cpu fan /computer fans???

Discussion in 'Computing and Networks' started by Mathematics!, Nov 15, 2009.

  1. Mathematics!

    Thread Starter Senior Member

    Jul 21, 2008
    I have an old computer cpu fan that I thought I could turn on by connecting the red wire to 12 volt dc supply and black wire to ground.

    To my suprise I couldn't get it to move at all.

    Their is 3 wires on this fan
    red = VCC
    black = ground
    white = s = signal RPM

    I even tried connecting white to the 12volt supply and removing it then connecting it ....etc nothing moved still?

    When I plugged it back into the computers mobo and started the mobo/computer it spun like normally.
    WTF ???

    The fan
    model is 0925-12HBTA DC 12volt 0.60 A Brushless DC FAN by JMC DATECH

    Question 2
    I have another cpu fan that is the same as that one but with 0.80 A.
    So I thought I could substitute the 0.6 A fan for the 0.80 A fan on the mobo. Both have the same connector and fit fine on the mobo and both use 12 volt dc.

    Didn't think the 0.20 Amps would make a big difference or at least I would see some spin or something. To much my suprise I saw nothing got to bios "post" beeps and a screen saying the cpu fan could not be detected.

    So are mobo so current specific if so are their any standards on what a mobo current must be. I just find it hard to believe that 0.2 amps makes that much of a difference thought I would see something spin at some rate ?

    Is their any fan standard for what a fan can have for amps or something or what mobo it can be used on? Because you can pickup fans at radioshack/bestbuy ,...etc and most people won't be looking for amps when buying they just buy ?
    I do admit these computers/fans where bought in 2000 so maybe they have a standard now anybody know?

    This all got me thinking if I ever have to replace a computers fan I have to look at the amps it runs on and know what the mobo amps are. All computers I know run on 12 volt dc but some of them run on more amps then others. So I would assume that fans are mobo specific as well as memory ,...etc never thought about the fan that way.

    Guess the small circuitary of the fan amps needs to corrospond to the amps of the mobo.

    Anybody that knows more please let me know.

    It all sounds pretty sketchy that you have to know the computer mobo amps this is why I think their must be a standard now. Unless they are figuring out the amps of a mobo by the power of the power supply divide by the 12 volts = current
    Thanks for any input or clarity
    Last edited: Nov 15, 2009
  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    I've not had problems connecting fans, Yellow from the power supply is +12V, red is +5V.

    The white/sensing wire is simply pulses out for each RPM, the motherboard will throw an error if there isn't a pulse stream of a minimum frequency (selected in BIOS on Aftermarket ASUS boards).

    They are outrunner 3 phase brushless DC motors with all controller circuitry on the stator, so are slightly more picky on voltage, usually 7-14V to run. Too low and it doesn't get the circuit going.
  3. Wendy


    Mar 24, 2008
    Fans from a user standpoint have simplified a lot. They are all brushless (standard) and use solid state circuits to drive them (a specialty 8 pin chip can usually be found in the innards, sequencing 6 coils from a simple RC oscillator).

    The only thing everyone needs to be aware of is if you cause them to spin up (usually via air from a can or compressor) they will burn out in a heartbeat. Those coils feed the back EMF into the chip in exactly the wrong way.
    PackratKing likes this.
  4. BMorse

    AAC Fanatic!

    Sep 26, 2009
    I have worked with computers for a long time and fan/power is one thing that never really come up.... Usually any CPU cooling fan with the 3 pin connector would work even on newer mobo's with the 4 pin connector, I have even had the 2 pin fans from old AT style PC's to work with the 3 pin connector on the mobo's....... I know some mobo's, you will have to set the "Smart Fan" features, depending on the type of fan, (the system normally PW Modulates the fans to speed them up and slow them down depending on mobo temps.).....

    My .02
  5. Mathematics!

    Thread Starter Senior Member

    Jul 21, 2008
    I understand what you are saying but nothing is working to spin these fans other then plugging them into the computer and starting the computer then it works fine.

    I was think it could be easily started with out the computer at least at some speed?


    And no the fans cann't be interchanged unless their is some bios setting used to set the amps of the fan in use or something which I don't think their is?

    thanks for the input