Do 2 wire case fans have sensors?

westy · Post by **westy** » Fri Dec 12, 2014 6:20 pm

Just curious if the case fans with a black and a red wire (2 wires total) will have a speed sensor.

Thanks!

RaisinCain · Post by **RaisinCain** » Fri Dec 12, 2014 6:27 pm

Your motherboard should adjust the speed according to your temps.

westy · Post by **westy** » Fri Dec 12, 2014 6:36 pm

What I'm wondering is if the connections on my motherboard will "read" the (2 wire) fan speed if connection to the headers on the mobo.

Easto · Post by **Easto** » Fri Dec 12, 2014 9:49 pm

I do not believe so. The 2 pins should be power only.

RaisinCain · Post by **RaisinCain** » Sat Dec 13, 2014 11:11 am

Yeah come to think of it, they would need to be 3 pin(wire).

Post by **Philip** » Sat Dec 13, 2014 7:34 pm

Two wires are power only, the motherboard can't read their state as already mentioned above. Most likely it will not change/control their speed.

However, even with two wires the speed of a fan can be reduced by varying voltage to it.

Fans run on 12v, however, they will start with as little as 5-7 volts at a slow speed, and varying voltage up to 12 will speed them up. This is often used with inline fan speed regulators (they just put a resistor/potentiometer to reduce the 12v and vary speed). There are others that simply use the different pins from a simple 4-pin power connector (yellow-red-black-black)... Yellow is 12v, Red is 5v, black is ground:
Ground+5v gives you very slow speed
5v+12v (7v difference) gives you medium speed
Ground+12v for full speed.
All three of those speeds can be achieved with a simple 4-pin power connector.

In addition, the fan itself can have temperature sensor and speed control on it, that is regardless/independent of a third pin (remote control).

I hope this helps some

westy · Post by **westy** » Fri Jan 09, 2015 10:21 pm

I was just wondering if I hooked them up to the fan leads on my mobo if they'd show the RPM of the fan. Right now, I have them connected to a PS cable. Guess not....