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How Do I Know If My Brushless Motor is Bad

In the world of manufacturing, the reliability of machinery plays a role. Any malfunction can disrupt production, leading to downtime, increased expenses, and unhappy customers. One crucial component among these machines is the DC motor, which powers numerous operations.

However, these motors can experience issues over time, like any mechanical system. As a professional in the manufacturing field, it’s essential to be observant and attentive when it comes to monitoring the health of your brushless motors. This guide highlights the signs indicating problems within these indispensable workhorses.

Now, let’s embark on this journey of diagnosing and maintaining your equipment – ensuring that your manufacturing processes run efficiently.

What Can Go Wrong With a Brushless Motor?

Brushless motors have become indispensable components in various industries, driving everything from machinery to automotive systems. Nonetheless, they remain susceptible to problems impacting their performance and dependability, similar to any technological system. Let’s explore two critical pain points businesses may encounter when using brushless motors.

Reaching Higher Temperatures

One of the concerns when it comes to brushless motors is their tendency to generate heat while in operation. Despite their reputation for being efficient and consuming energy, the temperature rise can pose a challenge. This is particularly crucial in settings where motors are pushed to their limits.

The increased temperatures can result in problems, including;

● Reduced Efficiency: Excessive heat can cause the motor to function efficiently, leading to energy consumption and decreased overall performance. Consequently, businesses may incur costs.

● Shortened Lifespan: Prolonged exposure to temperatures can significantly decrease the lifespan of brushless motors. This premature motor failure may necessitate replacements. It causes unnecessary downtime.

Irregularity While Spinning

Another common issue businesses encounter when using brushless motors is spinning or erratic performance. This irregularity can manifest in ways such as stops, variations in speed, or vibrations.

These irregularities can be caused by factors, like;

● Sensor Issues: Malfunctioning sensors may provide feedback, causing the motor controller to adjust.

● Electromagnetic Interference (EMI) poses a challenge to motors functioning, causing them to spin irregularly. 

To address this issue, companies should invest in top-notch sensors and protective measures that effectively minimize the impact of EMI. Regular maintenance and calibration of sensors are also crucial to ensuring smooth and reliable motor performance.

What Makes Brushless Motors Different?

Brushless motors, an achievement of engineering, operate based on an intriguing principle known as induction. They differentiate themselves from their brushed counterparts by utilizing a combination of electrical magnets, which are set into motion through the power of induction. Let’s explore the factors that distinguish brushless motors and their application advantages.

At the core of a brushless motor lies three wires for supplying a trio of phase-shifting AC currents to the motor. This elegant and efficient design greatly enhances performance while significantly reducing wear and tear compared to brushed motors.

One notable feature of brushless motors is their accompanying Electronic Speed Controller (ESC). Unlike brushed motors that can be directly connected to a power source with speed varying based on voltage, brushless motors offer control through the ESC. This electronic marvel lets users quickly manipulate motor speed by modulating levels and signals.

However, there is a trade-off for this user functionality. Monitoring and diagnosing motor issues require a “dry testing” technique for brushless motors. While the ESC simplifies operation, troubleshooting requires a skill set. Dry testing involves assessing your brushless motor to ensure it functions optimally.

Ensuring the dependability and durability of these motors is an aspect, particularly for businesses that heavily rely on them for their operations.

Brushless Motor

Testing a Brushless Motor

Ensuring these motors function effectively can mean the difference between seamless operations and costly downtimes. How can you tell if your brushless motor might be on the brink of failure? Let’s delve into it.

Step One: Identifying Motor Issues

Disconnect your brushless motor from the Electronic Speed Controller (ESC) to properly test it. Use a battery-operated drill with speed. Hold the stationary part of the motor securely while keeping the three lead wires separate.

Operate the motor at its designated speed for a few minutes, carefully observing its performance. If you hear any noises or notice the heat inside the motor, it could indicate a problem, such as a shorted winding or loose magnet colliding with the stator.

Step Two: Checking Motor Wires

Assign labels (1, 2, and 3) to each motor wire, ensuring they are kept separate. Then, connect your voltmeter to an AC range. Attach two wires to terminals 1 and 2. Again, set the drill to its speed and take note of the AC voltage reading.

Please replicate this procedure, treating terminals 2 and 3 as terminals 1 and 3, respectively. The objective is to make a comparison based on these readings. If all three readings are not roughly equal, it suggests an issue with your motor wires.

Step Three: Searching for Short Circuits

This step involves examining whether there are any circuits between the stator and windings.

Examine the correlation between the windings and laminations within the motor stator. To perform this assessment, identify a stator section with exposed metal for a one-meter connection and the windings for the other.

If you encounter difficulty locating exposed metal, you can generate a conductive surface by piercing the protective coating on the steel laminations. It is essential to highlight that the integrity of your motor may be compromised if the meter fails to register a complete circuit.

Step Four: Final Inspection

You can consider your motor function if all the previous tests have passed. However, checking the motor’s no-load current before reinstalling it is advisable. Compare this measurement with the manufacturer’s provided specifications. This step is crucial for identifying any turns or windings in the motor that may have become shorted out.

If you detect a turn, it is imperative not to use the motor as it can generate heat, potentially resulting in motor failure and even damaging your Electronic Speed Controller (ESC).

How to Identify a Failing Brushless Motor: Key Indicators

In the dynamic world of manufacturing, the reliability and efficiency of machinery are paramount. Brushless motors, lauded for their maintenance-free operation and longer lifespan, are not immune to wear and tear. The ability to promptly detect signs of deterioration can save both time and capital for businesses. Here are some vital indicators that your brushless motor may be on the brink of failure:

Brushless Motor

Unusual Sounds 

Motors should run smoothly. If your brushless motor emits abnormal sounds such as humming, whining, or grinding, it’s a clear sign that something is amiss. Such noises can hint at mechanical faults or internal wear.

Physical Signs

A visual inspection can often be revealing. Check for any overt signs of damage. This could be external wear, visible internal damage when inspected, or even an unusual accumulation of dirt and debris, which can hamper its function.

Performance Issues

A motor’s operational performance speaks volumes. If your brushless motor experiences lags, stalls, or shows RPM inconsistencies, it could be an early warning sign of impending failure. Such irregularities indicate that the motor isn’t functioning to its optimal capacity.

Click to read our article: How to Test and Troubleshoot Brushless Motors

What to Do After Your Brushless Motor Test

After evaluating the brushless motor, your next steps become crucial to ensure that your machinery maintains its efficiency and reliability. Below is a guide to help you effectively navigate the test phase;

Successful Test Outcome

Congratulations! A positive test result indicates that your brushless motor meets the standards. You can proceed with reinstalling it into your equipment for use. However, remember maintenance. 

Ensure to incorporate the motor into your maintenance schedule to monitor its performance over time. Regular checks and preventive maintenance are essential for extending equipment lifespan and avoiding breakdowns.

Failed Test Result

If any conducted tests reveal issues with your brushless motor, it’s crucial to take action. Depending on the problem’s severity, consider repairing or replacing the motor. Contact your maintenance team or a qualified technician who can accurately diagnose the problem and determine the cost solution. Delaying action could lead to damage and costly downtime.

Whether you pass or fail these tests, remember that regular testing and maintenance play roles in managing manufacturing operations. By taking an approach, you can reduce interruptions, improve efficiency, and guarantee the durability of your brushless motors.


Establishing the integrity of a brushless motor is imperative for businesses to ensure seamless operations and to safeguard their investments. 

While the nuances of brushless motor functionalities are vast, there are definitive signs to ascertain their operational state. Often, if a motor emits unusual sounds, struggles to maintain consistent speed, heats up excessively, or presents electronic disturbances, these are clear indicators of potential issues. 

Discrepancies in RPM readings and unexpected system halts might also raise flags. Regular maintenance and frequent checks are essential for longevity and the safety and efficiency of the entire system. Consistent observation, timely inspections, and immediate action upon spotting irregularities are pivotal to ensuring that your brushless motor is in optimal condition.

If you don’t understand anything, you can contact Donghui Motor and we will answer your questions.

Related Reading: How Does a Brushed Motor Work?


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