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Case Fans to PSU or to motherboard?

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February 12, 2013 10:13:21 PM

Hey guys,

I recently bought the Cooler Master CM 690 II Advanced case (CM 690 II Advanced (USB 3.0 version) - Cooler Master).

Receiving my Asus P8Z77-V LE mobo tomorrow (ASUS P8Z77-V LE Intel Motherboard - Newegg.com)

I've been reading a lot of varying opinions on the matter; some say it's best not to draw more power than needed from the mobo, and to attach the fans to the PSU directly, while others disagree.

I understand that connecting to mobo allows fan speed control while connecting directly to PSU has fans running at full speed all the time.

I'm not sure if I want to be able to control the speed, but I would assume that's a good thing to have, no? (Is there any advantage/disadvantage, other than acoustic, to being able to control the fan speed?)

What do you guys think?

My other question is this: mobo has 2 4-pin chassis fan headers and 1 3-pin power fan header.

What exactly is the power fan? From what I understood, I can connect a chassis fan to it, but wouldn't offer any speed control...is that right?


Thanks!

More about : case fans psu motherboard

a b ) Power supply
a b V Motherboard
February 12, 2013 10:47:50 PM

Power fan is for your PSU. On some units the fan will be speed variable, this is where you plug it into your motherboard to control the speed.
Go ahead and plug your fans into your motherboard, advice like that is what you see in youtube comments. The worse place for computer advice ever. I know that fans take under 5w of power, probably closer to 1w, seeing as the CPU will draw about 95w itself, you can see fans power draws is not significant.
a b ) Power supply
a b V Motherboard
February 12, 2013 10:48:35 PM

Oh yeah, and you can indeed stick a chassis fan into the system fan header, it'll just run at 100% so it doesn't matter.
Related resources
a b V Motherboard
February 13, 2013 12:23:10 AM

Sometimes it is better to use the motherboard fan connectors so you don't have to open the case to actually see if the fans are spinning, you can use the bios PC Health to check their Status or even a software app that has the capabilities.

However, on the other hand, as more power is required to go through the motherboard to power the fans, it might impact on the motherboard load itself but I think that is miniscule and besides, you'd have to use connector adaptors to fit to a PSU.

Also when fitting cables to the PSU, it is recommended to use one line of cables for similar voltages like the fans would go on one line of cabling and the hdd and CD/DVD drive on the same line of cabling, or separately.

You should use at least one chassis fan, that is one that is fitted to the actual case either at the rear above the ports or on the side lid, if screw holes and vent allow for it. (sometimes at the front of the inner case area, near the power button). The chassis fan should be about 12 v 0.6a...

The fan for the CPU is usually called CPU FAN and is located with 2 inches of the CPU. Using the appropriate fan connectors will ensure the proper readings for each connected fan, using a chassis fan connected to the CPU Fan connection will give the wrong readings.
a b ) Power supply
a b V Motherboard
February 13, 2013 2:48:49 AM

As a general rule, I recommend using the mobo ports for fan power, for several reasons:
(a) You get automatic control of the fan speed regulated according to actual measured temperatures in key components, so fans run what is needed, no more (less noise), and no less (more cooling when temps rise);
(b) You get mobo monitoring of fan speeds if you wish to "see" them yourself with either BIOS display or, with your mobo, an app (ASUS AI suite II, Manual p. 1-6) included on the mobo CD; and,
(c) Most mobos today (can't say for sure about yours) monitor the CPU cooler fan specifically and will give you a BIG warning or completely shut down your machine if the CPU fan fails, as a damage prevention measure.

For your specific case, I will add more comments.
1. Your mobo does not appear to have a PSU_FAN or PWR_FAN port. And I disagree a little with mace200200 - AFAIK, these ports do NO control of a PSU's fan speed, they only can MONITOR that speed if your PSU has the appropriate leads coming out of it to plug into this mobo port. The PSU does its own fan speed control internally. Since it does not ever try to control a fan speed, this mobo port can only run a case fan (if it is plugged in here instead of the special PSU leads) at full speed. But as I said, you don't have one of these, anyway.
2. I especially recommend that you connect your CPU cooler system to the mobo's CPU_FAN port. NOTE that this fan should be a 4-pin fan design. If you try to use a 3-pin fan for this job, it may not be speed-controlled, and run only at full speed always.
3. ALL four fan ports on your mobo are 4-pin. Among mobos there are several ways that 4-pin and 3-pin fans can be connected and controlled, but your mobo's manual does NOT indicate it can adapt to 3-pin fans. SO, to use your mobo's three CHA_FAN ports, you will need 4-pin fans to be sure they can be controlled properly. Now, that MAY be a problem with the three fans that come with your case. The case website does not make anything clear about the fans that are included, other than their size and speed.

Here's why Item 3 is important. Many fans supplied with a case are equipped with what are known as 4-pin Molex power supply connectors, and these are NOT the same as a "4-pin fan connector". The "4-pin Molex" (or, more correctly, the Molex 8981 connector) is about 1" wide with 4 connection wires, and was originally used for power directly from the PSU to IDE devices like HDD's and optical drives. Its 4 wires provide separate supplies of 12 VDC and 5 VDC. When used for fans, only 2 of its wires are in use - the Ground and +12VDC lines. That means the fans can only run at full speed. A "4-pin fan" connector is much smaller - about ½" wide and not as thick - and it clearly fits on a mobo fan port. A 4-pin fan also uses 4 wires, but they are VERY different from the Molex 8981 power supply system. On a 4-pin fan, the first two lines are Ground and +12VDC, again. Pin 3 is the fan speed signal. It is generated inside the fan motor as two pulses per revolution, and is sent back to the mobo port where it can be monitored for speed readout. Pin 4 in the PWM signal. There is a small chip inside the fan motor that uses this signal to control how much of the +12VDC supply actually does flow through the motor, thus controlling its speed. Older fans used 3 pins, and operate a bit differently. Pin 1 is still Ground. Pin 2 is the +VDC supply, and Pin 3 is the speed pulse signal. But in that system, the mobo achieves speed control by varying the +VDC supply from 0 to 12 VDC. (Remember that the 4-pin fan system keeps this voltage constant at 12 VDC.) But basically, a fan designed to be powered from a PSU's Molex 8981 output connector is a "2-pin fan" because it only has connections for the Ground and +12VDC lines.

Now, it IS possible to get an adapter to allow you to connect a fan designed for the Molex 8981 supply connector to a mobo fan port, BUT there are two real limits there. The obvious one is that a fan designed to be powered from a Molex 8981 connector does NOT have any speed signal to send back, and no wire for it, either. So even with an adapter to allow connection of the Ground and +12VDC lines to a mobo port, there is no fan speed readout possible. The other is that the only way to change the speed of such a fan is to reduce its supply voltage on Pin 2, just like a 3-pin fan system would. However, many 4-pin mobo fan ports do not do this - they operate ONLY in the 4-pin fan mode and keep that line at +12VDC always. So that way they cannot control the speed of that fan type.

Net result in your case is: I can't tell you right now exactly what your case fans can do, because the Cooler Master site does not say. IF they are fans with only 2 wires coming out of them and ending in the larger Molex 8981 connector, there is no real advantage to using the mobo ports for connection. You might just as well connect them directly to the PSU as they were designed. Otherwise you will have to buy real 4-pin fans that CAN use your mobo's ports properly. OTHERWISE, if the case fans actually are 4-pin fans with 4 wires from the motor ending in the smaller "4-pin fan" connector, you're all set!

Oh, one more wrinkle to note! ONE of the case fans also has blue LED lights, presumably intended for the front. I don't know exactly how those are powered. They MAY have their own power wires so that this one fan has more than 2 wires from it to its connector. OR they may be run off the main +12VDC supply, meaning that their brightness would be reduced by any system that reduces the fan's supply voltage for speed control.

The CPU Cooler fan does NOT come with your case, so you're either using one that comes with your CPU or buying one separately. I strongly recommend that you ensure it is a 4-pin fan and that you connect it to the mobo's CPU_FAN port.
February 13, 2013 2:31:32 PM

Thanks a lot for the replies guys!

mace200200 said:
Oh yeah, and you can indeed stick a chassis fan into the system fan header, it'll just run at 100% so it doesn't matter.


By "system fan header", do you mean the Power Fan header?

Paperdoc said:

1. Your mobo does not appear to have a PSU_FAN or PWR_FAN port.
3. ALL four fan ports on your mobo are 4-pin.


The spec sheet says:

1 x CPU Fan connector(s) (4 -pin)
2 x Chassis Fan connector(s) (4 -pin)
1 x Power Fan connector(s) (3 -pin)

Doesn't that mean there is a PWR_FAN port? Should receive the mobo soon, so I'll check, but from the specs listed on the Asus website (http://www.asus.com/Motherboard/P8Z77V_LE/#specificatio...), it looks like 3 of the 4 ports are 4-pin while the last one is 3-pin.

Paperdoc said:

2. I especially recommend that you connect your CPU cooler system to the mobo's CPU_FAN port. NOTE that this fan should be a 4-pin fan design. If you try to use a 3-pin fan for this job, it may not be speed-controlled, and run only at full speed always.


For now, I'll be using the stock fan that comes with the 3570K. Not sure if it's 3 or 4 pin, I should receive it shortly and will check!

Paperdoc said:

Many fans supplied with a case are equipped with what are known as 4-pin Molex power supply connectors,


All 3 fans actually came with molex connectors attached to them, so I have the option to connect to PSU directly or to the motherboard.

Paperdoc said:

IF they are fans with only 2 wires coming out of them and ending in the larger Molex 8981 connector, there is no real advantage to using the mobo ports for connection. You might just as well connect them directly to the PSU as they were designed. Otherwise you will have to buy real 4-pin fans that CAN use your mobo's ports properly. OTHERWISE, if the case fans actually are 4-pin fans with 4 wires from the motor ending in the smaller "4-pin fan" connector, you're all set!


The fans have 3 wires coming out of them (yellow, red, and black) to the 3-pin connector. And that 3-pin connector is connected to the molex connector, but only through 2 wires (red and black). I assume the yellow wire is for speed control? If so, I should be good connecting them to the 4-pin ports on the motherboard, and would get speed control, right?

Paperdoc said:

Oh, one more wrinkle to note! ONE of the case fans also has blue LED lights, presumably intended for the front. I don't know exactly how those are powered. They MAY have their own power wires so that this one fan has more than 2 wires from it to its connector. OR they may be run off the main +12VDC supply, meaning that their brightness would be reduced by any system that reduces the fan's supply voltage for speed control.


Yes, that's true! The front fan has blue LEDs. Just checked the cables, same as the rest of the fans; 3 cables going to a 3-pin connector, which is connected to a molex connector through 2 cables. There's another 2-wire cable (red and black) going to the top of the case, but I assume this is going to the LED switch on the top of the case (to turn on/off the LED lights).
a b ) Power supply
a b V Motherboard
February 13, 2013 9:20:38 PM

Yea, power fan and system fan are the same thing.

Yes you can plug a three pin fan into a four pin header, or the other way around. There's a notch on the motherboard and fan pin header so that you plug it in the right way. Your stock intel fan will be four pin, I would recommend getting an aftermarket heatsink sooner than later though. $30 will buy you as good of a cooler as you'll need.

And your right about the case LEDs too, it's just two wires.
a b ) Power supply
a b V Motherboard
February 14, 2013 6:28:50 PM

Apparently I was looking at the wrong manual for your mobo. So let me revise some items.

1. Yes, you certainly do have a PWR_FAN connector on your mobo - item 6 on manual p. 2-23. Note that is is a 3-pin port, BUT it is not really a "3-pin fan port" in the full sense. It does allow connection of a 3-pin fan so that the fan's speed can be fed to the mobo and read. Note that, in any display, whatever fan this is will be called the PSU Fan. However, this port cannot exercise any control over fan speed - it can only run that fan at full speed.

2. As you describe them, your case fans will come adaptable to either a standard "3-Pin Fan" mode, or to connection directly to a Molex 8981 power source. Do NOT connect to BOTH of those! Doing so would feed power from the PSU directly into the mobo's fan port and damage it. Chose one for each case fan:
(a) Connect to PSU's Molex 8981, and you get power from there not involving the mobo. You cannot read the fan's speed, and you cannot control its speed - it will run full speed always; or,
(b) connect to CHA_FANn port of the mobo. You will be able to measure fan speed, and MAY be able (next paragraph) to control it (them).
Whichever you choose on each fan, just tied the unused connector up to keep it neat and unused.

Now to part of the details of backwards compatibility of mobo fan ports. Mechanically, the connectors for both 3-pin and 4-pin fans can connect together. (Mobos have males, fans have females.) The mobo male connector has a tongue sticking up beside the first 3 pins, and the fan female connector has a slot on one side that fits this, so you can only connect them one way. Electrically, the first three pins are almost identical - Pin 1 is Ground (Black on 3-pin), Pin 2 is +VDC (Red on 3-pin), and Pin 3 is Speed Pulse (Yellow on 3-pin). The difference is that, in a 3-pin system, the voltage on Pin 2 varies from 0 to 12 VDC; in a 4-pin system Pin 2 is always +12 VDC, and speed control is done inside the fan motor based on the PWM signal on Pin 4.

So you CAN plug a 3-pin fan into a 4-pin fan port and it will work. Exactly how depends on what the mobo makers did for that port. There are three possibilities.
(a) If the port acts only as a standard 4-pin port, the 3-pin fan will always receive +12 VDC on Pin 2 and always run full speed.
(b) Some mobo makers offer an option set manually in BIOS to have this port change and behave like a standard 3-pin port. In this mode, the voltage on Pin 2 is varied to achieve fan speed control.
(c) Some mobo makers have automated this mode change process so that the mobo port itself determines what type of fan is attached and sets itself to either 3-pin or 4-pin mode for control.
Your manual does not say anything about a 3-pin operating mode for the CPU or CHA fan ports. So, yours MAY operate only as standard 4-pin ports, but they MIGHT operate in the other ways - you can only find out by trying.

If you want to have your mobo measure the speeds of your case fans, you must plug them into the mobo ports so that the Speed Pulse signals from the fan motors can be sent back to the mobo on Pin 3 of each port. But interestingly, CONTROL of fan speed does NOT link to this signal. Control is based only on a temperature measurement sensor for each fan port. The speed signal in Pin 3 is for MEASUREMENT only, and not control. The exception, in a way, is that some mobos will monitor the CPU_FAN speed and take protective action if it fails.

Regarding the CPU cooling fan, I repeat that I would connect it to the mobo's CPU_FAN port. That way the speed will be available to the mobo, and it MAY control that speed.

I see that the fan with blue LEDs in it does have a separate connector for those LEDs, so you can power the fan whichever way you like and not worry about the LEDs.
February 14, 2013 6:51:43 PM

Thanks a lot for your detailed replies!

I got my mobo and CPU yesterday. I ended up connecting the top and rear fans to the chassis headers, while the front fan with the LEDs directly to the PSU. The wire wasn't long enough to reach the power header anyways.

Thanks again!
!