In this post we are going to construct a circuit to control the speed of 12V DC fan which is commercially available to run on 12V Solar panels and Batteries.
The utilization of DC fan become common where access to electricity is not established the area or where power cuts are pretty common or even on old model cars. In this situation battery powered fans come in handy. DC fans reasonably deliver air thrust as table top fans which operate at 230V/110VAC current.
If you want to save some power to by reducing the speed and prolong the battery life or if you want to adjust fan speed to your comfort, we need a fan speed controller which must not generate heat while throttling the speed.
The simplest way to throttle speed is to connect a variable resistor in series with fan, right? Wrong!
We can control speed by using a simple variable resistor, this method is very simple and very much inexpensive method, but why we do not prefer it?
Our goal for battery operated devices is to save energy as possible. The drawback of using variable resistor method is the excess energy is converted to heat; this will reduce battery life drastically.
To overcome this problem we are going for PWM which reduce power to the motor by switching the power on and off rapidly. The duty cycle or width of the on and off time determine the speed of fan, but the frequency remains constant.
Here is a very simple PWM generator using IC555, by varying the variable resistor, the pulse width can be changed. This is fed to MOSFET which is capable of handling higher current for the fan, the diode across fan suppress high voltage spike while turning the fan on/off.