3-pin Fan to 4-pin Header

[TrazKing]

Can the 3-pin fans which come with the Corsair 300R case can be used on the 4-pin fan header on the GA-Z97X-SLI mobo? I noticed that the SYS_FAN1/2/3 pinout on the mobo indicates 1=GND, 2=+12V/SpdCntrl, 3=Sense, 4=VCC. Seems to me that the fan would need both GND and VCC so it would not be possible to use a 3-pin fan with this header. Am I correct?

Here are links to the items in question...
https://pcpartpicker.com/part/gigabyte-motherboard-gaz97xsli
https://pcpartpicker.com/part/corsair-case-300r

Thanks!

 

[Guest]

3-pin and 4-pin connectors are inter-compatible. They can be used however you want.

 

[TrazKing]

3-pin and 4-pin connectors are inter-compatible. They can be used however you want.

I'm just concerned that the VCC connection will be left off. Doesn't the fan need both GND and VCC? Does pin 2 (+12V/SpdCntrl) supply the necessary pos voltage for the fan then? Isn't VCC 5V? Confused! I don't want to damage any mobo components and I'm ready to try my first power up. I'd like a warm fuzzy feeling before hitting that switch.

 

[Guest]

You can try to read this for an understanding: http://en.wikipedia.org/wiki/Pulse-width_modulation
but I can tell you that there are no worries.

 

[TrazKing]

You can try to read this for an understanding: http://en.wikipedia.org/wiki/Pulse-width_modulation
but I can tell you that there are no worries.

Thanks for the feedback. I''l take your word for it and hope all goes well. I'm now ready to push the button for the first time... gulp!

Well, I just power up for the first time with the 3-pin fan connectors attached to the 4-pin headers on the mobo. You were correct. All fans are working! So sweet to see the flash screen for the first time with all the fans turning nice and quite. Thanks for the encouragement. This forum is great!

 

[burdenbound]

The fourth pin is for controlling fan speed, so a three pin fan just doesn't have this feature.
https://www.google.com/search?q=4+pin+pc+fan+pinout&es_sm=119&tbm=isch&tbo=u&source=univ&sa=X&ei=jaPsVNufAtXfoATO2YL4Dg&ved=0CCwQsAQ&biw=1280&bih=1318#imgdii=_&imgrc=sMfysLf00S8lrM%253A%3BxZ1mXtGED-98qM%3Bhttp%253A%252F%252Fwww.overclockers.com%252Fforums%252Fattachment.php%253Fattachmentid%253D92908%2526d%253D1300219923%3Bhttp%253A%252F%252Fwww.tomshardware.com%252Fanswers%252Fid-2137887%252Fcas-fan-pin.html%3B370%3B437

 

[hwc1954]

Here is Noctua's illustration for fan pins:

The first three wires are the same, in order:

GROUND
+12 VOLTS
RPM SPEED SIGNAL

There are tabs on the fan headers that prevent you from mis-alignment. Either a 3-pin fan or a 4-pin fan can match up with a 4-pin header and the connections will be the same.

The fourth wire on a true PWM 4-pin header is the speed control wire. It uses a PWM signal (series of on/off pulses) to tell the fan how fast to turn.

A 3-pin fan connected to a PWM header will typically turn at full speed since it is connected to +12V and there is no PWM signal to tell it to run slower.

ONE EXCEPTION: many motherboards use 3-pin headers with variable voltage on the +12V pin. In other words, they can control the speed of a 3-pin fan by raising and lowering the 2nd pin between +5V and +12V. Dell uses this configuration for their chassis fan headers, which have automatic speed control.

SECOND EXCEPTION: Some motherboards use a "fake" 4-pin header that does not have a PWM signal on the fourth wire, but a constant +5V signal. A true PWM fan connected to this header will run at 100% speed. A 3-pin fan connected to this header will run at full speed. But, either kind of fan connected to this header can have variable speed if the second pin (the +12V pin) has variable voltage. Many recent high end aftermarket motherboards have this configuration for chassis fan headers.

Honestly, what needs to happen is for everyone to move to true 4-pin PWM headers and fans for all applications.

 

[hwc1954]

I noticed that the SYS_FAN1/2/3 pinout on the mobo indicates
1=GND
2=+12V/SpdCntr
3=Sense
4=VCC.

One of the problems in understanding all this is that the Chinese manufacturers do a poor job of explaining their products in the manuals. The language used is often confusing and requires interpretation. My best reading of your manual's language is:

1=GND
2=Variable +12V (the SPD CNTL implies variable voltage to change the speed of the fan)
3=Sense means RPM speed signal (the MB can "sense" the speed of the fan)
4=constant +5V

This would be one of the "fake" 4-pin headers I described above, but the good kind on better motherboards that has variable voltage on the +12V pin so you can have motherboard/bios controlled speed, i.e. variable speed based on CPU temp.

This is a ideal kind of header for use with a 3-pin fan. Most PWM 4-pin fans will work fine with it, too (although there are some PWM fans that don't like variable voltage).