by AlbertoGP » Thu Jul 10, 2014 4:49 pm
Normally, the black wire is "Ground", the red wire is "+12V", and the yellow wire is the tachometer signal: two or four pulses per turn of the fan, to tell the mainboard how fast it is spinning.
To cool the Parallella, you need to plug only the ground and +12V wires: the fan will run a the speed proportional to the voltage, with the standard RPM if you supply the standard 12V for which this fan is rated.
If you give it less volts, it'll spin slower. That's how a computer's motherboard or fan controller can make it adapt to the temperature inside the computer.
I've looked at the specifications for that fan () and it does not indicate the starting voltage: that's the minimum voltage at which the fan will start spinning, which will be lower than the standard 12V. Some 12V fans have a starting voltage of 4.5 and can work with the 5V you can get from the Parallella board, others require for instance 8V and will need their own power supply.
In your case you'll probably have to try it out with a 5V power source.
I've put what I found out trying different fans here:
Before getting those small fans I used a 92mm 12V case fan I had at hand: I tried to power it with 5V and it worked very well, but other two 12V fans I tried at the time did not start up with 5V.
