I rescued a box of brand new 'Nidec UltraFlo V60E12BS1A7-09A032 12VDC 2.45A' fans from being thrown away and of course I haven't got the datasheet for them. The closest matching datasheet is here: http://www.nidecamerica.com/fanpdfs/c2008_1314.pdf but I suspect mine are custom made for HP.
It has four wires:
- black => GND
- red => +12VDC
- yellow => I thought this is tacho open collector to GND, but I can't measure any frequency on it both with and without a 10k pull up to +12V, it is near 0V all the time. On top of that the wire is as thick as both black and red, whereas the green wire is clearly thinner.
- green => Seems enable (0V) / disable (12V or anywhere in between)
Does anyone know the proper specs for the yellow and green wires on these fans?