Curious as to how fan headers work

[Sonefiler]

Hey guys. 

 

I'm trying to figure out how fan headers work. From what I've researched online, I understand that a 3-pin fan header consists of +12V/5V, Ground. and the Tachometric signal. I also understand that the tachometric signal isn't necessary, and if it isn't used, the fan will just run at full speed. 

 

My question is: If I only used two pins, would I be able to still turn off the fan? I know that I wouldn't be able to control the RPM, I just want to know if I could shut it off altogether. 

 

The reason is that I want to use the fan header with a relay switch and essentially use the fan header as GPI/O. 

 

Thanks guys!

[Lefteh]

As long as it doesn't use the 5vsb (5vsb is always on as long as the power supply is plunged in and the switch in the back is on this is what allows some parts of motherboard to glow and the ability to turn on the PC)  which spoilers it doesnt your fine.

here a 4 pin

 

3 pin

[Sonefiler]

1 minute ago, Lefteh said:

As long as it doesn't use the 5vsb (5vsb is always on as long as the power supply is plunged in and the switch in the back is on this is what allows some parts of motherboard to glow and the ability to turn on the PC)  which spoilers it doesnt your fine.

here a 4 pin

 

4 pin

Awesome, thank you so much!

[Firewrath9]

yeah, fan speed is voltage controlled, if you run it at 9v, it'll run a bit slower, at 0v it'll not move

[Sonefiler]

Just now, Firewrath9 said:

yeah, fan speed is voltage controlled, if you run it at 9v, it'll run a bit slower, at 0v it'll not move

so my plan to use the fan port as GPIO with Speedfan should work, right?

[Lefteh]

14 minutes ago, Sonefiler said:

so my plan to use the fan port as GPIO with Speedfan should work, right?

do you know how much current a fan draws? Like .1 to .3 Amps Im afraid your going to need somthing that the GPIO pin can control because directly im afraid the pin will burn, and at low voltages the fan pulls even more amps( 1v to 3v because the fan doesn't spin it just tries).

 

edit:

Crap did i just miss read lol i was thinking you were hooking up a arduino or rasberry pi lol

[Sonefiler]

1 minute ago, Lefteh said:

do you know how much current a fan draws? Like .1 to .3 Amps Im afraid your going to need somthing that the GPIO pin can control because directly im afraid the pin will burn, and at low voltages the fan pulls even more amps( 1v to 3v because the fan doesn't spin it just tries).

 

edit:

Crap did i just miss read lol

I'm not sure if you misread. I could be getting something super wrong since I'm not very good with electronics and stuff, but my plan is to toggle a relay switch using the fan header

[Lefteh]

Uh well normally to control the speed of a fan you use a PWM( giving a duty cycle say 50% on at 12v and 0v would give a speed of 50% on the fan) signal, are you just trying to turn the fan off outright?

[Sonefiler]

1 hour ago, Lefteh said:

Uh well normally to control the speed of a fan you use a PWM( giving a duty cycle say 50% on at 12v and 0v would give a speed of 50% on the fan) signal, are you just trying to turn the fan off outright?

I want to be able to just switch between the "fan" being 100% on and 100% off, on the fly.

[Lefteh]

27 minutes ago, Sonefiler said:

I want to be able to just switch between the "fan" being 100% on and 100% off, on the fly.

then ya it should work

[Sonefiler]

I got it working!

 

Just wanted to let people know how I got this working, in case anybody in the future wanted to do this:

 

To hook up the relay switch, I wired two Molex connector pins, the +12V and a Ground pin (seems like it depends on the power supply you're using as to which wire corresponds to which), to the relay switch. I wired the +12V (Middle pin) from the fan header as the actual switching signal. Then I used motherboard fan curve adjustments to make the fan stay at 0RPM until 45 degrees, then have it go to full throttle!