Apr 30, 2021
7
0
10
0
Anybody know what this means and how it works?
My existing rear mounted chassis fan has a three pin plug mounted on the MB 4 pin connector which from reading a number of posts hear means that it is constantly running at max speed, although fan monitoring software is saying that it changed speed with temperature. As the fan is becoming noisy, I thought I would upgrade to a new one and add a front mounted fan to improve air flow. However, I am unable to find information on what ASUS call DC Mode on pin 4, and searches for 4 pin DC control fans doesn't reveal a lot if anything. So what is it, what fans do I need and how do I run both fans from the MB giving temperature control?
 

Lutfij

Titan
Moderator
Welcome to the forums, newcomer!

PWM is Pulse Width Modulation and DC is Direct Current. The latter means that voltage is actively managed on the header to manipulate the speed of the fan. The former relies on a signal to regulate when power is given to the fans. As for your fans, look for 4pin PWM fans and look for a PWM fan splitter/hub like the ones CoolerMaster, Phanteks and Deepcool make. you can have all the fans on the splitter/hub then have the hub connected to the CPU_FAN. That way all fans are regulated by one header and when the CPU temps rise, the airflow in your case is ramped up/managed.
 
Apr 30, 2021
7
0
10
0
Thank you Lutfij for your response.
Having read a number of posts here on Tom's hardware I was aware of the detail with PWM fans, hence the request for more information on the ASUS 4 pin DC Mode as I haven't found anything on it yet.
This mother board only has one PWM fan control and that is for the CPU. Yes the solution you suggest is an option but some posts don't recommend using the CPU PWM as an option saying it should be kept separate from anything else. Of course using the CPU header with a splitter etc means that the case fans will be hidden from the MB and the MB temperatures controlled by the CPU temperature monitor. As it is the MB temperature progressively rises during use with the CPU temperature way below it. Also any mal function of the CHA fans will not be recognise with this option. Looking at the splitters/hubs you suggested, the Phanteks option appears to be most suitable, should I choose to go down that route.
My reasoning was that ASUS must have offered DC mode for 4 pin CHA FANS because solutions/hardware was available. All I wanted to know is what to look for in fan specification to use it.
 

Paperdoc

Champion
Ambassador
That is an early board, and its manual does NOT make it clear what the only CHA_FAN header can do. In more recent mobos each 4-pin fan header can be set to use either the older Voltage Control Mode (aka DC Mode) required by 3-pin fans OR the new PWM Mode ideal for 4-pin fans. Your mobo's manual gives NO info to suggest that you can make this choice on that header, and the labels on it also do not tell us. Now, one of the backwards compatibility features of the newer 4-pin PWM fan design is that it CAN function properly when connected to a header that only uses that older DC Mode, even though that means it is not actually using the PWM feature. So SOME earlier mobos (maybe yours) are fitted with 4-pin headers that only do the older 3-pin DC Mode, and that works for BOTH fan types.

HOWEVER, the common design of fan HUBS actually REQUIRES that it be connected to a header that IS using the new PWM Mode so that the Hub can receive the PWM signal from Pin #4 and relay that on to all its fans. That also means that the FANS used with that Hub MUST be the new PWM design. So, you can NOT use a normal Hub if that CHA_FAN header on your mobo is only able to operate in the old DC Mode. (We cannot tell from the mobo manual whether that header is limited this way or not.)

There IS a solution to this dilemma, and that is the Phanteks Universal Fan Controller, Model PH-PWHUB_02. It is unusual in two ways. First, it CAN work with either type of mobo header Mode - it adjusts itself to the type of input signals it gets from the header, and then converts that to what its output ports require. To do this, you do NOT use the manual speed control button box supplied; instead you use the cable supplied to connect from your CHA_FAN header to the Hub's INPUT socket and thus feed it the mobo signal. Secondly, it has three ports for plugging in older 3-pin fans, four ports for new 4-pin fans, and a Port #1 that can handle either fan type. For each port the Hub generates the correct signal type for its fan type - Port #1 apparently can detect and adjust for whatever is connected there. (Port #1 is the ONLY output port able to send back to the mobo host header the speed of its fan - fans on the other ports cannot report their speeds.) So, even though you do not know what type of control signals your CHA_FAN header sends out, this Phanteks Universal Controller CAN be used to connect several fans to that single header, AND can handle fans of either type - whatever you have.

By the way, do not attempt to use the PWR_FAN header at the top next to the CPU_FAN header. That was used with an older design of PSU that had a special set of 3 wires coming out of it and ending in a 3-pin fan female connector. Its only use was to send to the mobo for display and monitoring the speed of the fan inside the PSU. Almost no PSU's now have that feature, so that mobo header is not used for anything.
 
Apr 30, 2021
7
0
10
0
Paperdoc. Thank you for the information. It sounds like I really need to get to the bottom of what the MB is doing on the Pin 4. I know some ASUS MB's actually show 5 v for this pin. If the voltage is constant, no matter how good the Fan Controller is I am not going to have fans controlled by temperature. Do you think it is worth measuring the voltage on pin 4 with a digital meter to see what happens?
Reading your post above with the Phanteks controller, is the manufacturer saying that with the controller it can vary the speed on 3 pin (non PWM ) fans? Is this by varying the voltage on pin2?
PWR_Fan noted.
 

Paperdoc

Champion
Ambassador
A 3-pin fan's speed can be controlled ONLY by varying the voltage supplied on Pin #2 (#1 is Ground), from 12 VDC for full speed to about 5 VDC min to avoid possible fan stalling. A 4-pin fan under PWM Mode of control will always receive on Pin #2 the full 12 VDC. In addition it receives from Pin #4 the PWM signal. That fan design includes a small chip internally that uses the PWM signal to modify the flow of current from the fixed 12 VDC supply though the motor windings, thus altering the speed. If it is connected, instead, to a header using the older DC Mode, the fan recevies no PWM signal so it cannot modify, BUT the supply voltage is now varying per the 3-pin fan control system, so the motor still does have its speed controlled. On the other hand, of you plug a 3-pin fan into a 4-pin header that is using the new PWM Mode, that fan receives no PWM signal from Pin #4 (which it could not use anyway, lacking the special chip) but does receive a fixed 12 VDC power supply, so it runs full speed all the time.

The PWM signal on Pin #4 is a lot like a classic "square wave" that is fully either on or off. In a square wave the "ON" portion of the wave is exactly 50% of the time always. In a PWM signal the "On" portion is varied from 0% to 100%, so we refer to its setting as its "% On". For computer case fans, that signal is operating approximately at 20 to 22 KHz, and the voltage of the signal (referenced to Ground) is +5 VDC for On, and 0 VDC for Off. THAT is why some mobos label Pin #4 as "5 V" - it is NOT a fixed 5 VDC line, it carries a signal that is 5 VDC peak voltage in a PWM wave. So you could NOT tell using a voltage meter what is is doing. An oscilloscope, yes, but few have one handy.

The Phanteks Universal Fan Controller does do the conversion from one input signal type into two different types of outputs. Outputs to its 4-pin ports are in the PWM Mode, and outputs to the 3-pin ports are to the older Voltage Control Mode. For Port #1, it indicates, the unit determines which type of fan is connected and outputs there whichever type of signal is appropriate. (Many modern mobo headers can do this automatic detection - it's now common.) Phanteks and a few others previously had a Hub model fully capable of doing most of this. What is new in this particular Hub is that is now ALSO can detect which type of INPUT signals it is receiving from the mobo host header, and adjust its conversion actions to deal with either type. Previous models were able only to convert from PWM inputs to Voltage-controlled outputs, but not the other way.

OP, for your situation since we do not know what your mobo CHA_FAN header is doing, I suggest the Phanteks unit because it CAN deal with whichever is feeding it and you do not need to know the details. But if you do want to know, here is how to tell. You need a 3-pin fan. Plug that into the CHA_FAN header. Boot up and go immediately into BIOS Setup. See your manual, p 2-24 and 2-25. First, set the CHA_FAN Profile to TURBO, then use Esc to return to the Monitor Menu (p. 2-23). There NOTE what it says about the CHA_FAN speed. Hit F10 to get to the Exit Menu (p. 2-31) and choose the Save Changes and Reset. This will reboot your system with the new setting, but you should again go immediately into BIOS Setup. Get back to the Monitor Menu and look at the CHA_FAN speed again - it may be higher now. Note that. Now, go forward to the CHA_FAN header and change its Profile to SILENT. Back out to Monitor Menu, note the speed again, then go through Exit etc. Finally, re-enter BIOS Setup and note what the fan speed is under this reduced-speed setting. It SHOULD be much slower IF the header is using the older DC Mode that CAN control the speed of a 3-pin fan. But IF the header is using the new PWM Mode, than the fan's speed will ALWAYS be full speed no matter what setting you make. That's a sure-fire way to detect what Mode the header is using.

FYI, all those steps into and out of BIOS Setup are there because, when you make a change to a setting, on many mobos it is NOT used until you SAVE and re-boot. On some it MAY be implemented immediately, but we don't know about your mobo.
 
Apr 30, 2021
7
0
10
0
Thank you for that. I will try that shortly.
I suddenly realised that I had recently changed out the CPU cooler for something better but the old fan was still running but noisy and it was a 4 pin with PWM. As a trial, I have connected this 4 pin PWM to the CHA_FAN socket to see what happens. So far nothing has gone bang nor is there any smoke but what is interesting is that the fan speed is varying from 1923 to 3154 with temperature according to the ASUS fan monitor but for every change of the CPU temp the speed changes on the CHA fan at the same time. There does seem to be some co-ordination going on between the MB temp and the CPU temp reflecting the slow increase of the MB temp but the CPU temp appears to be the over riding factor. As it sit here typing, with the side panels off the chassis, (to keep it cool) I can hear the "CHA fan changing speed. HWInfo also showed this when I was using it but I put this down to that monitor having difficulty recording the detail.
I will let you know what the test detailed above reveals. Thank you again.
 
Apr 30, 2021
7
0
10
0
I have now gone through the test you described above. With a MB temp of 28 and set to TURBO I was seeing fan speeds of 1275 to 1295 rpm. Set to SILENT and with the same MB temp I saw speeds of between 904 to 905 rpm. I have to report that for both CPU and CHA I normally have the options set to manual and in manual mode the CHA fan at 27 was running between 1544 and 1670RPM .
So, if I read your post correctly, the DC Mode on this MB is controlling 3 pin fans. However, in saying that, from my previous post, using the 4 pin fan also shows changes in fan speed with temperature. What I do from now - I am confused. Could it be in 3 pin mode it uses the MB temperature but in 4 pin mode the CPU temperature is also used?
As an aside running the PC with the side panels off is showing a much cooler MB temperature - down at least 4 degrees, so I think I will need to do something about the cooling whatever I do.
 

Paperdoc

Champion
Ambassador
The experiment tells us the CHA_FAN header is using the older DC Mode, at least when it is controlling a 3-pin fan. See the middle of the first paragraph of my last post about what happens with a 4-pin fan on a DC Mode header. That fan's speed IS controlled this way because of the backwards compatibility design of the 4-pin fan.

Now, it is POSSIBLE that the CHA_FAN header you have does what the latest designs do - test the fan that is connected at every start-up and determine whether or not it can respond to a PWM signal. If so, set to PWM Mode; if not, set to DC Mode. This is called true "Automatic" Mode selection. BUT it's a fancier feature, and almost all headers that do have this Auto Mode selection brag about it AND offer you the option to make your own choice in BIOS Setup. In early mobos (yours is of that age) it was MUCH more common to use a 4-pin header BUT apply only the older DC Mode which CAN control the speed of either fan, as you have experienced. So the test I suggested does not prove that your CHA_FAN header can NOT use PWM Mode. But it is likely that way. It does prove that it CAN use DC Mode.

That early "universal" design that uses only DC Mode with a 4-pin header is just fine when you are using one fan. It is a problem only when you try to use a fan HUB on the header, because a HUB must have the PWM signal from that header to relay to all its fans. AND the fans MUST be PWM new style so they have the special chip to USE that signal.

So now we CAN get to your main question. The rear fan you propose to replace is a 3-pin model. The CHA_FAN header CAN control a 3-pin fan by using DC Mode, and it is VERY likely that it does NOT know how to do the new PWM Mode. Thus you should NOT plan to get a fan HUB. Instead, you should plan to use a fan SPLITTER, which is the only good way to connect several THREE_pin fans to a mob header that uses only DC Mode. PLUS, you should buy only 3-pin fans, since they are what your header can control AND they are a little cheaper than 4-pin models.

How to tell the difference? A SPLITTER has only two types or "arms". It has ONE cable ending in a female fan connector with 3 or 4 holes. It has two or more outputs "arms" with male (with pins) connectors to plug your fans into. Those are the only types of "arms". However, it may appear to be a collection or cable "arms", or a small circuit board with headers, or a box with sockets recessed into the case. And FYI, 3-pin SPLITTERS are getting hard to find because a 4-pin model will work just fine, too, with 3-pin fans and headers. Note that the ONLY power source that feeds a Splitter is the host mobo header, so that header's limit of 1.0 A max current load to ALL of the Splitter's fans applies.

A HUB can look very similar, AND many sellers MIS-label both of these device types, so be careful! A HUB has s THIRD "arm" that must plug into a power output connector from the PSU (either SATA or 4-pin Molex) to get more power for its several fans than a Splitter can get from a mobo header. That is how a Hub evades the 1.0 A current limit of the host mobo header. But as I said earlier, almost all HUBS must have a PWM signal from a host header operating in PWM Mode, and can control the speeds ONLY of 4-pin fans.

So in your case, OP, the HUB will not do the job. Get a SPLITTER. You can check the max current specs of the fans you plan to connect. I fully expect NO problem there. Most modern fans draw from 0.10 to 0.35 A max each, so three or even four of those on one header using a Splitter is quite acceptable.
 
Last edited:
Apr 30, 2021
7
0
10
0
Paperdoc thank you for all your help, advice and patience in explaining all this to me. As you say, the only aspect that has been proved is that this header is running in the old DC Mode, so I think, as you say, purchasing 3 pin case fans with a splitter is the way to go.
One final point if I may. I am assuming the CHA_FAN header uses the MB temp sensor to control the CHA Fans. Is this correct, or is this something else that is not clear due to the lack of guidance from ASUS?
 

Paperdoc

Champion
Ambassador
I'm sure your assumption is correct. Virtaully all mobos have two very similar fan control systems. The CPU_FAN header ALWAYS uses only the temp sensor built into the CPU chip itself. Then the CHA_FAN normally uses a different sensor on the mobo for case fan control. In more recent mobo designs they often allow you additional choices of selecting alternate temp sensors for a CHA_FAN header. But with no options available there, it is surely that mobo sensor that is used, and that's the correct one for such fans.
 
Apr 30, 2021
7
0
10
0
For completeness sake, I found this information on the Overclockers website for the Phanteks Universal Fan Hub. Basically, as it is mentioned in the posts above, I thought I would copy the information here. The website is :-https://www.overclockers.co.uk/phanteks-universal-pwm-fan-hub-black-ca-08x-pt.html
The paragraph in question is detailed below. As I only have a voltage regulated 3/4 pin connector for the CHA Fan it was of interest to me. Not any more! I have copied it here because I was not aware of it and hadn't seen this statement elsewhere.
"Note: If the 4-Pin PWM cable of the hub is not connected to a PWM connector on the motherboard, but instead to a 4-Pin- or 3-Pin port that is voltage regulated, the additional SATA power connector cannot be used, or all fans will spin at full speed. By omitting the SATA power connection to the power supply, the maximum load capacity of the PWM hub is limited to a total of 30 Watts."
 
Thread starter Similar threads Forum Replies Date
A Cooling 6

ASK THE COMMUNITY