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Free projects are only for private use and not for commercial use.
U-Ham Group have all the rights on all these free projects and could make changes at any time without any prior notice, so be updated frequently.
User can use the projects at his own risk.

Temperature dependent fan speed controller


Features  fan controller 

  • Adjustable start point

  • Voltage operating range: 9v-15v

  • Maximum temperature sensor cable length  1 meter

  • LED indicator light for fan operation

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It concerns a simple circuit to control the speed of a cooling fan based on the temperature measured by a temperature sensor (thermistor) placed at a suitable point on the P/D to "read" as closely as possible the output temperature of the machine. It is of course recommended to use a quality thermal paste for more reliable results.

The whole circuit is designed on the property of the thermistor to change its internal resistance depending on the temperature change in its body. This one is of negative temperature coefficient -Negative Temperature Coefficient or otherwise NTC, which reduces its resistance as the temperature rises. This causes the mosfet Q1   to trig proportionally to its gate and by extension  to affect the voltage of the fan and make it increase revolutions proportionally.

There is a voltage threshold above which the fan starts to spin and in which the setting of VR1 plays a decisive role which creates a voltage divider and beyond that the revolutions depend proportionally on the temperature affecting the thermistor. The reverse also applies in case of a decrease in temperature.

How to adjust the temperature sensor.

  • Locate the VR1 regulator. Connect the voltage 13.8VDC  and the fan as in the photo.

  • Press the sensor with two fingers and with a screwdriver adjust VR1 until the fan is ready to start and the LED just starts to light up.

Normally, this setting causes the fan to start slowly as the temperature reaches about 36°C and then increase the fan speed as the temperature rises.

The opposite happens when the temperature drops and below 36°C the fan slows down until the falling voltage level cannot keep it spinning.

  • Turn VR1 until the fan is at such a speed that it keeps the temperature at the level you want and if you want to change it from the set 36°C.

  • Place the fan far enough away from the P/W heatsink that it will be effective, but not so close that it touches, as the reflected airflow comes back through the fan body and cancels the flow itself.

Linkage  (Applies to off-the-shelf device)

Watch out for any mistakes especially in the position and polarity of the 13.8VDC wiring.

The subpoenas can be seen in the photo.


The board was designed to match the specific plastic box

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