How to Check if a DC Motor is Working Correctly

 

DC motors are widely used in various equipment due to their simple structure and flexible control. However, after long-term operation, even the best quality motors may have abnormal performance. So, what are the common manifestations when a DC motor has problems? Let's explain them one by one:

 

1. The motor does not turn or is difficult to start

This is one of the most common faults. Possible causes include:

· The brushes are severely worn and cannot contact the commutator;

· The armature coil is burned or broken;

· The power supply voltage is insufficient or the wiring is loose;

· The motor is stuck inside, such as bearing damage or foreign matter stuck in the rotor.

 

2. The speed is unstable or the operation is fast and slow

This situation is mostly related to the following factors:

· The brush has insufficient elasticity or poor contact;

· Commutator contamination or uneven wear;

· The armature is partially short-circuited or the inter-turn insulation is aged;

· External control system output voltage fluctuations.

 

3. There is abnormal noise or vibration

The DC motor itself runs relatively quietly. If there is abnormal noise or vibration, it is recommended to focus on checking:

· Whether the bearing is lack of oil, worn or stuck;

· Are there any loose parts inside the motor?

· The armature is unbalanced or the rotor is slightly deformed;

· Whether the installation foundation is firm.

 

4. The motor is overheated and even has a burning smell

Abnormal temperatures often indicate potential electrical problems:

· The current is too large, which may be caused by excessive load or winding short circuit;

· The motor is continuously running beyond the rated capacity without proper heat dissipation.

· Abnormal friction between the brush and the commutator, resulting in local overheating;

· The winding insulation is aged, increasing the resistance loss.

 

 

When a DC motor has abnormal behavior, many problems can actually be solved by yourself through some basic means. We recommend following the principle of "from outside to inside, from easy to difficult", and gradually narrowing down the scope of the problem. Here are a few key inspection steps:

 

1. Check the Carbon Brush

The brush is one of the most easily worn parts in a DC motor, which directly affects the starting and running stability of the motor. Focus on checking the following points:

Is the length significantly shortened? If the brush is excessively worn, it needs to be replaced in time;

Is the spring pressure normal? Insufficient spring force will lead to poor contact;

Is the brush stuck or misaligned? A stuck brush will cause the motor to not commutate normally;

Is the contact surface smooth? If there is abrasion, cracks or uneven wear on the surface, it means that there is abnormal contact.

Recommendation: Use a cotton swab dipped in anhydrous alcohol to clean the contact surface between the commutator and the brush to avoid carbon powder accumulation that affects performance.

 

2. Check the armature winding

The armature is the core component of the motor. Once it is damaged, the motor usually cannot operate normally. Inspection methods include:

Measure resistance: Use the Ω setting of a multimeter to detect the resistance between each winding in turn. They should be basically consistent (within a few ohms).

Observe the color of the winding: if it is obviously burnt black or has a strange smell, it means there is a short circuit or overload;

Check for inter-turn short circuit: You can use a professional inter-turn tester, or entrust a maintenance unit to check.

 

3. Check the wiring terminals and overall resistance

Is the wiring secure? Is there any oxidation, looseness or poor contact?

Is the power supply voltage up to standard? Use a multimeter to measure the input voltage to see if it is consistent with the rated value;

· Check the resistance of the whole machine: If the resistance is too high, it may be due to aging of the winding, poor contact of the brush or wiring problems.

 

4. Check the bearing condition and mechanical parts

Mechanical problems are also a common source of DC motor abnormal operation. It is recommended to check:

Manually rotate the shaft to see if it is smooth, and whether there is any stuck point or friction;

Is the axial/radial shaking abnormal? If the clearance is too large, it means that the bearing is seriously worn;

Identify faults by listening to the sound: If there is a "buzzing" or "clicking" noise during operation, it is probably because the bearings or internal parts are loose.

 

Tip: Make sure the power is off during inspection to avoid injury from electric shock or sudden start-up of the motor.

 

 

When troubleshooting whether a DC motor is working properly, using the right tools can greatly improve efficiency and safety. Here are some common basic tools and their uses, which are suitable for daily inspection and maintenance of most DC motors:

 

 

1. Multimeter

use:

· Measure whether the input voltage is normal;

· Check the resistance between the brush and the armature winding;

· Preliminarily determine whether the winding is open or short-circuited.

It is recommended to choose a digital multimeter with auto-ranging and buzzer functions for easy operation.

 

2. Screwdriver Set

use:

· Disassemble the motor housing and take out the brush assembly;

· Check the terminals or replace small parts.

It is recommended to use non-slip handles and magnetic models, which are more suitable for motor fasteners.

 

3. Cotton swab + anhydrous alcohol

use:

· Clean brush rails, commutator surfaces and terminal contacts;

· Remove internal carbon deposits, oil stains and impurities.

Note: Dry thoroughly after cleaning to avoid alcohol residue causing short circuit.

 

4. Endoscope or small light

use:

· Assist in checking whether there are foreign objects, damage marks or ablation inside the motor;

· Check the armature winding color and commutator condition.

 

5. Adjustable wrench or calipers (if bearings need to be replaced)

use:

· Remove couplings, end covers or fasteners;

· Check for bearing looseness or positioning accuracy.

 

 

After completing basic troubleshooting and testing, you may have discovered the problem, so the next step is to decide whether it is worth your time and effort to fix it.

Here are some common situation suggestions for your reference:

1. The brush and armature are severely worn or damaged

If the brushes have been worn to the limit, the armature has scorch marks or there is a short circuit between turns, the cost and labor cost of replacing the parts are often higher than that of a new motor body. In this case, it is recommended to replace the entire machine directly.

 

Applicable scenarios:

· Equipment that is older in use;

· The motor model is old or there are no ready-made accessories;

· Frequent changes have affected the normal production rhythm.

 

2. The motor has repeated faults such as continuous overheating and unstable operation

This type of problem usually originates from aging of the internal structure or winding damage. Even if it is repaired temporarily, it may recur soon. It is recommended to replace the motor as soon as possible to avoid affecting the safe operation of the whole machine.

 

3. Loose bearings, shaft shaking, and abnormal mechanical noise

Although the bearing problem may seem like a mechanical failure, long-term delay may cause the core components of the motor to wear or shift. If the motor is installed in a precise position (such as medical and automation equipment), it is recommended to directly replace the original motor of the same model to ensure mechanical accuracy.

4. The motor parameters can no longer meet the current load or control requirements

As applications are upgraded, the original motor may gradually fail to keep up with system requirements in terms of power, response speed, encoder output, etc. At this time, you can contact professional manufacturers to customize matching solutions instead of blindly repairing old equipment.

 

We recommend: Let professional manufacturers recommend alternative motors for you

If you find during testing:

· The extent of motor damage is difficult to determine

· No replacement products of the same model can be found

· Concerns about compatibility or installation issues

Please feel free to contact the VSD DC motor technical team. We can recommend alternative models free of charge based on your application requirements, or provide customized selection suggestions to help you quickly restore system operation and improve overall motor efficiency and life.

 

--A trustworthy DC motor manufacturer

 

When replacing or selecting a DC motor, choosing a manufacturer with reliable technology, timely service and stable products is often more important than simply choosing the "lowest price". As a company with more than ten years of experience in motor manufacturing, VSD not only provides standardized products, but also provides customers with the best solutions.

 

In terms of products, we provide a variety of DC motor products, including but not limited to: brushed DC motors, brushless DC motors, coreless motors, planetary gear reduction motors, and motors with encoders, which can be widely used in automation equipment, medical equipment, robots, transportation and other fields.

 

In addition to our standardized products, in order to better match customer products, we can also provide you with customized services based on drawings, actual objects or application requirements to ensure size compatibility, consistent motor parameters, and quick docking and replacement.

 

In terms of product technology and quality, we are also one of the best motor manufacturers in China. We have dozens of motor-related patents and have passed many international certifications such as ISO9001, CE, RoHS, etc. Each motor needs to undergo rigorous testing and aging verification before leaving the factory to ensure the quality of the motor.

 

Whether you need to replace an old motor or select a matching model for a new project, please feel free to contact us. Provide motor photos, nameplates, parameters or application scenarios, and we can recommend a matching solution for you!