Using Diodes for Fan Control.

This in alternative to using rheostats and chips for controlling fan speed.

The idea for this came from http://www.cpemma.co.uk/sdiodes.html NOW http://www.pcsilencioso.com/cpemma/sdiodes.html and I wanted to explain it a little more and build a few of them. Basically a diode type 1N4001 drops around 0.75 volts with a typical fan. When you link them together then the voltage can be varied.

This is taken from the site
Using a chain of diodes mounted on a rotary switch, a series of voltage steps can be produced giving adequate control for fans.

This control method has several advantages;

• Cost is less than that of a half-decent rheostat, and much less than the price of a good one.
• number of fans wired in parallel (or to a fanbus) can be controlled from the unit without danger of overload. Cheap rotary switches will handle 1amp at low voltage, rheostats to handle such currents are big and expensive.
• The full 12V can be used if required. Basic semi-conductor voltage regulators lose about 2V and would need a by-passing switch to run the fans at full speed.
• The heat produced is spread over a number of diodes. Each one will only generate about a watt at the maximum 1amp load, and less than 0.1W per diode with a typical single fan.
• Unlike resistors, voltage drop is about the same at all fan currents, so fan start-up at low voltages is more assured and a wide range of fans can be used on the same unit.
• Last but not least, adding display lights to form a voltage bargraph or show switch position is easy.

This is my adaption to the original idea. I will use the pictures from the site to help explain.

I did one of the switches as a speed up video.

Their are several ways that LEDs can be used for this to show what setting the switch is on.

• Bar graph
• single Indicator
• No LEDs

The pictures help explain.

The wireing positions for the LEDs on a 2P6P rotary switch are 7-12.

You can do like what I did for the LEDs or do them like the diodes in Steep 4 if you want to do a bar graph.

I added a wire to each position (7-12) Then did the diodes type1N5817 Schottky diodes on a PC board.

I will show how to do the LEDs later on another Instructable.

The are also options for doing the diodes for the fan control.

This is from the site

If you don't want lights, just use the left-hand section of the schematic, for pole 'A'. Using a 12-way 1-pole switch. This would allow the range to be extended, using single diodes between each position. You could then use 1A Schottky diodes, they drop under 0.5V per diode so would give smaller steps, and/or have an unconnected "off" position at one end.

For my switches I used 6 Diodes(Type1N4001). I did my wiring like this.

• no diode for full 12v
• 2 diodes
• 2 diodes
• 1 diode
• 1 diode
• No diode for off (later updated to 2 diodes for a very low speed)

I used the 2 pin power wire that came with the fan,

I removed the yellow and the black wire from the plug and sniped the old 2 pin power wire off at that end. Then stripped a red and a black wire for power and ground. Red wire was pushed into the hole in the molex pin and soldered the same thing for the black wire fro ground. Afterward they where heat shrinked and pushed back into the molex plug.

connect the ground on the molex to the ground to the fans 2 pin ground wire. Then the red wire from the plug goes to the wire on position 6 of the rotary switch. Position A gets attached to the power wire on the 2pin fan power wire. Then heat shrink.

Make sure all solder connection have heat shrink. Plug the fan in and then plug the molex in.
You should now be able to control the fan with the rotary switch.

I will make a new instructible for doing the LEDs or add to this one later on.This is what id did with mine. I forgot to take pictures when i made it, but I am making one more.


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Thank You CPEMMA for letting me use pictures and text from your website.