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Controlling 4-pin fans

By tylerplowright ยท 6 replies
May 23, 2010
  1. Hi guys,
    Have a bit of a problem/something I want to do with my computer. Am getting watercooling gear in about 2 weeks and as part of that getting three 120mm PWM 4pin fans to cool the radiator.

    What I want to do is hook all 3 up so that they can all be controlled by the same 4pin port on the motherboard (seeing as I only have one). Only need the speed sensor on one of the fans seeing as they will all be the same (or close enough). I know I can buy the harnesses for the fans, but don't really want to do that. Can solder and have spare male and female pins for the fans.

    If anyone can give me some advice/a design that would do this that would be great.
  2. dividebyzero

    dividebyzero trainee n00b Posts: 4,891   +1,262

    I think you have the choice of Y-splitters / PST cable or you can, like you say, modify one plug to accept the cables from multiple fans but connecting only one fan via the speed sensor, although this method that usually makes cable management hell on earth.
    Keep in mind that the ATX spec for the header is 1.0A/12v - some boards are happier with < ~750mA (mostly chipsets introduced prior to 2003-4 from my experience)
  3. tylerplowright

    tylerplowright TS Rookie Topic Starter

    Motherboard is Gigabyte P35-DS3P. Not quite sure what the motherboard would want. But I'm planning to hook it up to the cpu fan socket. Fans i'm buying are Nexus Real Silent PWM 120mm Fans

    So would this work IF I wired all the positive, negative and PWM wires together and only took one of the speed sensors and put that into the plug to go into the board? Would I need to wire together the other speed sensors or could those cables merely but cut off?

    Thanks again
  4. CMH

    CMH TechSpot Chancellor Posts: 2,039   +9

    Don't really need the speed sensors if you're only going to monitor 1 fan.

    In fact, you're basically using the other fans in a 2-pin configuration this way. No need to physically cut the other wires off the fans, just don't connect them (or if you want, cut them on the splitter).
  5. dividebyzero

    dividebyzero trainee n00b Posts: 4,891   +1,262

    IF you're daisy-chaining the fans then yes, speed sensor from Fan #1 to motherboard fan header (i.e. all four pins). Fans #2 and #3 connect without the speed sensor wire. As CMH pointed out, you don't need to cut anything-just release the speed sensor wire from the plug block. I usually thread the bared end of surplus wired with a small length of heatshrink tubing, apply a little heat and viola! -electrical tape would do as well. You never know when you might need to reconfigure your setup.
    This setup should keep all three fans running in unison, although I would point out that there is some lag between the PWM sensor being dialled up by the board and you having the coolant temp drop.
    Personally I would look at ultra low noise (ULN) fans running at moderate rpm continuously (i.e Noctua NF-S12B), or a stock higher rpm/louder fan/s with a 7 volt mod (quick method or here) , or my preferred method:
    Put a 10 ohm 2 watt resistor in series with the +12volt wire. Cut the wire. Strip the ends, wrap the two stripped ends, one on each side of the resistor close to the resistor body, cut away the excess resistor leads, solder, tape (or heatshrink), this will give a much quieter 10 volt (approx) fan.

    I've including all the options for others who might view the thread and need some ideas along the same lines.
  6. CMH

    CMH TechSpot Chancellor Posts: 2,039   +9

    I'm always very wary of using the 7 volt mod. Cheaper PSUs just aren't built to handle current like that on the +5V rail, and failure can be catastrophic.

    Then again, haven't ever heard of anyone running into problems, so just be careful.

    Back to the topic.

    Google will quickly tell you which leads are to power the fan, so just wire those together, and the last fan can be wired to the PWM. Are you planning to software control all the fans, or are you using the PWM pin just as a monitoring tool? I'm not quite sure how PWM fans are controlled by the motherboard (ie, if they need the extra pins to do so). As far as I know, they're all just sensor wires.
  7. tylerplowright

    tylerplowright TS Rookie Topic Starter

    Fans will be controlled by the motherboard through a 4pin slot. Am pretty sure the PWM pin is the one that actually controls it.

    Yes I know there will be a bit of lag, but, they will be running at a high enough speed that this shouldn't be too much of a problem, more of a failsafe.
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