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What can cooling fans do? Types, structure, control, and troubleshooting information

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1. What cooling fans do

When you hear the word "fan," you probably think of the electric fans and the ventilation fans used at home. But, there are other fans that are used in devices for cooling them. In recent years, fans have been increasingly used for purposes other than cooling, such as ventilation and air circulation.

2. Fan types

Fans are often classified by input power and shape.
There are two types of input power: AC (alternate current) and DC (direct current); they are called AC fans and DC fans. When classified by fan shape, there are three main types: axial fans, centrifugal fans, and blowers.
For example, if you see a product search filter "DC axial fan," this means that this refers to axial fans that support DC power. Fan manufacturers name their products differently, but there is no big difference in the classification.

Related Article: Training Session 2 - Fan Types

3. Fan structure

▲Fig.1 Cross-sectional view of fan
▲Fig.1 Cross-sectional view of fan

A cross-sectional view of a fan is shown. A cooling fan basically consists of the parts shown in Fig. 1, of which the most important is the ball bearings. All SANYO DENKI fans use this two-ball bearing design. This reduces the bearing load, increasing the fan reliability and extending the service life.

▲Fig.1 Cross-sectional view of fan
▲Fig.1 Cross-sectional view of fan

Related Article: Training Session 3 - Service Life

4. Control of fan rotational speed

You can control the rotational speed of a fan with PWM control. PWM control is a function that controls the rotational speed of fans by changing the pulse width of the control signal, and allows a wider range of control than when controlling by voltage. To use the PWM control, you need a circuit that generates PWM signals.
If you find it difficult to make one on your own, SANYO DENKI offers a PWM Controller that allows you to control PWM fans without having to design a circuit. We also offer the San Ace Controller, an IoT-ready product for the remote monitoring and control of fan speed.

5. How to reduce large/unusual fan noise

If a fan built in equipment makes unusual noise, it may be hitting the equipment as it rotates. This can be solved by attaching anti-vibration rubber for absorbing vibration. Another possibility is that the equipment is in resonance with the fan. In this case, it is necessary to increase the rigidity of the equipment so that the speed of the fan and the equipment do not resonate.

▲Fig. 2 System impedance and P-Q performance curves
▲Fig. 2 System impedance and P-Q performance curves

If noise comes from the fan itself, the following three potential causes are possible:
Wind noise: Turbulent noise that rotating blades produce
EMI (electromagnetic interference) noise: Motor switching noise, etc.
Mechanical noise: Vibration noise due to unbalanced rotor

These are determined in the fan manufacturing process, but the "wind noise" can be reduced by adjusting the fan speed using the PWM control. Since the sound pressure level of a fan varies depending on the speed, it is best to set the speed for the lowest noise level. However, this also changes the airflow and others, it is difficult to find the best setting where both the cooling performance and low noise are achieved.

So, if you want to achieve quietness while maintaining the optimal cooling performance, it is recommended to select a fan after taking into account the fan's optimal operating point based on the system impedance of equipment and P-Q performance of the fan.

▲Fig. 2 System impedance and P-Q performance curves
▲Fig. 2 System impedance and P-Q performance curves

Related Article: Training Session 7 - System Impedance of Devices

Date of publication: March 8, 2021

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