DIY fan controller?

[faceless105]

anyone ever came across these before?i'm workin on a fully custom case and i'd love to have a DIY fan controller, not jsut because i want it to be a custom build, but i want to be able to order knobs that go with the case.

... it's kinda a retro case so simple small black knobs wouldn't go to nicly with it, lol

[dgrmkrp]

if u wanna build something for fan controlling needs ..then what u should buy are the following:

http://grtmars.com/images/potent.gif
a pot (should have between 5Kohm and more.. it doesn't really affect the final resitance, as long as you don't go with <0.5Kohm)

http://www.electronix.com/catalog/images/bathtub.jpg
a resistor like this one (do not use small wattage like 0.25W ..use something as 20 or 30ohm@10W)

wired like this:
http://i10.photobucket.com/albums/a141/dgrmkrp/misc/4148a4ce.jpg
the parallel connected resistor will change the assembly resistance to it's own :) so, depending on the fan, u can lower its speed/noise even to the point it barely functions.. cool, right?

[faceless105]

definatly cool, though could you kinda explain the technical aspect to me, likw how you ended up with those pots and resisters? i've read other places that use only a 50-100 ohm pot, and i keep finding real inconsistencies around this. i know that they're all custom design and they probably yeild the same result, but would you mind explaining it just a little to me?

[dgrmkrp]

sure.. no problem:

the principle is the same, but the availabilty of the parts made me choose this design. basicly, u want to add resistance (in series) to the +12V line before the fan + input to lower the voltage the fan sees. this translates almost linearly into lower speed. less voltage=less force for the motor to spin. the negative(black) wire is connected either straight to the fan, or to the third leg of the pot, which does nothing.. i prefer the direct method if the circuitry is not that complex..

basic physics say that when u put 2(or more) resistor in parallel, the final resistance is (1/R)=(1/r1+1/r2). so if u have on resistance far greater than the other (r1=30ohm, r2=10000ohm), when you invert the values you get one that is close to 0 (1/r2=1/10000=0.00001 ~0), u end up with the assembly having the resistance of the smaller one... voila! u can control the voltage!

in case of some commercial controllers, instead of using resistor, transistors are used to keep the final voltage steady, irespective of the load seen. in our case, who don't know how to do that (yet.. hihi), we must calculate the R value based on the load of the fan(s) the controller sees. u can calculate this by... well, too much said.. what u need to know is that the more resistance, the less voltage, so using 20-30 ohm lowers the speed a litle.. using 100ohms may stop the fan completely... try things for your case, as resistors are cheap.

have fun

[faceless105]

hey thanks. i'm definatly going to be tryin this one out. i figure worst case scenario i can go get a commercial fan controller, but i'd really rather try this approach, thanks again, i wont know the results for about a week when i have a free chance to try this all out though :(

[justblair]

Can I direct you to this webby. The owner is a contributer at SPCR and other modding forums.

On it is a number of circuit schematics for diy fan controllers with a very detailed explanation of their pros and cons. The circuits are easy to make in most cases.

I would personally use an adjustable mosfet regulator such as an LM350T with an adjustable resistor to set the voltage. PWM is also good in most cases, though some fans have a tendancy to click or give off other noise when controlled this way.

http://www.cpemma.co.uk/