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Question about 3-pin speed-controlled fans?

Discussion in 'Tech Support' started by Sparrowhawk, 15 Dec 2006.

  1. Sparrowhawk

    Sparrowhawk Wetsander

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    Hi-
    My question is, with the three-pin speed control fans, I know the Red, black, and yellow wires are +12v, GND, and speed-sensing respectively, but my question is if you attach two speed controlled fans to the same yellow wire, will they run in tandem at the same speed? Or will they screw up somehow? :wallbash:
     
  2. tolis86

    tolis86 New Member

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    if the connection is parallel they will both be connected to 12, 7 of 5 vlots(depending on how you make the connection) so they will work independantly.if yoy connect the black from the first one to the red o the second and the black of the second to the psus black then the 2nd one will not "take" 12 volts and so it will work in lower speed. but why do that?

    if both red wires of both fans are connected to psus yellow they will work both at 12 volts. they will run to same speed if you set them to same speed and if they are identicall ofcourse...
     
  3. Spaceraver

    Spaceraver Ultralurker

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    what you're asking is if you connect both yellow wires coming from the fan together they will run at the same spped right??
    It doesnt work that way im afraid, it only tells the sensor chip on mobo/ fan controller that it runs..
    Or if you have MBM or Speedfan installed it will show the rpm output..
    You can't make them sync if thats what you are trying to achieve.
    Also, if you connect both yellow lines together, best case: they will make the sensor chip confused.. Worst case. Something goes poof, and that will be the end of your system
     
  4. Sparrowhawk

    Sparrowhawk Wetsander

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    Ah, thanks Space. Yeah, that's what I meant.
     
  5. M4RTIN

    M4RTIN New Member

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    bit of a hijack but is that why the intels have four wires then, so it has an exact speed
     
  6. Ramble

    Ramble Ginger Nut

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    Having a look at some obscure intel pinout sheet it has four wires because one is for sensing and one is for control. I don't actually know why you need two wires for this however.
     
  7. Krikkit

    Krikkit All glory to the hypnotoad! Super Moderator

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    I don't know why you need to do that at all - just a simple voltage drop works just fine with a decent sensor.

    You can run 2 fans in parallel, the sensing works just fine too. (Although I have two identical fans). All it is is a small pulse sent down the wire afaik. Give it a try.
     
  8. Firehed

    Firehed Why not? I own a domain to match.

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    You don't get odd speed readings with joined sense wires? Or are you using a splitter that just leaves out one of the senses, as most 3-pin splitters do?

    It certainly shouldn't cause damage though, just weird readings at the worst. It's a signal line, not power.
     
  9. ChromeX

    ChromeX Active Member

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    my guess is that the sensing has the same function as the yellow wire on a standard 3-pin fan header (make sure the fan is spinning) and the control wire is used so that when the fan is cpu is cool is reduces the fan speed to lower noise and vice versa. Just a guess though.

    EDIT: Yup, the control wire has a PWM singal sent to it in order to control the fan speed. http://www.formfactors.org/developer\specs\REV1_2_Public.pdf
     
  10. Krikkit

    Krikkit All glory to the hypnotoad! Super Moderator

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    Nope, works just fine. The two sense wires are both connected. If you do get odd readings, you can use MBM5 to alter the divisions for the fans if you do get odd ones anyway, so it's all good... :D
     
  11. cpemma

    cpemma Ecky thump

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    The new 4-wire fans have an always-on 12V supply for the electronics and a pulsed (PWM) 12V supply controlled by the motherboard hardware monitoring chipset going to the motor coils for speed control. Plus a common ground and a speed wire. The chipset doesn't set a certain fan speed in RPM, it just speeds the fan up as the temperature sensor gets warmer, slows it down as things get cooler.

    Joining two speed sensor wires together just confuses the speed monitor. At best it will add the two speeds, but it's more likely to give a garbage reading. Just use 1 sensor per fan header.
     

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