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Quick fan connection question!

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April 12, 2010 5:46:24 AM

Hey all,
I am building my first PC and am to the point of hooking up the case fans. I am hooking up the three fans in my CM 690ii Advanced case and wanted to hook them up directly to my Gigabyte X58A UD3R mobo which has one four pin Fan connector which the manual lists as having speed control, and two three pin which don't mention speed control, but just list Sense capability.

My fans all have very small connectors (three pin female), but have a connector added to this that have both a male and female molex. I just need to disconnect the adaptor that has the molex connections, and plug directly into the fan headers on the mobo right? Please verify.

Also, do I really only get fan control with the one fan connector I mention above? If that's the case, I thought I would control the front fan and hook up the back and top exhaust fans to the other ports. Thoughts?
a b ) Power supply
April 12, 2010 3:28:45 PM

Dre325 said:
My fans all have very small connectors (three pin female), but have a connector added to this that have both a male and female molex. I just need to disconnect the adaptor that has the molex connections, and plug directly into the fan headers on the mobo right? Please verify.


Probably. Try it and find out. You can't hurt anything.

Dre325 said:
Also, do I really only get fan control with the one fan connector I mention above? If that's the case, I thought I would control the front fan and hook up the back and top exhaust fans to the other ports. Thoughts?

Have you already hooked up the CPU fan? If not, the four pin connector is where it should go.
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April 12, 2010 3:40:36 PM

I've already hooked up the CPU fan. It has a dedicated fan port.

I'm starting to get the feeling that not a lot of people hook up their case fans to their motherboard. I thought this would be a simple question to answer.
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Best solution

a b ) Power supply
April 12, 2010 5:33:16 PM

Fans are not very complicated, and you're already most of the way there.

First, you are right to connect the CPU cooling fan to the mobo CPU_FAN pinout. That is really the only good way to do it. That allows the mobo to monitor the CPU fan in case of failure, and to control its speed according to a temperature sensor inside the CPU case. You would not want another fan connected to this pinout.

Next, some general rules on cooling fan connections. The older style uses 3 pins on the male mobo pinout and a matching 3-hole female connector on the wires from the fan. The color code is black for Ground, red for +12 VDC (varies to achieve fan speed control), and yellow for a pulse signal sent by the fan back to the mobo for speed measurement. The newer 4-pin system uses the same three lines plus a fourth for PWM signal. It uses a different color coding system, and in PWM mode the +12 VDC line is always at that voltage - fan speed is actually controlled by a little module inside the fan that uses the PWM signal to control flow of current to the motor.

With clever design it is arranged that any 4-pin male mobo pinout can accept either a 3-pin or a 4-pin connector from a fan. In each case the first three lines are the same. Physically there is only one way to plug in the connector, no matter which. The only thing a user needs to do is in setting up how the fan speed is controlled. Within the BIOS Setup configuration spot for a 4-pin mobo pinout for a fan, you need to tell it whether it is feeding a PWM (4-pin) fan or a 3-pin fan. Then the mobo can arrange to send the correct speed control signals out the port.

If you have a 3-pin mobo pinout for a fan, you can ONLY use a 3-pin fan - no 4-pin fan can work from that.

Some mobos have a pinout labeled PWR_FAN. It is used for a special connector that looks like a 3-pin connector from a fan, but comes directly out of the PSU. It intent is NOT to control the PSU's internal fan speed - that is done within the PSU itself. But IF your PSU has this connector, it provides the PSU fan's speed signal to the mobo for display. Many PSU's do not have such a signal output. I have seen posters here say that this mobo pinout actually can accommodate a normal 3-pin case cooling fan, but it will always run at full speed.

Your mobo will have one or more pinouts labeled SYS_FANx for case fans. Depending on your BIOS, it may actually control the speed of the fans connected to these pinouts, based on temperature sensors built into the mobo. On some systems the control configuration is done inside the BIOS Setup screens. On some it is not, and access is via a software utility provided with the mobo on a CD.

If you don't have enough mobo pinouts for your case fans you can always power them from the PSU directly, usually from some 4-pin Molex connectors (the large ones with 4 holes in line, intended to power IDE hard drives etc.). Fans with modern 3-pin female connectors on the end of their wires often will also have an adapter to let you connect to a Molex. In your case, the adapter is made with an additional female Molex connector on it, too, so that it "regenerates" a Molex output to replace the one you "used". When you use this power source the fan will always run at full speed. That is, unless you also buy a speed control module that connects between source and fan, and allows you to set it to one fixed slower speed of your choosing.

If it turns out that your mobo's pinouts really do provide control of fan speed only on the 4-pin connector (you can still plug into that any 3-pin fan), there is a way you could modify the wires to run TWO fans under control from that. You would splice together from the two fans the black wires and red wires (separately) on one connector, but do NOT splice the two yellows together. Just leave one yellow wire not connected. This will power both fans in parallel from one variable voltage for speed control, but the mobo will receive the speed measurement signal from only one of the two fans - the other will never be known. From what I read around here, most mobo pinouts can power two fans in parallel, but not more than that.
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April 12, 2010 8:00:38 PM

Awesome. So it sounds like I just need to hook up the three case fans to the SYS_FAN connections directly, hop into the BIOS when I fire up the machine, and see if I have control over all of them or not. I think I will only have control over the one (SYS_FAN2 on my mobo), but we'll see.

As for the splicing you mention, I understand everything up until the yellows. So I have one three pin fan connector plugged into the 4-pin SYS_FAN2. I splice the 2nd fans red onto the red and the black onto the black, but then just leave the yellows as is, correct? The temp sensing is accomplished through the yellow plugged into SYS_FAN2 and the voltage and ground are sent through the spliced wires over to the 2nd fan. The 2nd fan basically doesn't have its yellow wire hooked up to anything. That correct?
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a b ) Power supply
April 14, 2010 5:04:30 PM

Exactly right. Just tape up the end of the second unused yellow wire so it does not short out at some bad place, and maybe coil it up neatly. The speed of the fan with the unconnected yellow lead will never be known.
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April 14, 2010 5:35:46 PM

Best answer selected by Dre325.
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April 14, 2010 5:39:41 PM

Actually the speed will be exactly the same as the fan it is spliced to, which is known and controllable. I've hooked it up this way and all works fine. My Bios shows the fan2 speed, but I'll have to add some software to set the speed automatically. I haven't tested whether or not the fan is already changing speed (I haven't even installed windows yet!)
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April 14, 2010 6:04:29 PM

Dre325 said:
Actually the speed will be exactly the same as the fan it is spliced to, which is known and controllable. I've hooked it up this way and all works fine. My Bios shows the fan2 speed, but I'll have to add some software to set the speed automatically. I haven't tested whether or not the fan is already changing speed (I haven't even installed windows yet!)

Actually, the two fan speeds may or may not be the same. If the electrical impedances of the two fan motors are the same, then the current will split evenly. If the loading vs. speed curve of the two motors are the same and the fans provide the same resistance, then the rotational speeds would be the same. In other words, the two motors and fans have to be the same for your assumption to hold true.

Check out the SpeedFan app once you're set up, the current version is 4.40. It allows fan control and reports temps and more. Their website lists motherboards that support fan-speed control. Your board probably has a utility as well, but they usually are less than ideal.

If you can't control the speeds with software—and even if you can—you might consider adding a hardware fan controller. I've just posted a thread on this, you might want to follow it.
http://www.tomshardware.co.uk/forum/280060-10-controlle...
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