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Combination of fan control

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May 23, 2011 10:38:08 AM



Hi all,

I've almost done assembling a new system (my first) and I'm left with the control type of fans dilema.

my MB supports PWM and can work with EasyTune6.

The thing is, I really would like to have a physical control over the fans as backup (not via a software but by knobs) should the automatic control fail (in TC the temperature sensor will "ware out" and in PWM maybe a bug or a virus...)

I wish someone could help me out with the following questions (or just with one), I'm really stuck with this:

1. Is it possible to have this sort of combined control over fans?

2. reffering to the CPU fan specificlly- is this fan always on and always on full speed (no control)? Or is it controlled seperatably than the case fans because of its importance?
I sortta understood that PWM means that when the CPU "feels" load it signals the case fans to start working, but what controls the CPU fan itself?

3. Does PWM control signal to all fans to work at once (noisy and not economic) , or it can signal a single fan?

4. I think TC's advantage over PWM is that each fan is controlled indepandently (has its own sensor that triggers it on), which is less noisy, more economic, and should one fan fail, the others kick in as backup. What do you think?

a lot of thanks in advance :love: 
a c 142 ) Power supply
May 23, 2011 4:52:37 PM

1. Some cases (i.e. Antec DF-85 / 1200) provide manual fan control via 3 speed switch or adjustable speed knobs. You can also buy a fan controller but they bypass BIOS control. Asus kinda made it possible to do both w/ their OC Station but it didn't sell all that well given it's price tag.

http://www.asus.com/Motherboards/Accessories/OC_Station...

2. Normal 3 pin fans are controlled by voltage.....problem is at the lower voltages, many fans have trouble "spinning up" .... that is below 50% voltage, they don't get enough "kick" to start spinning. You have to give them a "push" to get going. That generally limits their range to 50 - 1-00%. PWM fans OTOH, control the fan speed by pulsing the full voltage, this over comes the "start up" problem and gives a wider speed range.

3. You'd have to use a PWM splitter to control multiple fans.
http://www.frozencpu.com/products/10350/cab-183/Akasa_P...

4. An enthusiast MoBo will have multiple fan headers. The Rampage 2 Extreme for example had 8 of them ..... 1 CPU, 1 PWR, 3 Chassis and 3 optional connectors that were linked to provided thermal sensors. All 8 fans could be controlled via the BIOS. PWM is normally only provided for the CPU fan.
May 23, 2011 5:52:48 PM


Thanks a lot for the answer, it really made it clearer.

I'll check my MoBo specs and check if a case with that feature of the Antec DF-85 / 1200 is on my budget.

What do you think about my argument though, about the need to have both manual and automatic control? According to your experience, do you feel it's necessary or are those auto systems reliable and long lasting (say a 5 years period)?

Related resources
a b ) Power supply
May 24, 2011 3:33:31 AM

Automatic control of fans built into the BIOS is very reliable. I do not see how having manual control as an option would help much. How would you know when to intervene and change it? Can you spend as much time as your BIOS chip can just checking all the temperatures to know that a fan is misbehaving? You might want to check into the details of the temperature controls in the BIOS of your mobo, although that could be difficult - many mobo manuals give very incomplete descriptions of those control systems. But most systems I have seen allow you to select an option (often separate choice for each fan output connector) in which you manually set the fan speed or voltage as you wish, rather than having the automatic control do its job. Of course, you're still using the BIOS system, and not a separate manual speed control.

Maybe an understanding of how they work would help. Many mobos have three types of fan power output connectors: ONE for the CPU, ONE for the PSU, and one or more for the case fans (or SYS_FANs). The one for the CPU is ONLY for use with the CPU cooler. The one for the PSU is ONLY for connection to the PSU via a wire set from it that looks just like a regular fan connection wire, and comes out of your PSU. NOTE that not all PSU's have these leads. The one(s) for the SYS_FANs are for case fans.

The PSU Fan connection is odd. In fact it is not intended to provide power to the fan in the PSU, nor to control it. All it is really intended for is to take the PSU fan's speed signal and check it and display it for you. On some mobos, apparently this mobo connector actually does have a voltage supply that you can run a normal fan off of, but it may not do any speed control of that fan. But in general, do not use it for anything other than monitoring the PSU fan speed. Now, that PSU fan MAY actually change its speed, based on a control system built into the PSU itself, and completely independent of the mobo. In fact, some will not start up until the PSU warms up, causing people to worry when the PSU fan does nothing when first turned on!

The CPU_FAN connector is ONLY for the CPU cooling fan. Every CPU has its own temperature sensor built into it and that temp is monitored by the mobo. Using that, it will alter the CPU cooler fan's speed to keep the CPU temp under control. The only exception is people who want to do their own manual CPU fan control, or to just run that fan full speed at all times.

The SYS_FAN connectors base their control of fans connected to them on a different temperature sensor built into the mobo. There might be separate sensors for separate SYS_FAN outputs, or they may all work from one common sensor.

3-pin fans have three wires from fan to mobo connector. Black is Ground, Red is the +12 VDC (varying) supply, and Yellow is the fan speed signal. That speed signal is a series of pulses (two per revolution) generated in the fan motor and sent back to the mobo for monitoring and display. Note that the control is NOT based on fan speed - that speed is just for your info. Oh, and one other safety check: some mobos will send out an alarm if a fan speed drops to zero when it should not. This is especially important for the CPU fan, which should NEVER drop to zero. Control of speed of a 3-pin fan is by changing (reducing) the +VDC supply voltage, based on the difference between the actual measured temperature at the sensor, versus the setpoint of desired temperature. The closer the truth is to the target, the slower the fan can run, as long as the temp does not rise. When it does, the voltage is increased to speed up the fan until temp is kept normal.

A 4-pin fan works a bit differently. It has those same three signals, except that the +12 VDC line is always that voltage - never reduced. The fourth line is the PWM (pulse width modulation) control signal supplied to the fan. Inside the fan motor case is a tiny controller that uses the PWM signal to switch the actual current through the fan motor (from the 12 VDC supply line) on and off in fast pulses. The longer each pulse is on, the faster the fan goes.

PWM or varying voltage are simply two different ways to achieve control of fan speed. PWM does have some advantages at low speeds. But in each case, the fan speed is decided by what is called a feedback control loop. For each fan output there is a setpoint or target temperature, and there is a sensor someplace (in the CPU or on the mobo) that measures actual temperature. The deviation between these (Measured - Setpoint) is multiplied by a gain factor and shifted by a zero offset factor to generate a controller output signal. This will be either a DC voltage between 0 and +12 for a 3-pin fan, or a pulse train of a variable width for a 4-pin PWM fan. As the measured temperature changes, the controller senses a change in the deviation and processes it into an updated output signal. This is a constant operation, responding in tiny fractions of a second to very small changes in the temperatures under control. It can do a MUCH better job than any person can, as long as it works. And these systems really are very reliable.
May 24, 2011 4:33:57 PM



Thanks a lot for your answer Paperdoc, I'm very new to hardware, so it took me a while, and having read the answers a number of times, I hope I got it:

case fans are always controlled according to the desired temperture minus the recorded temperture that the system temp detector on the mobo "feels", wether the fans are PWM or regular 3 pins, unless I chose a target voltage or target speed for them.

If I choose a target voltage or target speed for the case fans, they're always going to run at a constant speed, never shutting down (I understand this also a feedback loop Vdesired-Vrecorded, but approximatly at constant speed and almost always on).

So if I want a quiet and energy saving system I should'nt do the latter.
And if I really want a quiet and energy saving system I should use a PWM fans because the pulsed input enables them to run on lower voltages.

The PCU fan has its own temp detector and I should get a PWM for it, because everyone says PCU fans are espcially noisy and because this fan is always on (at varying speeds) and therefore consumes a lot of energy.

Now, I guess a TC case fan "asks" the mobo for voltage according to its own temp detector read, which will also require disabling the mobo case fan control.

A manual control, would mean (I guess) , also disabling the mobo case fan system- temp-assoiciated control, having an external device (the panel) "asking" the mobo for the desired voltage, and the mobo delivering it to the case fans.

I also think that auto control of case fans is better, I thought of manual as backup, this is why I asked if it's possible to have both. So to conclude, the only kind of combined control possible to obtain is using a mobo controlled fans, and in the time of need manually change settings via software.

Regarding the separate control of case fan issue, with mobo control they would all kick in at the same time and speed, unless you use a thing called a splitter or unless they are connected to different headers.

three more question (if I may, anyone :sarcastic:  ):

1.If the mobo specs state there's only one case fan header, how many case headers can I fit in theory, would that be as much as the case allows? (ignoring the fact that many fans are not always needed)

2.Considering the GigaByte mobo H67MA-UD2H-B3, the overview section says it has a CPU PWM controller (not a a CPU fan PWM controller), is that the same?
http://www.gigabyte.com/products/product-page.aspx?pid=...

3. Can you understand from the specs if this particular mobo supports a PWM control of CASE fans? and how could you tell?

P.S. Don't worry, I'm not going to build it myself, I just get to decide on the parts :p 

a b ) Power supply
June 13, 2011 3:29:56 AM

First, go to that gigabyte website you posted above, and there is a picture of the mobo near the top, with two tiny pictures below it. Click on the blue mobo picture, and a window will open up with a large view. Even better, once it is downloaded you can hover the pointer over the main pic and it will show you a blown-up version on the right. Use these to follow what I say next.

1. Yes, it appears this mobo has only one header for case fans, labeled SYS_FAN. On the board, look at the lower left corner. Above three black blobs, and below three light blue SATA connectors, is a WHITE connector that says SYS_FAN right above it. Look closely and you'll see that it has 4 pins, so it is for a PWM case fan. So you only get to plug into it one case fan unless you use a fan splitter or do some soldering and splicing yourself. From many notes around here, it appears you CAN power two fans off one header, but maybe not three. (The limit seems to be the heavy current used to start up a fan at the beginning.) Now, There is one thing often ignored when you splice together the leads from two fans to run them off one header. The four leads of the fan, with the Intel standard color coding, are:
Pin 1 is Ground, wire color Black;
Pin 2 is +12 VDC, wire color Yellow;
Pin 3 is Sense (the Fan Speed Signal), wire color Green; and
Pin 4 is Control (the PWM signal), wire color Blue.
HOWEVER, not every fan maker follows these color codes, BUT those signals are always on those pins of the connector. Look very closely at the white connector, on its right side next to the little metal can capacitors with blue spots on them.
You can see a white tongue of plastic sticking up from the connector base, the width of the lowest three pins, but not extending up to the fourth pin. This tongue (used to ensure the plug from the fan is fitted on correctly) is besides pins 1 to 3, and pin 4 is by itself. So that's how you can tell which pin is which on the connector. NOW we get to my point. If you connect two fans with all four of their wires in parallel, you will supply Ground, voltage, and PWM control signals to both, and that is fine. BUT the fan speed signals on pin 3 are generated by the fan motors themselves and fed back to the mobo on this line. The signal is a series of pulses (2 per revolution). If you connect BOTH fan speed signals together, the mobo will receive a mess of two pulse trains mixed together and it cannot figure out the fan speeds. SO, connect ONLY ONE of the Pin 3 wires from a fan to the mobo. Leave the fan speed wire from the second fan just not connected to anything, and this fan's speed will NOT be monitored. However, it is VERY likely to be the same as the one that IS monitored, because it will get all the other signals the same.

2. OK, now the CPU cooling fan. I did not find the specific phrase you cited. But look again at the mobo picture, and zoom on the center of the board. You'll see part of the big CPU socket on the right on the zoom frame. Just left of its bottom left corner, about lined up with the bent wire CPU lock lever, is another 4-pin fan connector labeled CPU_FAN. Again, it uses a PWM fan, so that's what you should try to get for this function.
!