A DC fan is a well-known and commonly used thermal management device that can be used alone, in series or in parallel to provide forced air convection cooling. It is precisely because of the versatility and relatively simple operation of the DC fan that it has been a solid choice for temperature control technology in the final application for many years.
According to the fundamental laws of physics, the airflow generated by the fan will absorb the heat of the device to be dissipated and take the heat away from the device to be dissipated, thereby effectively cooling the device components. However, the effectiveness of heat dissipation is affected by several factors; engineers will benefit from a better understanding of the existing functions and various options of DC fans, thus improving reliability and efficiency.
Before selecting the DC fan, the engineer needs to stop some basic thermal analysis, in order to calculate the minimum air volume request. A typical thermal profile may include modeling of heat sources, environmental conditions, and temperature rise. In addition, other factors such as fan size, direction of rotation, and airflow paths within the application need to be thought through to ensure an appropriate treatment plan.
After completing the thermal profile and selecting a fan of the appropriate size and rating, the next step is to energize the fan and make it work, right? Although continuous operation of the fan can achieve its purpose under certain conditions, continuous forced air cooling usually does not achieve energy savings or provide a long-term treatment plan. Today's DC fans offer designers a range of control, monitoring and maintenance options for enhanced thermal management.
Start/stop cycle
As mentioned above, the continuous operation of the fan will definitely insist on cooling the temperature-sensitive parts, but it will ignore its power consumption and the fact that the life of the moving parts of the fan is limited. Fan operation also produces audible noise, which may be prohibitive in a variety of applications and environments.
Stopping start/stop operation of the fan based on the temperature setpoint is an alternative, which can eliminate some of the disadvantages of continuous fan operation. The use of fan start/stop control technology can save energy by limiting the running time, reducing the stress on the moving parts of the fan, and stopping the fan when the temperature drops below the set value, thereby reducing the audible noise.
However, the start/stop fan control oversimplifies the forced air cooling approach in many ways and is inherently flawed.
First, the start/stop control technique performs a hot and cold cycle for temperature sensitive components. Thermal cycling is even more damaging to critical components than operating at constant high temperatures. This is due to thermal cycling will produce temperature coefficient differences, resulting in data and solder joints to receive additional stress, resulting in premature failure.
The second is the unpreventable thermal overshoot factor. This is the time delay between the forced airflow generated by the fan starting the micro-fan and the beginning of the actual cooling. During this time delay, the component may overheat unless the Fan Start setpoint is lowered. Moreover, by lowering the set point, the time for the fan to power on and produce audible noise also increases. Finally, to prevent rapid start-stop (often referred to as "chatter") near the set point, the demand is retarded.
Selection of fan control function
Today's DC fans offer designers a range of control and maintenance options for more sophisticated thermal management systems. These advanced designs take the fundamental start/stop fan control to a new level of performance, efficiency and robustness. In addition, a maintenance option is provided to detect problems before damage to the micro-fan cooling components of the formation fan. Here are some of the most common fan control and maintenance options:
pulse width modulation
Pulse width modulation (PWM) is a common method used to control and change the fan speed according to thermal conditions that change from time to time. With the use of advanced control algorithms, based on the PWM variable speed control can improve the operating efficiency, and can adapt to the fan speed and thermal load matching operation dynamics.
Fan start/stop control can also be advanced through the use of proportional integral derivative (PI and PID) closed-loop control techniques. These strategies ensure airflow conditions at the desired temperature set point, which helps prevent thermal overshoot or undershoot when the load changes.
Embedded Tachometer Signal
The embedded tachometer is used for closed-loop reaction and more advanced fan control, and the fan speed can be detected and reported by measuring the frequency of the pulse output signal. The tachometer can also be used as a lock sensor to alert the user when the fan stops running due to power failure, blockage, etc. The ability to detect these problems as quickly as possible is a major advantage of system operation, and the ability to shut down in time to maintain temperature-sensitive components.
Automatic Restart Maintenance
The automatic restart maintenance function detects when the fan motor is prevented from rotating and automatically cuts off the drive current. This makes it possible to maintain the fan drive circuit and notify the fan controller of an urgent problem caused by the cut-off of the drive current.
Rotation detection/lock sensor
The rotation detection/lock sensor is used to detect whether the fan motor is running or stopped, which can avoid problems during startup or operation.
Summary of this paper
When the application generates excessive heat, DC fans are a common cooling choice, which can keep the equipment components within the extreme operating temperature range and improve heat dissipation performance. After some fundamental thermal analysis, the continuous running fan is undoubtedly a good cooling choice, but more advanced control and maintenance functions can make the fan have a longer service life and higher efficiency.