to rotate. As for the generator, the rotation is generated mechanically, which then leads to the electric current flowing out of the device via the rotor coils.

Of course, there are a lot of fundamentals that take place before you can successfully convert mechanical energy to electrical energy and vice versa. One of them is how you can connect a cable to the rotor and make it work without intertwining the wires as it rotates. This is where carbon brushes come in handy. In this article, we are going to cover what carbon brushes are and their mode of operation.

What Are Carbon Brushes?

As earlier stated, it is almost impossible to connect the coils directly to the rotor and let it operate without intertwining your cables. A better way would be to use a non-permanent contact mechanism. In other words, the electric circuit will be complete without having to solder the static and rotating parts together. Carbon brushes are, therefore, designed to accomplish this idea. As you’d expect, there is a rotating and static set of brushes, and they are constantly in contact during the rotation.

The brushes on the armature (or rotor) make up what is called a commutator. These brushes are soldered to the armature coils, and they are responsible for conducting electrical currents in and out of this part. As the rotor rotates during operation, the commutator rides on another set of brushes fixed on the stationary segment of the motor. It is worth noting that both sets are made from carbon to prevent quick wear and tear. Initially, they were like standard wires and would wear out very fast.

That’s not to say carbon brushes do not wear out; they do so sparingly. One thing that has ensured higher durability is the use of lubricating additives. Nonetheless, if you run into trouble, then has carbon brushes that you can use to replace those that have worn out. In case you are not sure about anything, ask for an expert’s opinion because it could save you a lot of resources.

How Carbon Brushes Work

There are three main parameters involved in the operation of carbon brushes. The first one is the mechanical part, which features a slip ring attached to the shaft. This slip ring is what is called a commutator, and a brush is pushed to it using a spring. To ensure effective brush contact, the commutator’s surface should not be too rough, and neither should it be too smooth. Once there is enough contact between the commutator and the brush, the electrical current is transmitted from one end to the other.

It is worth noting that not the whole brush is involved in the contact process. There are small areas called contact spots that contact the slip ring’s surface. These spots should be evenly distributed to avoid damage and maintain brush balance. Highly conductive brushes seem quite efficient, but this would lead to arching at the contact surfaces. As such, brushes with high resistivity are used in both generators and motors. Another thing that would impact the efficiency of carbon brushes is the surrounding environmental factors such as humidity and corrosive gases.

Graphite Electric Brushes

Troubleshooting Carbon Brushes

Sometimes, the performance of your dual fuel generator might not meet your expectations. If you are convinced that the main culprits are the carbon brushes, then there are several ways you could do to solve the problem. For one, be sure to check whether there is any external issue interfering with the operation. Among the main factors include air supply contamination, insufficient ventilation, and machine vibration. Check the connection between stator and coil poles. If all of them are fine, you can go on and check the health of the commutating coils. Insulation and the brushes themselves also need to be inspected.

Closing Remarks

Carbon brushes are often overlooked, but they play an instrumental role in the operation of motors and generators. They ensure that electric current is effectively transmitted from the rotative coils to the desired external points or the other way round. Since they are always in contact with the moving parts, there is a need for maintenance whenever required. Some of the main causes that would lead to carbon brush malfunction include the surrounding environment, dust, and brush stability.


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