4 Essential Things About Electric Motor Carbon Brushes


Although they function differently, electric generators and motors have tons of similarities. They’re like the opposite sides of a penny and built using the same material, and the conjunction between these two is what differentiates one from the other. As you probably know, these mechanisms have two essential parts. One is a rotating part attached to a static magnet inside a magnetic field. It rotates because the flow of electric current into the electric rotor forces it to rotate by magnetizing it. The other part is the mechanically rotating part, which causes the electric current to flow out of the machine.

Electric motor

Of course, there are other processes before you can convert mechanical energy to electrical and electrical to mechanical. One is connecting the solder to the rotor and making them function, but you have to ensure that wires won’t get entangled while rotating. Although preventing it from intertwining seems impossible, there’s one thing that can make this happen. This is where carbon brushes become crucial. This article will discuss everything you need to know about electric motor carbon brushes, from the most basic concepts to grades and troubleshooting.

1. What Are Carbon Brushes?

A carbon brush is an essential component of an electric motor that allows electric current to flow and complete a single circuit. As mentioned earlier, it’s almost impossible to let the rotor operate without the wires getting intertwined. The best way to get this task done is to use a contact mechanism. A single circuit will be complete without soldering the rotating and the static parts to each other. The primary role of carbon brushes is accomplishing this task, preventing the entanglement of wires while static and rotating parts are in constant motion.

Wires were used to create carbon brushes, making them look like typical wire brushes. However, it seems to wear and tear easily, leaving the commutator with some run-time issues. Thus, brushes made with carbon (graphite) were born. Carbon brushes also get worn over time, especially when used routinely. The alignment will be lubricated with the additives found in graphite, so graphite brushes are suitable for operational uses.

2. When Should You Replace Carbon Brushes?

Although carbon brushes are stronger and more durable than conventional wire brushes, it doesn’t mean that they don’t get worn over time. Now the question is, how would you know if they’d worn out already?

Here are the symptoms of worn-out carbon brushes:

  • Burnt Odor: Know that you need to change your carbon brush when you smell burning. The smell is most likely due to defective carbon brushes, and the burnt smell indicates that something is falling apart inside the machine.
  • Bad Performance: If the machine ceases to function as expected, that’s the sign to check up on your carbon brush and see if it needs replacement. You may try to shake it to get things starting, but its performance may not be as good as before.
  • Power Inconsistencies: If the machine suddenly stops operating, that’s a telltale sign of worn-out carbon brushes. This only indicates that the machine no longer has brushes.
  • Sparks: Although little sparks can be a usual sight for power tools, large sparks aren’t, and that’s when you should get concerned. You must replace your carbon brushes as soon as possible once you see them coming. In addition, you may check your cooling vents to monitor the condition of the sparks and whether or not they’re worsening.

Carbon brushes

3. What Are The Types Of Carbon Brushes For Electric Motors?

Carbon brushes are categorized as follows:

Graphite brushes are made by fusing graphite with resin materials and layering them to form a brush. They have great riding qualities and excellent filming, perfect for slip rings and commutators. Their fast-filming features protect the slip rings and commutators while operating under unclean working atmospheres. Their high density and low absorption rate also reduce threading in contaminated spaces.

You can distinguish electro-graphite carbon brushes from others by their optimum density and strength. This is because of what they’re made of, resulting in excellent commutating capability and performance at low humidity and high-temperature functions. You may also coat your electro-graphite brushes to ensure good performance even under contaminated working environments.

Metal graphite brushes are typically created using fine metal powders and graphite. Metal powders are usually made of copper, but tin, lead, and silver work well in other cases, too. This grade of carbon brush is often used on low-voltage and high-density commutators. Besides, metal graphite brushes have low contact drop, making them suitable with grounding brushes.

Carbon graphite brushes are the oldest forms of carbon brushes, usually made with solid materials. However, their functions are limited to older machines with lower current densities and no longer work in today’s commutators because of their high friction, which may lead to mechanical issues.

4. How Do You Troubleshoot Carbon Brushes?

If your carbon brushes are not functioning the way they should, here are things you might need to follow to troubleshoot them and make them work at their optimum performance:

  • Check if there are unnecessary metal vibrations, overloaded machines, insufficient ventilation (being in a crowded space), or contaminated air circulation.
  • Look for any damage in the filming and commutator.
  • See if the coil poles and stators are connected correctly.
  • Check if the main coils are fully functional.
  • Test the resistance of the insulation.
  • Check the brushes using the following factors:
    • Must not be too short, cracked, and burnt, and should be fully seated.
    • Adjusted electrical neutral
    • Should move well with the holder, and should not stick and have no loose shunts and terminals
    • Must have the least amount of vibration
    • Should have equal spring pressure
    • With holders that have proper spacing

Final Words

Carbon brushes are an essential part of every electric motor. Without them, tools and machines won’t be able to function well, and wires will always get intertwined with each other, leading to grave mechanical issues. Likewise, remember that carbon brushes won’t last a lifetime. They also need replacement when they get excessively worn out, affecting the performance of your machinery. Furthermore, be sure to learn how to troubleshoot your carbon brushes so you can address minimal issues, prevent serious concerns, and have them work efficiently.


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