Diy variable fan speed controller project

koochy_rat — Wed, 03 May 2006 14:09:14 +0800

My first simple project! It all started when I bought a new Vantec UV LED 92mm case fan to replace my existing one. Fan runs at 2600rpm, noise 33dbA. Before I bought it I thought it would be quiet enough.. but I was wrong! So had to find a way reduce noise.

I dug out some junk and managed to find parts to make a voltage regulator..
LM350 (LM317 is sufficient actually)
1k resistor
10k variable resistor
veroboard
1uF capacitor (from some unknown junk)
heatsink (from old broken PSU)
big 3 pin male socket (from old broken MB)
small 3 pin male socket (from old broken MB)
big 3 pin to small 3 pin cable (from old celeron)
ISA card back bracket (from old modem)

Total cost would be under rm5.. since I used mostly junk parts (there's value in junk!) LM350, resistors and veroboard were leftover from old projects. If you're lucky you can find all the parts needed from junk, so will cost next to nothing. To buy the parts I'm not sure where to get the 3 pin connectors and cable.. anyone knows?

This is the simple schematic.. pretty much standard. The capacitor on the output is optional.. just to smooth out the voltage. Some people put one on the inputs as well. But anyway it's just a fan so don't need so perfect output. The output voltage is calculated as 1.25*(1+(variable resistor)/1k), so if the variable resistor is max at 10k, output will be 11.25V.

The completed product! Two pins on the connector are 12V and GND. The remaining is the speed sense pin, which is direct connected to the output speed sense pin. Only two pins on the variable resistor are connected.. the middle and right one. So turning anticlockwise means max fan speed.

The back view.. cuts have to be made on the marked areas.

Installed in casing.. the input cable connects to my case's front panel fan rpm monitor, 3 pin connector. Output goes to the fan of course.

Back view of the installed controller.. the variable resistor was too tall initially, so it wouldn't fit. Had to cut and shave off the bottom part where the 3 leads are. Now it's just nice.. the nut and washer screws onto the case, making it extra secure.

The results! Set at medium speed, 1600rpm. Max can be achieved is 2200rpm. Voltage regulator takes up some power, so can't achieve the fan's rated 2600rpm.. will need a bypass switch for that. I wired the temp sensor to the heatsink.. slightly warm at 42C. I estimate it's dissipating about 1W of power, so nothing to worry about. The slower the fan speed, the hotter it will become. I haven't tried setting the fan slower bcos afraid will screw up the speed sensor.

Future:
Maybe add more fans.. still lots of space on the board for additional connectors. The LM350 can handle up to 3A of current.. so can control multiple fans together.

References:
http://casemods.pointofnoreturn.org/vregtu...orial-full.html
http://www.st.com/stonline/products/litera.../2154/lm317.pdf

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Diy variable fan speed controller project