DC Motor,Computer Cooling Fan Speed Controller Circuit DIY using Single Transistor And a Potentiometer

The circuit above can control speed of your DC motors or Computer Fans.If you use this to control speed of DC motors please use a diode to protect the Transistor,brush-less fans -OK.You can change the variable speed range by changing the value of R1 potentiometer.But don't use very high values,its pointless.

The transistor used here is a NPN 2n3055,it can handle up to 15A and 115W of power.And this transistor can handle up to 60V.So if you're using this for PC fans you can add more in parallel.Normally a computer fan uses about 0.4W of power.Some powerful ones may use about 7W of power.If you don't use so much power then you can use a low power transistor like C1061,D313 etc.

If you don't want to change the speed too often or hard to find a potentiometer or just willing to make this out of scrap you can use a Trim resistor for R1.

The transistor may heat up very much and its essential to use a Heat sink.If you can,do not solder the transistor to the PCB solder wires to its pins and attach a big heat sink for the transistor.Don't forget to apply some thermal paste.

Here is  the solder side and component side for this circuit's PCB.
Print at 300DPI,do not change any other setting while printing other than toner thickness.

For assistance in making PCBs please visit my article on How To Make PCBs at Home
Use a 4 1/2 drill bit for transistor collector holes [9/64in].
Checked and 100% working,feel free to ask questions.