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When to change brushes on the electric motor

Motors are an indispensable part of daily life and in various industries. Keeping them running smoothly requires regular maintenance, especially carbon brushes that are frequently used.

In this article, we’ll explore why it’s important to study carbon brushes, learn to determine when it’s best to replace your carbon brushes, identify signs that your carbon brushes are worn, and learn the best ways to maintain these important motor parts.We also introduced How Do I Know If My Brushless Motor is Bad in our previous article, we hope it will be helpful to you.

What are carbon brushes?

Carbon brushes are an important part of the electric motor. They are responsible for conducting electrical current between the stationary and rotating parts of the motor, known as the stator and rotor respectively. 

Carbon brushes consist of a carbon block or graphite composite, which is held in place by a brush holder or brush box. They are fitted into the brush holder and make contact with the rotating commutator or slip rings of the motor.

carbon brushes

How do you know if your carbon brushes need to be replaced?

Carbon brushes are key components of motors. They conduct current between the stator (stationary part) and the rotor (rotating part) of the motor. 

Carbon brushes are composed of carbon blocks or graphite composite materials and are held in place by a brush holder or brush box. They are installed in the brush holder and come into contact with the motor’s rotating commutator or slip ring.

Decreased motor performance. If you notice a decline in the motor’s performance, such as reduced speed or power, it could be an indication that the carbon brushes are worn. As the brushes wear down, they become less effective in conducting electricity, resulting in decreased motor efficiency.

Excessive sparking or electrical noise. When carbon brushes wear out, they may not make proper contact with the commutator, causing sparking or electrical noise. Excessive sparking can lead to damage to the motor or other electrical components, and noise is a clear indication that something is amiss.

Visible brush wear. It is recommended to regularly inspect the carbon brushes for any signs of wear. If the brushes are significantly worn down, with only a small amount of material remaining, replacement is necessary. Always check the brush surface for signs of chips, cracks, or damage.

Intermittent or erratic motor operation. If the motor operates erratically or intermittently, it could be due to the carbon brushes not making consistent contact with the commutator. Inconsistent contact disrupts the flow of electricity, leading to irregular motor performance.

Overheating. If the motor becomes unusually hot during operation, it could be a result of worn-out carbon brushes. Diminished brush contact can lead to increased resistance, causing the motor to overheat. Overheating not only affects motor performance but also potentially damages other motor components.

High brush spring tension. The tension of the brush springs plays a crucial role in maintaining proper contact between the carbon brushes and the commutator. If the brush springs are overly tight, it can lead to excessive wear on the brushes. Adjusting or replacing the brush springs may be necessary to prevent premature brush wear.

Maintenance schedule. Lastly, following the manufacturer’s recommended maintenance schedule is essential to ensure the longevity and optimal performance of an electric motor. Carbon brushes are typically included in these maintenance guidelines, and regular replacement may be necessary depending on the motor’s usage and operating conditions.

Keep in mind that how long carbon brushes last can change based on factors like how often the motor is used, the load it carries, and the conditions it operates under. Regular inspection and maintenance are crucial to identify the signs of wear and replace the brushes promptly to avoid motor damage or failure.

Remember, if you are unsure about the condition of your carbon brushes or feel uncomfortable replacing them yourself, it is always best to consult a professional technician or electrician. They can provide accurate assessments and perform the necessary replacements while ensuring proper motor operation.

carbon brushes

What does a worn carbon brush look like?

Carbon brushes play a pivotal role in Brushed DC Motors, as they bridge the electrical connection between the static and moving parts of the motor. Over time, these brushes can become worn out due to constant use and friction. Recognizing the signs of a worn carbon brush in these motors is crucial in determining when it’s time to replace it. Here are some indicators to look out for:

1. Reduced brush length. One of the primary visual signs of a worn carbon brush is a significant reduction in its length. As the brush wears down, it becomes shorter, resulting in reduced contact with the motor’s commutator or slip rings. When the brush becomes excessively short, its effectiveness in conducting electricity diminishes, leading to various motor performance issues.

2. Chipped or broken edges. Another noticeable indication of a worn carbon brush is the presence of chipped or broken edges. As the brush rubs against the commutator, it can develop small cracks or fractures, especially if it is exposed to excessive heat or significant mechanical stress. These damaged edges can disrupt the flow of current and cause unwanted sparks or uneven contact, compromising the motor’s efficiency and reliability.

3. Excessive sparking. When a carbon brush becomes worn, it may generate excessive sparking during motor operation. This can occur due to the irregular contact between the brush and the commutator, resulting from its diminished length or damaged edges. Excessive sparking can not only lead to motor inefficiency but also create a fire hazard if left unaddressed.

4. Carbon dust accumulation. Over time, a worn carbon brush will produce carbon dust as it wears against the commutator or slip rings. You may notice a buildup of dark, powdery residue around the brush holder or inside the motor housing. This carbon dust is a clear sign that the brushes are deteriorating and need to be replaced promptly.

5. Inconsistent motor performance. As carbon brushes wear down, the motor’s performance may become increasingly inconsistent. You may experience issues such as reduced power output, erratic motor speed, or even intermittent motor failure. These performance problems often stem from the compromised electrical contact between the brush and the commutator, highlighting the need for brush replacement.

It’s important to note that the appearance of worn carbon brushes may vary depending on the specific motor type and operating conditions. Therefore, it’s always advisable to consult the motor’s manufacturer or an experienced technician for guidance and replacement recommendations.

Remember, catching early signs of wear in carbon brushes and acting promptly is essential for the seamless operation of your electric motor, ensuring its longevity, and avoiding costly repairs.

Click to read our article: How Does a Brushed Motor Work?

Caring for Electromechanical Brushes

At the core of electric motors lies the critical role of electromechanical brushes. For the best performance and to get the most life out of these brushes, consistent and regular upkeep is essential. Here are some essential steps to help you maintain electromechanical brushes effectively:

carbon brushes

1. Inspect Regularly. Conduct regular visual inspections of the brushes to check for any signs of wear or damage. Look for worn-out bristles, excessive sparking, or uneven wear patterns. Identifying these issues early on can prevent further damage to the brushes and the motor.

2. Clean Thoroughly. Accumulation of dust, debris, or carbon particles can affect the performance of electromechanical brushes. It is crucial to clean them regularly. Start by turning off the motor and removing the brushes from their holders. Use a soft brush or compressed air to remove any loose dirt and debris. Be careful not to damage the bristles during the cleaning process.

3. Check Connections. Ensure that the connections between the brushes and the terminals are secure and clean. Loose or corroded connections can disrupt the flow of electricity, leading to poor brush performance. Clean the connections using a contact cleaner or mild solvent and tighten them securely.

4. Replace Worn-out Brushes. When the brushes have worn down significantly, it is essential to replace them promptly. Continuously running the motor with worn-out brushes can result in reduced efficiency, increased heat generation, and even motor failure. Refer to the manufacturer’s guidelines or consult a professional technician to determine the appropriate replacement brushes for your electric motor.

5. Maintain Proper Brush Pressure. The brushes should have the correct amount of pressure against the commutator or slip rings. Excessive pressure can lead to accelerated wear, while insufficient pressure can cause poor electrical contact and inefficient motor performance. Consult the motor’s manual or an expert for guidelines on adjusting the brush pressure correctly.

6. Keep the Environment Clean. Maintaining a clean environment around the motor can prevent contamination and prolong the life of electromechanical brushes. Keep the area free of dust dirt or other debris that may affect the performance of the brush. Regularly clean the motor and surrounding areas to minimize the risk of contamination.

7. Follow Manufacturer’s Recommendations. Lastly, it is crucial to follow the manufacturer’s recommendations regarding brush maintenance. They might offer precise instructions on cleaning techniques, when to replace parts, and how to lubricate. Heeding this advice ensures the motor runs at its best and sidesteps unwarranted wear and tear.

Sticking to these tips and giving your motor’s carbon brushes regular attention can extend your motor’s life and keep it humming smoothly. A routine of inspecting, cleaning, and updating old brushes can fend off surprise breakdowns and costly fixes.


In general, replacing the motor carbon brushes can not only keep the motor running smoothly but also extend its service life. By watching for signs of worn motor brushes, inspecting the brushes frequently, and adhering to good maintenance habits, you’ll keep your motor in top condition. 

Always remember, when in doubt, it’s wise to reach out to the motor’s manufacturer for detailed advice and suggestions on replacing carbon brushes.

If you have anything else you don’t understand, you can contact us by following Donghui Motor, and we will have professional staff answer your questions.


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