In our daily lives, we can't do without cooling fans in summer—so... Cooling fan When it’s running, has anyone ever wondered how its motor works? A fan motor essentially generates force and the effect of that force.
We’ve already learned about the conversion between force and electrical energy in physics class. Now, let’s share some professional insights with everyone!

We’ll divide it into three volumes: upper, middle, and lower.

Divided into five chapters.

Chapter 1: Overview of Motors

Chapter Two: Operating Principle of the Motor

Chapter 3: Motor-Controlled Drive

Chapter Four: Motor Performance

Chapter Five: Other Motors

Chapter 1: Overview of Motors

Definition of a motor: It is an electromagnetic device that converts or transfers electrical energy based on the law of electromagnetic induction.

Note: 1. The field of motor design encompasses a wide range of knowledge areas, including electromagnetics, mechanics, thermodynamics, and materials science. Importantly, the challenge lies in identifying an optimal design at the lowest possible cost. The motor design process is extremely complex and requires continuous verification to ensure that the aging parameters of the design meet the required specifications.

2. The determination of the motor’s application requirements—specifically, its size and load demands—is primarily based on the motor’s dimensions. Generally speaking, the motor’s volume is directly proportional to its output power. The load requirements include the rated speed, rated output power, and rated voltage; the determination of these parameters is closely related to the specific application environment of the motor.

Cooling fan DC brushless motor

The brushless DC motor uses a non-contact position sensor and semiconductor components to replace the commutator and brushes, enabling motor operation through electronic switching. This eliminates the wear-and-tear issues associated with brushed motors, achieving high performance.

Chapter 2: Operating Principle of Cooling Fan Motors

Starting from the VCC power supply, using the left-hand rule, we can see that the magnetic field repulsion causes the motor to rotate.

Chapter 3: Motor Control and Drive

When a magnetic field B, oriented perpendicular to the surface of a conducting semiconductor wafer, is applied across the wafer, a voltage appears across its lateral edges. This phenomenon is known as the Hall effect (discovered in 1879 by the scientist Edwin Hall).

Hall devices—such as the Hall sensors currently used in cooling fans—include models 277, 276, 177, and 101. The drive chips involved are LB11867 and 11961. However, with advances in science and technology, today’s drivers are increasingly being replaced by MCUs that run programs and are then programmed onto the chips, rather than relying on the original drive chip 11867.

Chapter 4: Motor Performance

1. Power supply voltage:

The voltages we commonly encounter include: 5V, 36V, 48V, 18V, 12V, 3V, and 24V (voltages below 36V are considered standard voltages; voltages exceeding 36V must undergo 3C mandatory certification). The measurement method uses a multimeter.

2. Rated torque:

Simply put, it refers to the magnitude of the rotational force (units: kg·cm, N·m). This force directly determines the rotational speed of the cooling fan. Previously, the testing method was too cumbersome, but now it can be measured using instruments.

3. Rated speed:

Rotational speed per minute. (Unit: n/min, RPM).

Typically, we allow a 10% margin of error for customers, but in practice, we can keep the error rate within 5%, except for special requirements. Now, with the help of an MCU, we can further reduce the error rate to as low as 2%.

Testing method: Infrared tachometer, internal flash frequency generator, tested using an FG waveform analyzer.

4. Rated current:

The current consumed during operation is directly affected by the coil impedance: I = U/R, where I is measured in amperes (A) or milliamperes (mA).

Measurement method: ammeter—now conveniently displayed directly on the DC power supply.

5. Start torque,

This refers to the torque at the moment of startup, which is determined by the starting voltage. Typically, it is less than 1/1.6 of the rated torque.

6. FG/RD waveform output

7. Insulation level and insulation resistance

Insulation Resistance (JEC-146)

After the motor is assembled, an insulation withstand test is conducted on the motor using a power-frequency sinusoidal AC voltage.

Apply 500 + 2E (where E is the maximum operating voltage of the motor, up to 50V) between the coil and the iron core for 10 minutes.

Note: First apply 250V, then 500V, then 250V, and finally disconnect the power.

Insulation resistance: (JEC-37)

To ensure the insulation strength between the motor’s charging section and ground, measure using a 100V insulation resistance tester.

Test: OK for 0.5M and above; AC—1M and above. 500 + Rated Output + 1000 = Insulation Resistance 0.

8. Cooling fan noise

Noise is the absence of sound—when there’s no sound, there simply is no noise. It’s typically measured in decibels (dB).

The testing method, according to the standard, offers two distances: 1 meter and 0.5 meter. Typically, the difference is several dozen dB.

Our specifications: (ISO 7779, ISO 3745)

Semi-anechoic chamber, axial direction: FAN axial distance 1 m

Duration: 10 sec

Measure three times and take the largest value.

9. Temperature rise

The temperature rise refers to the difference between the motor's temperature and the ambient temperature.

Including operating temperature rise and locking temperature rise.

Measurement methods: thermometers, resistance method, temperature-indicating materials, and optical methods.

The components that must be measured at high temperatures under stable conditions are those that can be accessed. Typically, we run the equipment for several hours before taking measurements.

The locked data will be available after 24 hours. We applied for UL certification and received a Class A rating.

Standard: (JIS C 4003)

Y 90 °C

A 105°C

E 120°C

B 130°C

F 155°C

H 180°C

C exceeds 180°

10. Operating temperature and humidity

Customers generally require cooling fans to operate within a temperature range of -10 °C to 60 °C; we have expanded this range to -40 °C to 85 °C.

The humidity requirement is generally 65% relative humidity. We have measurements showing 95% relative humidity at 60°C.

The purpose of setting this condition is to enable the use of computers and other devices when skiing on the Qinghai-Tibet Plateau and swimming in the Mediterranean Sea.

Relative humidity:

It refers to the percentage of water vapor that the air can hold at a given temperature. In a bathroom immediately after taking a hot shower, the air is already saturated with moisture, meaning the relative humidity is 100%. That’s why you see water droplets condensing on the mirror. In summer, the relative humidity is typically very high—often exceeding 80%.

11. Vibration

Vibration resistance is tested using a specialized test platform.

Our test is set to [CNS5076(C6051)].

Displacement: 0.75 mm

Frequency range

1. 10 Hz ~ 55 Hz / 30 seconds

2. 55 Hz ~10 Hz / 30 seconds

3. Linear scanning / 120 cycles / X, Y, and Z axes

Impact resistance (IEC68-2-27)

Condition: Half-wave

Acceleration: 50G

Axial: x, -x, y, -y, z, -z

Duration: 11 ms

Each axis is impacted three times, for a total of 18 impacts.

12. Name of Longevity

For cooling fans, the key factor depends on the service life of the bearings.

B is 70,000 to 90,000 H.

C is 30,000 to 40,000 H.

S ranges from 20,000 to 25,000 H.

T is 45,000 H.

There are two ways.

1. Tighten the test conditions, shorten the test duration, and then calculate the lifespan using a formula—this is known as the accelerated life testing method.

For 9020R, we’ll test it according to 1732H.

2. Let the fan run under standard conditions (25°C, 65% relative humidity) until the time recorded under the adverse conditions is reached.

When using accelerated testing, each company often employs different calculation methods, leading to significant variations in the resulting service life estimates. As a result, many manufacturers now refuse to accept such data. Moreover, the second approach requires a very long time frame and specialized facilities, making its implementation quite challenging.

Moreover, the criteria for determining defects vary among different customers or manufacturers, which also affects Shouming’s data. For example, some specify that a speed below 30% is considered defective, while others set the threshold at 10% or lower.

13. Weight, protection method, rotation direction, number of FG pulses

Weight: refers to controlling the overall mass of the cooling fan.

Protection mode: Equipped with automatic reset function.

Rotation direction: Clockwise or counterclockwise?

FG pulse count: typically two pulses per revolution.

Chapter 5: Other Motors

1. Understanding the Starting Voltage

The start-up voltage refers to the minimum operating voltage required for the fan to run at low speed. It’s an important characteristic used to evaluate a fan’s performance. Generally, fans with lower static friction coefficients and Hall ICs that operate at lower voltages are able to start up the fan at a lower electrical input.

The factors that affect the fan’s starting voltage include:

1. Is the winding design appropriate?

2. The magnitude of hysteresis loss in silicon steel sheets.

3. Low operating voltage of Hall IC

4. The high or low gain of the transistor.

5. Magnetization strength of rubber magnets.

6. The weight of the fan blades.

7. The magnitude of the bearing’s coefficient of friction.

8. The magnitude of the transistor saturation voltage.

9. Is there a reverse protection diode?

II. Recognizing the dead zones of cooling fans.

The so-called “dead zone” of a cooling fan refers to the situation where, when the fan is positioned at certain angles, it fails to start up at the specified voltage. The testing method involves sequentially adjusting each terminal of the fan relative to the Hall IC, then gradually increasing the voltage until the fan starts up. If any terminal starts up before reaching the specified voltage threshold, the fan is considered qualified. However, if there are significant differences among the terminals—meaning some terminals start up at voltages exceeding the specified threshold—the fan is classified as having a dead zone.

The factors that affect the fan’s starting voltage include:

1. The magnetic poles of the rubber magnet are unevenly magnetized.

2. The Hall IC’s sensitivity is too poor.

3. The magnetizing magnetic field of the rubber magnet is too weak.

4. Incorrect placement of the HALL IC position

5. Excessive mechanical friction

6. Silicon steel sheet angle and material issues

The above is an overview of the operation and working principle of cooling fan motors. For more detailed information and additional resources, please visit our company’s official website: Shenzhen Jiangshanlai Electronic Technology Co., Ltd.—a reliable supplier of cooling fans!