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Custom fan controller - Need help

post #1 of 4
Thread Starter 
Hey people.

I'm modding my case yet again, I will cut it up, change the cage locations, do a whole new front, change the power LEDs, put some new power buttons, drill some fan mounts, coat of paint, you know the drill.

Something came across my mind though. I figured out I can make a super cheap and effective fan controller out of a potentiometer, or variable resistor.

Now, i can't be arsed to order in a fan controller, since i don't have any in my vicinity. I'd like to approach the pot idea though, it'll only set me back a couple of cents. Maybe a few bucks for some 3-pin connnectors. I also like the challenge of homemade modding, so the "I made it myself" factor is also a pretty good incentive!

What i'd like to know is, can i put one potentiometer controlling various fans, let's say 6 for example? What specs would the pot need? What would happen to LED fans (any dimming?), would they be daisy chained or should I add a number of connectors?

I have soldering know how, just not alot of experience with component calculations. Anything i can learn off of this will be useful for future projects.

Any help and explanations would be appreciated!
Edited by Syde - 11/28/12 at 10:10am
post #2 of 4
All I can help you with is the LED dim thing and the answer is yes the LEDs will dim the less power you give the fans unless the fan has a separate LED power source which some fans do.
post #3 of 4
Thread Starter 
Originally Posted by Gawdz View Post

All I can help you with is the LED dim thing and the answer is yes the LEDs will dim the less power you give the fans unless the fan has a separate LED power source which some fans do.

Yeah, as I expected, thanks for confirmation. I think the dimming looks cool however, so no biggy there. I could always run the LEDs on a separate source if i really wanted to.

Still need help with that pot issue, but this subforum has relatively low movement unfortunately, so it might take a while.


I'm guessing the main thing here would be not to surpass the amprage limit of the potentiometer. So considering for example a 3w 20ohm pot running of a 12v line, after calculations it would have a limit of about 25miliamps I think.

If a daisy chain of fans surpassed that ammount of amperage, then i'd need a higher wattage pot. Is that relatively correct or not really?
Edited by Syde - 11/30/12 at 3:52am
post #4 of 4
Hi, personally I wouldn't go the big-watt-potentiometer route - after all, those things are pretty expensive, and essentially, you'll be wasting most of the energy going in when you dial your fans down (as in, probably most of the time).

If you want to keep it DIY, I think the simplest (and safest) thing you should probably look into is an L200 regulator IC. They cost around $2, can deliver anything from 3 to 36V at 2A to your fans, and they have all sorts of useful protections against overvoltage, overcurrent, overheating and so on.
If you have a look at the datasheet for those ICs, the recommended circuit (page 2/12, Fig. 1) for an application such as fan-driving incorporates two resistors, a potentiometer and two stabilizing caps (which are not really all that necessary for our purposes, since our power supplies are pretty well stabilized already I suppose), so it's not exactly a job that takes forever and a day to figure out and solder together. The actual circuit I'm using to power five fans in my case uses a 10k trimmer (= another potentiometer) instead of R1, and an additional 1k Resistor in series with the actual Potentiometer R2, since that makes it easier to have the potentiometer set to a useful range (so that your fans don't stall at the lowest setting - if you want that "off" functionality, better incorporate a switch into the circuit instead of sending a tiny bit of current through your non-moving fan motors continuously -that may badly affect their lifespan). The current limiting resistor R3 on my circuit is set to 0,5 Ohm (2x 1 Ohm in parallel), which gives out plenty of current to power those five fans - should limit the entire circuit to around 1A. If you don't care for overcurrent protection, just replace R3 with a straight wire or solder bridge, it will then limit at it's natural 2A heat-induced maximum. Speaking of heat, it might not be the worst idea to create a bit of a heatsink for the L200 - nothing too fancy is necessary, maybe a few washers and a screw, or just drill a hole through a bit of tin and attach it to the IC, with some thermal paste in between obviously. I personally just used a tiny GPU RAM cooler I had sitting around from a previous project. Thermal paste and superglue mixture does the trick in that case.

Edited by decnet - 12/2/12 at 4:05pm
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