Sense pin in Sys_Fan

Gaiger · September 25, 2020

What is the general purpose of that pin. I got my Phantek Fan Splitter 4 Pin and one of the split got no 3rd pin, I check my motherboard manuel
and it says that sense pin.

Thanks for responding my post.

BlueChinchillaEatingDorito · September 25, 2020

23 minutes ago, Gaiger said:

What is the general purpose of that pin. I got my Phantek Fan Splitter 4 Pin and one of the split got no 3rd pin, I check my motherboard manuel
and it says that sense pin.

Thanks for responding my post.

The fourth pin provides PWM control. For a fan, this just allows the motherboard to better control the speed of which that fan operates. That way you can have it run at low RPMs when the system is at idle or doing less intensive tasks, and at high RPMs when you're gaming or running very intensive tasks. This ensures your system is as quiet as possible while also maintaining good thermals.

fordy_rounds · September 25, 2020

27 minutes ago, Gaiger said:

What is the general purpose of that pin. I got my Phantek Fan Splitter 4 Pin and one of the split got no 3rd pin, I check my motherboard manuel
and it says that sense pin.

Thanks for responding my post.

This is pretty normal for 4-pin fan splitters. The pins are, in order: ground, 12V*, sense, and PWM. The sense pin is actually for your fan to send a signal back to the motherboard about how fast the fan is spinning. When your fan control software gives you an RPM, that's how it knows. However, because it's from the fan to the motherboard, it would be a problem if two fans tried to connect to it at the same time. They'd end up just giving garbage information to the MB. So, the splitter has it pinned through to what you might call a "master" fan; only this fan gets to report its RPM. The other fan(s) on the splitter don't get to report their speed, but they can still be controlled by PWM (which is connected to all the fans, on pin 4).

Note, too, that I put an asterisk on the 12V pin. Some fans don't have a PWM connector; these have to be controlled by voltage control instead, which is that, rather than providing a steady 12V and controlling speed with a separate signal, the MB actually changes the voltage on the 12V line to be less than 12V in order to run at a slower speed. Note, though, that the fan can still send its RPM over pin 3 (unless it's on the disconnected side of a splitter). If you mix PWM (4-pin) and Voltage (3-pin) fans on a splitter, the 3-pin fans will run at full-blast all the time. That's not recommended.

LogicalDrm · September 26, 2020

Sense reports fan RPM to mobo. Mobo header can see only single fans RPM at the time, so all splitters have that in only one of them connected. As said, controlling still works, be it PWM or DC. Software use that sense to give control options.