How come some fans have 3 wires and some have 2? The fan in question has no leds so its not for a led power. I am wondering because I am adding different ends to my fans to lengthen them and do not know where the extra one goes, or if it is even needed. The fan in question is a 120mm fan that came with my lian li v1000B. Thanks
The third wire (usually yellow) sends the RPM signal. Inside the fan's circutry, there is a little hall-effect sensor, and every time the magnet in the fan's hub goes past, it sends a little signal down the third wire. That's how motherboards read fans' speeds. There is not all that much use for them, except checking that a fan is working, and even then a temp sensor is better IMO.
the third (usually yellow) wire is for reporting fan speed back to a device. The fan will still run fine if you dont connect it.
The third cable, the yellow cable ISN'T ALWAYS for sensing RPM, sometimes it's a failure sensor. I've already worked with Nidec fans that had failure sensor instead of RPM sensor.
i guess on most newer mobo it could be considered both as a warning buzz or beep would be trip by an abnoraly low to no rpm
It can also be to attach one end of an external thermistor temperature sensor, as on my Papst temperature-controlled Variofan (other end of thermistor goes to ground). And with a Panaflo, a third wire may be for speed or for locked rotor detection. But most times, if it's yellow or white, it's the speed signal.
Nope, it doesn't represent RPM, it represents if the fan is locked, not spinning. The signal is continous and not pulses.
