How to connect 4 wire to 2 wire usb

[noblephantazm]

i have a 4 wire fan (blue, green, yellow and black) how do i connect it to a 2 wire usb cable (white and red)

 

[Paperdoc]

You may not want to. A standard 4-pin fan works on 12 VDC, A standard USB port can supply 5 VDC. Given that voltage, the fan MAY or may not start up. Once it is running, it will run at very low speed and push much less air than you expect. For large fans, the current draw MIGHT be a problem - a USB port can only supply 0.5 A max. A small 80 mm fan may use 0.2 amps or less, so that's OK, although a heavier current is required to start the fan. At decreased voltage, probably less current is used.

If you still want to do this, the tech info is this: the 4-pin fan's Black wire on Pin #1 is Ground, its Yellow wire on Pin #2 is for +12 VDC. The other two wires are not involved in power to the fan, so leave them unconnected. From a standard USB cable, its Black wire from Pin #4 is Ground, its Red wire from Pin #1 is +5 VDC. The other two wires in the USB cable are for signals - do NOT connect them to anything!. So, Black to Black, Red to Yellow.