Questions about fan and fan hub speeds.

[iseeu1001]

So I bought an Ml140 pro led but if I want to put that in my computer I need a fan hub so I bought a silverstone 1 to 8 pwm. Now I was thinking should I just have gotten an NZXT sentry 3 touch screen fan controller? The think that stopped me from getting it was that it did not have a 4th pin for the fan so is my ml140 useless then a Corsair Air Series AF140 Quiet Edition 140mm. How does the fan controller work on the nzxt if the fan plugs only have 3 pins?

 

[Paperdoc]

Almost all 4-pin fans CAN be powered and controlled for speed by a 3-pin fan header that uses Voltage Control Mode. Technically it is not as good as using proper PWM Mode control but it does work.

For a 4-pin fans, the signal on the mobo headers are: Pin #1 Ground, Pin #2 +12 VDC (fixed), Pin #3 Speed Pulse signal, Pin #4 PWM Signal. The speed signal on Pin #3 is generated in the fan motor and sent back to the mobo on this line. Although it is NOT used for fan speed control, it is used to monitor for fan failure and to display fan speed for you. Inside the fan there's a small circuit with a chip that applies that PWM signal to the incoming +12 VDC supply to modify the flow of power through the fan motor windings, thus altering its speed. This is called PWM Mode of speed control.

For older style 3-pin fans the signals are the same on Pins 1 and 3. There is no Pin #4 so the fan gets no PWM signal, and it does not have a chip to use it, anyway. Instead, the DC supply on Pin#2 varies from +12 VDC (max for full speed) down to about +5 VDC for minimum speed. This is called Voltage Control Mode (aka DC Mode) of speed control.

When you plug a 4-pin fan into a 3-pin header, it gets no PWM signal to use, so it cannot modify the power supply from Pin #2. BUT that pin's voltage varies, and that accomplishes speed control. This is part of the backwards compatibility of the 4-pin fan design.

Personally, I think you chose the right way. Using a Splitter or a Hub for 4-pin fans puts all those fans under automatic control by the mobo, based on a temperature sensor built into the mobo. A third-party Fan Controller module mounted in the front of your case does NOT do that. None of those units have access to the mobo temperature sensor. Most such units make no attempt to give you automatic fan speed control based on temperature measured anywhere. They make YOU the temperature controller. YOU must decide (on what basis?) what fan speed to run, and when to change it.