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Connect 3 pwm fans to motherboard ?

Last response: in Components
October 15, 2010 6:31:56 AM

So i have a noctua NH D14 and i want to add another fan so a total of 2X 120mm & 1X 140mm in the midddle what is the best way to accomplish this? with this?
will the mobo controll the speed of the 3fans?
my mobo is gigabyte X58-UD5
a b ) Power supply
a b V Motherboard
October 15, 2010 7:19:40 AM

So you want to be able to control all three of the fans and there speed.
First of all if you use the connector, no the mobo wont control the speed of the fans.
Because that connector mates with a spare free molex straight from the power supply.

So no power Modulation= all three fans at full speed.
Now i had a look at the board. and it looks like you have plenty of headers on it to connect the three four pin mini plug.

1. cpu fan for one.
2. and two system fans for the two 120mm

All the fans/ and there speed can be controled by the mobo then.
Short of that buy a fan unit to fit in the cd bay and connect the fans that way.

Ok pest1320.
a b ) Power supply
a b V Motherboard
October 15, 2010 4:10:55 PM


The problem with that approach though is all 3 fans may be running at different speeds if the motherboard manages them from different headers.

If all 3 fans you're using/want to use are 4-pin PWM fans then I recommend connecting all 3 of them to the CPU fan header using this:

All 3 fans will then be in sync with each other based on what the motherboard controls.

Alternatively, run them off a fan controller, but to be honest I'd just run the fans full tilt - those used on Noctuas are very quiet even at full speed so there's no real point in slowing them down.
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a b ) Power supply
a b V Motherboard
October 15, 2010 4:45:14 PM

I'm a little confused because the links in the first and third posts are the same. But the answer is YES. I disagree with Shaun O and here's why: That adapter IS cleverly designed to do exactly what it promises. It distributes power and the PWM control signal to all fans, plus feeds ONE fan speed signal back to the mobo port. The "problem" it addresses successfully is that most mobo 4-pin fan ports cannot deliver enough current to power more than two fans simultaneously, especially at start-up time when fan current draw is heaviest. Instead it uses a 4-pin Molex connector as the power source for the three fans, and that source can provide much higher total current as needed. BUT the adapter still provides to each fan the same PWM control signal, so all of them can use it. The circuits located in each 4-pin PWM fan draw very little current from the PWM signal line so there is no real "problem" doing this part. And finally, having only one of the three fans' speed signals sent back to the mobo is the right way. A speed signal is a series of pulses - 2 per revolution - generated by the fan and sent to the mobo for counting. If you feed more than one such pulse train back on the same line, the mobo result will be quite wrong! The only limit by doing it this way is that the other two fans' speeds will never be known, which is OK.

Now, I will point out one thing to recognize as the adapter is installed. If I understand correctly, OP has one CPU fan already connected to the CPU_FAN port on the mobo and that is completely not part of the current discussion. OP then has two existing 4-pin CASE fans operating and wants to add a third in a manner that has ALL of them controlled (speed-wise) by ONE mobo 4-pin SYS_FAN port. This adapter will do that job perfectly. BUT recognize that the connector that goes to the mobo port may be labeled to plug into the "CPU_FAN" port whereas you really want it to plug into that SYS_FAN port. Likewise, ONE of the three outputs is labeled for powering the CPU fan, but should NOT be doing that - OP's CPU fan already is connected as it should be, to the CPU_FAN mobo port. This output is merely connected to one of the three case fans OP wants to use.

Please note: I made an assumption above that may not be correct: that OP really wants to be using 4 fans - one on the CPU cooler connected to the CPU_FAN port, plus three as case fans controlled separately. If, instead, OP means that he / she want to use one CPU fan plus TWO case fans, all controlled by the same mobo 4-pin fan port, that's a different story and is exactly what the adapter is for. You install it exactly as the various wiring labels say. BUT now there is a different limit: the two case fans connected this way will be governed by the CPU's measured internal temperature, and not by the mobo temperature. You need to recognize that most systems have TWO separate temperature measurement and control loops. ONE of them uses a temp sensor built into the CPU and controls cooling of the CPU only (under normal circumstances). The second uses a temp sensor built into the mobo and controls Case Fan(s) to keep the mobo at the right temperature. Using the CPU cooling controller for both jobs is not quite right, although I suppose there is likely to be a reasonably good correlation between CPU temperature and mobo cooling requirements.

Best solution

a b ) Power supply
a b V Motherboard
October 15, 2010 5:14:42 PM

Well, in my haste I never even noticed the OP's link!

Advice remains as I think it's pretty clear the OP is talking about loading up that triple fan Noctua monster ("2x 120mm and 1x 140mm in the middle").

I have just noticed two things though: first is 140mm fans spin slower than 120mm fans, so PWM control on all 3 fans might confuse them, and second NONE of Noctua's fans are PWM, so this is a pretty redundant convo now!

So OP: if you want PWM control then load up with 3 4-pin PWN fans (Akasa Apache Blacks are nice). Otherwise you can link everything into a fan controller and do things that way, or run everything full tilt like (I believe) Noctuas are supposed to do anyway.
October 15, 2010 6:42:29 PM

Gotcha so since the noctua fans are not PWM (idiot for that one).I do have a fan controller and thats what i was going to do in the first place but my buddy told me it should to be controlled by the mobo,Now since they are not PWM they cannot be controlled by the mobo.I will link the 3 together into my Lamptron FC5 ver.2 30W per channel2 like below...
so now i can have
1.intake channel1
2.noctua 3 fans channel2 (and leave them full speed)
3.2top exaust channel3
4.main exaust channel4.(ill leave full speed for now unless get higher rpm fan later)
Seem okay?
Thanks guys i really appreciate the help now i def. know the meaning of PWM (Pulse Width Modulation)
October 26, 2010 12:39:36 AM

Best answer selected by pest1320.
a b ) Power supply
a b V Motherboard
October 27, 2010 9:35:16 AM

Your buddy's only got half the story.

You can let the motherboard control the speed of the fans just so you don't have to worry about it yourself, but it's not 100% required that the motherboard does it.

And as you've seen, some fans don't have such control.

Incidentally, certain motherboards can control certain 3-pin fans by old-school voltage changes through a header, it's just that PWM is more effective.

Happy to help though - enjoy the rig!