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Fan controller DIY

post #1 of 17
Thread Starter 
So I'm planning on making a little dial which will go on my desk to control the rpm of my case fans (long story short, my desk is my case so putting the dial there is just like putting it on the outside of a case). I have some basic soldering skills and electrical knowledge but I don't really know much about computer fans. Does anyone know what type of fans I might need? I'm also thinking it would be cool to have a little lcd saying the fan speed but it's not necessary. So in essence I want to know the types of connections my fans would need to have in order to get the most flexibility in creating a fan controller for them.

Oh, and the fans will all just run at the same speed, I don't want individual control. If you've seen this done anywhere else let me know too, thanks! cheers.gif
post #2 of 17
All you need is a rheostat.
Sidewinder computer

If you buy one from an electronics store it will cost about $10

You can use any fan with it. You only need the power and ground wires from the fan to control it's speed, no matter how many wires the fan actually has.

Just make sure that the combined wattage of all the fan you hook up to it is less that it's 25 watt capacity. If one rheostat isn't enough, use two, or buy one with a higher wattage rating. That's a very heavy duty part. I used that exact one (for three years) to control three Delta FFB1212EHE fans that draw 24 watts each. The rheostat didn't burn out, but ran very hot when the fans were slowed down a lot (slower = more watts to dissipate as heat instead of sending then to the fan(s)

You could also hook the tachometer wire (usually the yellow wire) from any fan to a monitored motherboard fan header (one fan per header) and you'll be able to monitor the speed of that fan, either in the BIOS or with software like SpeedFan, HWMonitor, etc..

It's a lot easier than you thought?
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post #3 of 17
What billbartuska said. thumb.gif

Lot of them on ebay too. wink.gif
post #4 of 17
Thread Starter 
Thanks @billbartuska, I already figured that I could just use a rheostat, was just wondering if there was a better way (not much point in wasting power). I have seen someone design theirs so that it was feeding power back to the power supply but I'd rather not mess with a power supply tbh. So with monitoring the fan speed, is there any way to get a hardware implementation so that I don't have to rely on the OS having booted up and always running a background program? Also, how do you get power to the fans as you would connect the fans in parallel and then the rheo in series with that right? haha my electronics knowledge is proving to be a lot better in theory than in practice.
Edited by Jacksonator36 - 10/27/15 at 7:31pm
post #5 of 17
Thread Starter 
Just to give you some more information in case it's needed, I'll be using about 5 case fans and want them all to run off of one dial. I've given up on having a display show the rpm/voltage cause people have suggested using an arduino as the easiest way and that's a bit much work and money for just an rpm monitor. But it would be good to be able to read the values still by connecting to the motherboard, but do i just connect any one header to the middle pin of a motherboard connector?
Also wondering, why a rheostat over a potentiometer?

Is there any international sites you would recommend for getting rheostats from? EDIT: woops, didn't check ebay, thanks @doyll
post #6 of 17
Fans in parallel, rheostat in series with +12V from PSU

Once you get beyond that things get complicated and expensive real fast.

Like this:
Fan controller that responds to 2 pwm input signals



Edited by billbartuska - 10/27/15 at 10:12pm
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post #7 of 17
Thread Starter 
Okay, seems simple enough, thanks! Is there anything I need to look out for when sourcing the rheostat such as resistance values etc other than the power handling capability? Also on your schematic, what is the unused wire usually for? Also does that mean i can use simple 3 pin connectors and don't need molex connections? Just want to save as much money as possible.

Also, when you first suggested a 25W rheostat, would you still think that is necessary with just 5 fans? They seem to usually only use about 1.5W max each so I would assume a 10W rheostat would be beefy enough. Is this not the case? Wouldn't the resistance of the rheostat get so high with a 25W one that it would only give a very small window of adjustability on the dial or am I thinking about it wrong?

Thanks very much for your help, you both seem well versed in these things so I really appreciate your help!
Edited by Jacksonator36 - 10/28/15 at 12:51am
post #8 of 17
Rheostats have basically, only two specs:
Power handling (just has to be more than the power usage - watts - of your combined fans).
If you want to do it "by the book" figure the fans draw 150% power at spinup.
Resistance (I think all you need is 1-6 ohms) I'll check the resistance of the Sidewinder rheostat when I'm at my workshop for you)

The fourth wire (usuallu bluie) is the PWM signal, you don't meed that because you won't be sending a PWM signal to the fans.

And no, power handling and resistance are independent. You could use a 1000 watt rheostat.

As an aside, there's an even easier way. You can switch the fans from being powered by the +12v rail to the +5v rail - but there would only be the two speeds, nothing continuously variable.

See this thread:
http://www.overclock.net/t/1521007/fan-controller/0_50#post_23057419



There's also a scheme to use the 5 and 12 volt rails to get 7 volts too.



As a second aside, there are also circuit boards that allow the fans to be powered by 12 volts directly from a PSU molex connector, but send the tachometer signal to a monitored and controlled fan header (CPU-Fan, or Chassi Fan) and that then ise the PWM wire to controll the speed of all the fans based on either the CPU or chassi temp.

http://www.amazon.com/Swiftech-8-Way-Splitter-Power-Connector/dp/B00IF6R4C8


Edited by billbartuska - 10/28/15 at 3:52am
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post #9 of 17
Old cars used rheostats to control heater fan speed. In fact, any car fan control would work. Just an idea.
post #10 of 17
Thread Starter 
Thanks once again! I think I'm going to stick with the idea of using a rheostat as I really want a nice shiny dial or two on my desk (with the added benefit of being functional).
So I don't think you answered one of my questions which was can I use three pinned fans which don't have molex connectors? I assume so, and the fan speed wire just needs to be attached to the middle connector of a 3 pin on the motherboard?
Sorry for all the questions, just don't have enough cash to screw too many things up tonguesmiley.gif
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