How To Adjust The RPM Of A Two-Wire Cooling Fan?

Cooling fans are necessary components in electronic devices that generate a lot of heat. Without proper cooling, the internal components may overheat and malfunction. One of the most common types of cooling fans is the two-wire fan, which only has a positive and negative wire. However, one challenge with this type of fan is that it lacks the third wire, which is used for speed control. So, how can you adjust the RPM of a two-wire fan?
The answer: You cannot directly control the speed of a two-wire fan. It runs at a fixed speed, which is determined by the voltage and design of the fan. However, there are ways to indirectly control the speed of a two-wire fan:
1. Voltage Control: The speed of a two-wire fan is directly proportional to the input voltage. Lowering the voltage will decrease the speed, and increasing the voltage will increase the speed. One way to achieve voltage control is by using a voltage regulator. These devices can convert a higher input voltage to a lower output voltage. By adjusting the voltage regulator, you can vary the fan speed.
2. PWM Control: Pulse Width Modulation (PWM) is a method of controlling the speed of DC motors, including two-wire fans. PWM works by turning the voltage on and off at a very high frequency, which creates an averaged voltage. By changing the duty cycle (percentage of on-time), you can adjust the averaged voltage and hence the fan speed. To implement PWM control, you will need a PWM controller circuit or a microcontroller with PWM output.
3. Resistance Control: Adding a resistor in series with the fan can decrease the voltage and hence the speed. The resistor value determines the amount of voltage drop. However, this method wastes power and generates heat, so it is not very efficient.
4. Fan Replacement: If you require precise speed control or variable speed, you may need to replace the two-wire fan with a three-wire or four-wire fan. These fans have a dedicated wire for speed control, which makes it easier to adjust the speed.
In summary, it is possible to indirectly control the speed of a two-wire fan by manipulating the input voltage, using PWM, adding resistors, or replacing the fan. However, these methods have limitations and may not provide precise or efficient speed control. If you require more advanced cooling solutions, consider using a fan controller or other thermal management devices.
Reference:
[1] "How to Control the Speed of a Cooling Fan", Electronics Hub, https://www.electronicshub.org/control-speed-cooling-fan/