Having trouble plugging in case fans.

I have a Rosewill Challenger computer case, which comes with three case fans. On of the fans I was able to connect directly into the motherboard in a Sys-Fan1 slot, but neither of the other fans have attachments on their cables that plug into the Sys-Fan2 slot, which is the same as Sys-Fan1. What they each have is one four pronged and one four holed rectangular plug. I tried to connect them to the power supply, by connecting them to a cable with similar plugins to the power supply. This cable also had a plugin for the Sys-Fan2 slot. When I tried to turn my computer on though, nothing happened. When I unplugged the fans from the power supply and mobo, my computer turned on fine.

Are my fans faulty, or did I wire wrong, and if I wired it wrong, how do I wire it correctly?
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  1. Best answer
    Wooops! You started out OK, but made a mistake later. For the two case fans that each have wires with 2 connectors on them, I think what you have are male (with pins) and female (with holes) 4-pin Molex connectors. The outputs from the PSU include (usually several) female versions of these on one or more sets of wires to be used as power supply points for peripherals like IDE drives, etc., and also fans. The intent of the wires on your fans is this: plug the male connector from the fan into the female connector from the PSU, thus providing power to that fan. Then use that fan's female connector as a daisy-chained output to plug in the second fan. This makes it possible to power two or more fans from only one PSU output, and that is quite OK - the power available on that PSU connector can easily supply several fans.

    But here's where your mistake came. You say the wires from the PSU that provide the 4-pin Molex power output connector "also had a plugin for the Sys-Fan2 slot". WRONG!!! That little 4-pin connector is a POWER OUTPUT connector from those same wires, used for smaller peripheral devices like a 3½" floppy disk drive. It should NEVER be plugged into a mobo SYS_FAN port. Doing that could cause a short circuit that damages the mobo port! So make sure you do NOT plug that into anything (assuming you don't have a floppy drive). Then your system can work properly.

    The case fans should be plugged into a 4-pin Molex output from the PSU. You should realize, however, that these fans connected that way can only run at full speed. The mobo cannot control power to those fans - it can only control the power and speed of a fan connected directly to a mobo SYS_FAN port.

    If you wish, you can buy an adapter to allow you to connect one of those fans to a 3-pin SYS_FAN port of the mobo, thus allowing you to control its speed. In fact, since the fans have those "daisy-chain" connectors on them, you could chain the second fan off the first, and have both controlled by the mobo port. This can only work, though, if the SYS_FAN port you plug into on the mobo operates in "3-pin fan mode". In that mode, fan speed is controlled by varying the DC voltage supplied to the fan. (4-pin fan control involves a different set of control signals and a different fan design to use them.) However, if you do this, you will not be able to measure the speed of these fans (even though you can control them) because these two fans do not have a way to generate a fan speed signal and send it back to the mobo for measurement. So if you do this, you might have to go into the BIOS Setup screens and tell it to ignore the fan speed measurement for that SYS_FAN port. Otherwise it may tell you constantly (and wrongly) that the fans on that port have failed because they are not sending back a speed reading.
  2. Best answer selected by seabasss95.
  3. Thank you for your help. I was really confused as to what I was doing wrong, but was also scared that my fans might have been faulty or something. I am really glad that it was just a mis-wiring. Thanks again, I really appreciate all of your help.
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