Multiple case fans on one motherboard header

[artey1498]

Hey all -

Before I ask my question, I would like to point out that I am well aware there are multiple threads regarding the very issue I'll be talking about, it's just that I'm conflicted on what to think due to each one having different information/recommendations. I also realize I've posted another thread involving case fans, but I since have decided to bite the bullet and get two of them. The reason I'm making a thread about this is because I would like some final clarification, that's all.

I would like to know if it's fine for the motherboard to run multiple case fans (one case fan is 92 mm, one is 80 mm) off of one "CHA_FAN" header? I did some research a few days ago and bought a few things on Newegg to see if they could help me. One's a 4 pin pwm fan splitter cable (https://www.newegg.com/Product/Product.aspx?Item=N82E16812119872) and the other is a 4 pin pwm extension cable (https://www.newegg.com/Product/Product.aspx?Item=N82E16812162060). Now, I read on some of the threads I was looking at that each header can only support either 1A or 2A each, depending on the mobo. I think mine can support 2A, but I'm not 100% sure. I also read that having a splitter cable with the 4th pin reserved for pwm attached on each header is bad, because it'll confuse the motherboard. Does that mean that I won't be able to use the 4 pin splitter I bought? Also, the fans I have are the Blade Master 92: http://www.coolermaster.com/cooling/case-fan/blade-master-92/ and Blade Master 80:
http://www.coolermaster.com/cooling/case-fan/blade-master-80/.

I would prefer to not get a fan controller, seeing as how the y splitter cables have already been purchased, however I just want to make sure that I won't damage my motherboard in any way.

For some additional information, here is the link to my motherboard (although the one I actually own is a slightly different model with only two headers): https://www.asus.com/Motherboards/F2A55M/, as well as a link to my computer: https://www.asus.com/us/Tower-PCs/M11BB/. I appreciate any and all responses.

 

[boosted1g]

Two PWM fans on a spliter is completley fine, even if different sizes.

 

[artey1498]

Two PWM fans on a spliter is completley fine, even if different sizes.

So the motherboard won't get confused then? With having two different pwm fans plugged in?

 

[boosted1g]

No because in the splitter it should be missing pin 3 for the tach signal on the second fan.

 

[artey1498]

No because in the splitter it should be missing pin 3 for the tach signal on the second fan.

In the link contained in my post, the cable I ordered has all 4 pins for each fan thing (https://www.newegg.com/Product/Product.aspx?Item=N82E16812119872&nm_mc=AFC-C8Junction&cm_mmc=AFC-C8Junction-VigLink2-_-na-_-na-_-na&cm_sp=&AID=10446076&PID=8167372&SID=j29jz1zjjs000a1700053).

 

[boosted1g]

If you zoom in on the second picture you can see that the top right one only has 3 wires going to it.
Trust me, one of the 2 only has wires to pins 1,2, and 4.

 

[artey1498]

If you zoom in on the second picture you can see that the top right one only has 3 wires going to it.
Trust me, one of the 2 only has wires to pins 1,2, and 4.

Actually, I have the exact splitter connected to the 80mm and 92mm fans inside my computer, and all 4 pins are indeed attached to both connectors. I did plug in a 3 pin fan instead of the 4 pin I had though, so its not a problem anymore. However, now that both fans are plugged into the splitter, I've noticed that in the bios, the CHA_FAN entry has the rpm jumping like crazy. I see it go from 900 to 1400 to 2300 and then back, to only repeat the cycle. Is this a voltage problem or something? Also, I did some more research and found that the mobo will attempt to run both fans at the same speed, but since they're not identical won't that cause problems?

 

[Paperdoc]

I can understand how you got confused. There is a lot of misunderstanding contained in some posts about fan systems, so let me help clear things up.

Almost all fan headers on mobos can supply up to 1.0 amps current in total to all the fans connected to that one header. On some newer mobos now I am seeing special headers labelled H_AMP_FAN that can supply up to 3.0 amps, but they are not the "common" ones. Your mobo says its CPU_FAN header can supply up to 2.0 amps, but that does NOT apply to the CHA_FAN header.

Your mobo has three fan headers, and each does a different job, so don't confuse them. The CPU_FAN header normally is used only for power and control of the cooler for your CPU chip. It is based on a temperature sensor inside the CPU chip itself that feeds a signal to the mobo on one pin of the chip. The PWR_FAN header very likely is of no use to you. It is intended solely for use when your PSU has a special set of three wires coming out that end in a female 3-pin fan connector that can plug into the PWR_FAN header. Is only function is supposed to be to allow your PSU to send its fan's speed signal to your mobo so it can be displayed. The intent is that, if your PSU does not have this set of signal leads, you connect NOTHING to the PWR_FAN header. Now, it happens that the mobo actually does have Ground and a fixed +12 VDC on its first two pins, so it CAN be used to provide power to a fan, BUT there will be no control available - it will always run the fan at full speed. The header of interest for this thread is the CHA_FAN header. Its fan control is tied to a different temperature sensor built into the mobo, so it is the place to connect case ventilation fans.

There are two basic types of fan designs used widely in computers now. 3-pin fans are older. The signals on the mobo header being fed to the fan are Ground (Black wire) on Pin #1, +DCV (red wire) on Pin #2, and Speed Pulses (Yellow wire) on Pin #3. The voltage on Pin #2 is varied by the mobo, from 12 VDC max down to about 5 VDC min usually, to control the fan's speed. The fan motor itself generates a speed signal of two pulses per revolution and sends that back to the mobo on Pin #3. The mobo can display that for you and will monitor it for failure detection. But it does not actually USE that signal to control the fan speed.

The newer system is 4-pin fans. Mechanically and electrically the signals and pins are very similar, so you CAN connect any 3-pin fan to any 4-pin header, and the other way around. The fan will work, but with some limitations when you mis-match them. The header for a 4-pin fan IF it actually uses the true 4-pin PWM method of control, has these signals (not mentioning colours here because they are different from 3-pin system): Pin #1 is Ground again, Pin #2 is a fixed +12 VDC, Pin#3 is for the Speed Pulse signal again, and the added Pin #4 is the PWM signal going to the fan motor. Inside fans of this type there is a small chip that uses the PWM signal to modify the flow of current from Pin #2 to the motor windings, turning it on and off very quickly (at about 20 kHz) to reduce the average current through the motor and thus changing its speed.

Now, what happens if you mis-match fan type to header type? Plug a 3-pin fan into a 4-pin header and the fan receives a fixed 12 VDC on Pin #2 at all times, but it does not receive (nor could it use) the PWM signal, so the fan always runs full speed. It cools, but there's no control. The other way: plug a 4-pin fan into a 3-pin header. That fan does not receive any PWM signal so its internal chip cannot modify the power supplied on Pin #2. BUT that pin is supplying a VARYING voltage, so the fan's speed DOES change, and the mobo can control it. This form of control of a 4-pin fan is not ideal, but it works.

Here's where a lot of confusion can start. First, any 3-pin fan header can ONLY operate in the older Voltage Control Mode. On MANY mobos now the fan headers all have 4 pins, but they do not always work as 4-pin headers! Some actually use only the 3-pin method called Voltage Control Mode or DC Mode for control, and never send out a PWM signal on Pin #4. As you can see from above, this WILL accomplish speed control of either design of fan, so it's kind of "universal" even though it fails to use the advantages of the new PWM fan design. This type of header does cause a problem, though, if you are trying to use a 4-pin Hub to connect several fans to one header, because such devices MUST have a PWM signal on Pin #4.

On better mobos today you often will find that in BIOS Setup you are given a choice of how a mobo fan header controls its fans. You can set whether it uses the older Voltage Control Mode (aka DC Mode) or the newer PWM Mode. A few even claim that they are self-configuring and can automatically detect which type of fan is connected and set themselves.

One more background point which actually IS pertinent to your case. A mobo header can accept and handle the speed pulse signal from only ONE fan on Pin #3. So, any proper Splitter or Hub will only send back to the header ONE fan's speed signal, and not connect the other one. Some earlier Splitters were made wrong and connected both fan's signals back to the mobo, causing them to get very confused with double the pulses coming in and at wildly changing timings. The Splitter you gave a link to is done this wrong way (as you say, it has all pins on both outputs) and that is why your mobo is showing you wildly swinging speed readings when you use it with two fans. I'll outline a fix later.

Your mobo has only one CHA_FAN header to use. In the manual on p. 1-27 the label on Pin #4 is not at all clear, and there is no other clear statement about the control method this header uses. However, both of those Coolermaster fans are true 4-pin units, so they CAN be powered and controlled by either type of mobo header. Moreover, they each are spec'd at 0.26 amps, so the total load is 0.52 amps, and there is no problem connecting both of them to a single header using a Splitter.

The last problem is the construction of your Splitter and the way it is causing fluctuating fan speed readings. You can fix this by cutting one of the wires to Pin #3 of one of the output arms. You'll have to slit back the outer covering a little to get to it. When you're done, ensure the end connected back to the female connector (the one that plugs into the mobo) is not able to short out some place. To identify which wire, look at the output connectors. There is a plastic "tongue" on one side aligned with the first three pins, and a gap over the 4th pin. So you can identify Pin #3 and snip the wire doing to that pin on ONE of the two male output connectors. You will never "see" the speed of the fan plugged into that one, but that's OK.

The mobo does NOT try to control the speeds of all the fans on a header to be the same. In fact, as I said, it does not even worry what the speed is (except for failure detection, which is not part of speed control). The header simply sends a power supply on Pin #2 and a PWM signal on Pin #4 and whatever speed that delivers in any fan is OK as far as the mobo is concerned. If they don't match because the two fans are of different designs, it does not care. In fact, the truth is that the automatic fan control systems are NOT paying attention to fan speed. The are trying to ensure that the TEMPERATURES at the relevant sensors are correct, and they merely change the power going out to their fans to alter the cooling they give, thus keeping the temperatures under control.

 

[artey1498]

I can understand how you got confused. There is a lot of misunderstanding contained in some posts about fan systems, so let me help clear things up.

Almost all fan headers on mobos can supply up to 1.0 amps current in total to all the fans connected to that one header. On some newer mobos now I am seeing special headers labelled H_AMP_FAN that can supply up to 3.0 amps, but they are not the "common" ones. Your mobo says its CPU_FAN header can supply up to 2.0 amps, but that does NOT apply to the CHA_FAN header.

Your mobo has three fan headers, and each does a different job, so don't confuse them. The CPU_FAN header normally is used only for power and control of the cooler for your CPU chip. It is based on a temperature sensor inside the CPU chip itself that feeds a signal to the mobo on one pin of the chip. The PWR_FAN header very likely is of no use to you. It is intended solely for use when your PSU has a special set of three wires coming out that end in a female 3-pin fan connector that can plug into the PWR_FAN header. Is only function is supposed to be to allow your PSU to send its fan's speed signal to your mobo so it can be displayed. The intent is that, if your PSU does not have this set of signal leads, you connect NOTHING to the PWR_FAN header. Now, it happens that the mobo actually does have Ground and a fixed +12 VDC on its first two pins, so it CAN be used to provide power to a fan, BUT there will be no control available - it will always run the fan at full speed. The header of interest for this thread is the CHA_FAN header. Its fan control is tied to a different temperature sensor built into the mobo, so it is the place to connect case ventilation fans.

There are two basic types of fan designs used widely in computers now. 3-pin fans are older. The signals on the mobo header being fed to the fan are Ground (Black wire) on Pin #1, +DCV (red wire) on Pin #2, and Speed Pulses (Yellow wire) on Pin #3. The voltage on Pin #2 is varied by the mobo, from 12 VDC max down to about 5 VDC min usually, to control the fan's speed. The fan motor itself generates a speed signal of two pulses per revolution and sends that back to the mobo on Pin #3. The mobo can display that for you and will monitor it for failure detection. But it does not actually USE that signal to control the fan speed.

The newer system is 4-pin fans. Mechanically and electrically the signals and pins are very similar, so you CAN connect any 3-pin fan to any 4-pin header, and the other way around. The fan will work, but with some limitations when you mis-match them. The header for a 4-pin fan IF it actually uses the true 4-pin PWM method of control, has these signals (not mentioning colours here because they are different from 3-pin system): Pin #1 is Ground again, Pin #2 is a fixed +12 VDC, Pin#3 is for the Speed Pulse signal again, and the added Pin #4 is the PWM signal going to the fan motor. Inside fans of this type there is a small chip that uses the PWM signal to modify the flow of current from Pin #2 to the motor windings, turning it on and off very quickly (at about 20 kHz) to reduce the average current through the motor and thus changing its speed.

Now, what happens if you mis-match fan type to header type? Plug a 3-pin fan into a 4-pin header and the fan receives a fixed 12 VDC on Pin #2 at all times, but it does not receive (nor could it use) the PWM signal, so the fan always runs full speed. It cools, but there's no control. The other way: plug a 4-pin fan into a 3-pin header. That fan does not receive any PWM signal so its internal chip cannot modify the power supplied on Pin #2. BUT that pin is supplying a VARYING voltage, so the fan's speed DOES change, and the mobo can control it. This form of control of a 4-pin fan is not ideal, but it works.

Here's where a lot of confusion can start. First, any 3-pin fan header can ONLY operate in the older Voltage Control Mode. On MANY mobos now the fan headers all have 4 pins, but they do not always work as 4-pin headers! Some actually use only the 3-pin method called Voltage Control Mode or DC Mode for control, and never send out a PWM signal on Pin #4. As you can see from above, this WILL accomplish speed control of either design of fan, so it's kind of "universal" even though it fails to use the advantages of the new PWM fan design. This type of header does cause a problem, though, if you are trying to use a 4-pin Hub to connect several fans to one header, because such devices MUST have a PWM signal on Pin #4.

On better mobos today you often will find that in BIOS Setup you are given a choice of how a mobo fan header controls its fans. You can set whether it uses the older Voltage Control Mode (aka DC Mode) or the newer PWM Mode. A few even claim that they are self-configuring and can automatically detect which type of fan is connected and set themselves.

One more background point which actually IS pertinent to your case. A mobo header can accept and handle the speed pulse signal from only ONE fan on Pin #3. So, any proper Splitter or Hub will only send back to the header ONE fan's speed signal, and not connect the other one. Some earlier Splitters were made wrong and connected both fan's signals back to the mobo, causing them to get very confused with double the pulses coming in and at wildly changing timings. The Splitter you gave a link to is done this wrong way (as you say, it has all pins on both outputs) and that is why your mobo is showing you wildly swinging speed readings when you use it with two fans. I'll outline a fix later.

Your mobo has only one CHA_FAN header to use. In the manual on p. 1-27 the label on Pin #4 is not at all clear, and there is no other clear statement about the control method this header uses. However, both of those Coolermaster fans are true 4-pin units, so they CAN be powered and controlled by either type of mobo header. Moreover, they each are spec'd at 0.26 amps, so the total load is 0.52 amps, and there is no problem connecting both of them to a single header using a Splitter.

The last problem is the construction of your Splitter and the way it is causing fluctuating fan speed readings. You can fix this by cutting one of the wires to Pin #3 of one of the output arms. You'll have to slit back the outer covering a little to get to it. When you're done, ensure the end connected back to the female connector (the one that plugs into the mobo) is not able to short out some place. To identify which wire, look at the output connectors. There is a plastic "tongue" on one side aligned with the first three pins, and a gap over the 4th pin. So you can identify Pin #3 and snip the wire doing to that pin on ONE of the two male output connectors. You will never "see" the speed of the fan plugged into that one, but that's OK.

The mobo does NOT try to control the speeds of all the fans on a header to be the same. In fact, as I said, it does not even worry what the speed is (except for failure detection, which is not part of speed control). The header simply sends a power supply on Pin #2 and a PWM signal on Pin #4 and whatever speed that delivers in any fan is OK as far as the mobo is concerned. If they don't match because the two fans are of different designs, it does not care. In fact, the truth is that the automatic fan control systems are NOT paying attention to fan speed. The are trying to ensure that the TEMPERATURES at the relevant sensors are correct, and they merely change the power going out to their fans to alter the cooling they give, thus keeping the temperatures under control.

Thanks for taking the time to write a well-detailed post to clear up the confusion. So basically, using the splitter is indeed fine, and moreover, the fact that they are different sized fans doesn't matter because the mobo is not paying attention to the speeds, right? I'll go ahead and do what you outlined in regards to the splitter as well, however I have a question regarding plugging a 3-pin fan into a 4-pin header. You mentioned it would receive a fixed voltage of 12v and run at full speed, however I have a spare 3-pin fan that I plugged into the 4-pin header and it only runs at about 50% speed. I even tested plugging the fan to a molex cable and it was much louder that time (sounded like a weed-whacker). Regarding how to fix the splitter issue, once I snipped wire #3 would that make the fan run at full speed, or would it continue to run at 50%?

Also, I think I'm now having an overheating issue with my computer. I'm unsure of whether or not I should make a new thread for this, because I think it could be related to the splitter somehow. Lately the 92mm fan has been a bit loud (even on idle), with the idle rpm around 1,600+ it seems when it used to be like 1,300. I put my hand behind my computer and felt a lot of air being moved by both the case fan and the psu fan. The 80mm intake fan continues to run (at what seems like) 50% speed, however. I launched Left 4 Dead 2 yesterday and played an online match, and after about 10 minutes my computer turned into a jet turbine pretty much. All my fans (except the intake I think) were pretty much at max rpm. It was the loudest I've ever heard it. I checked my cpu's max temp (using core temp) and it was 58 c (my cpu's max temp is 70c). Before I installed the splitter the max was like 54c under load. The ambient room temp was about 20c. I tried unplugging the splitter and intake fan and plugged the exhaust fan directly into the motherboard header, and it still was on the loud side. Do you know what's going on? On idle all my temps are fine (in the ~30c range). I fully cleaned out my computer only 3 days ago, so it's definitely not a dust issue. I hate to ask a billion questions on this one thread but I'm just about hanging on to my last thread of sanity with this computer.

 

[Paperdoc]

Second query first. If you snip of the lead to Pin #3 of ONE output arm of the splitter, that won't change the way the fan is controlled. All that will do is prevent the confusion the mobo is experiencing now because of two fan speed signals overlapping.

You speak of a "spare 3-pin fan" and of an 80 mm fan mounted as front intake. Are those two different fans, or just the same one?

You linked to a mobo web page but then commented that your actual mobo is a slightly different model with "two headers". The manual in the link has three headers in total, one each of three types as I outlined above. Does yours actually have a FOURTH header? Or THREE? what are their labels?

Then you say you plugged that "into a 4-pin header". What header? As I said, the manual says your mobo has only one CHA_FAN header and it has 4 pins and appears to be using true 4-pin PWM Mode. So, are both the 92 mm 4-pin PWM unit and the 3-pin 80 mm fan connected to that one CHA_FAN header by using the Splitter?

If a 3-pin fan is plugged into a 4-pin header that actually is using PWM Mode for control, then it will only run at full speed. However, you say when plugged into "a 4-pin header" it appears to run at only half speed, and when plugged into a PSU output it runs noticeably faster. Again, I wonder what 4-pin header? And, how is that header configured in BIOS Setup? There could be a setting that limits its speed, or it could be using the wrong temperature sensor.

If you connect both of your 4-pin Coolermaster fans (80 and 92 mm) to the Splitter and thereby to the CHA_FAN header, they both should change their speeds together. Doing that with that Coolermaster 80 mm unit at the front would then improve things.

Now another idea to consider. Do you have room in the case front to mount both of your 80mm fans? Since you seem to have somewhat inadequate cooling now, this could improve that. You mount both in the front as intakes. Connect the 3-pin spare one to that "PWR_FAN" header I told you not to use. Then it will run at full speed all the time because that header does no control. Connect the two Coolermaster PWM fans (80 mm front intake, 92 mm rear exhaust) via the modified splitter to the CHA_FAN header and their speeds will be automatically controlled by the mobo. You'll get a sort of "base level" ventilation with the full-speed 3-pin fan plus controlled additional ventilation from the other two.

 

[artey1498]

Second query first. If you snip of the lead to Pin #3 of ONE output arm of the splitter, that won't change the way the fan is controlled. All that will do is prevent the confusion the mobo is experiencing now because of two fan speed signals overlapping.

You speak of a "spare 3-pin fan" and of an 80 mm fan mounted as front intake. Are those two different fans, or just the same one?

You linked to a mobo web page but then commented that your actual mobo is a slightly different model with "two headers". The manual in the link has three headers in total, one each of three types as I outlined above. Does yours actually have a FOURTH header? Or THREE? what are their labels?

Then you say you plugged that "into a 4-pin header". What header? As I said, the manual says your mobo has only one CHA_FAN header and it has 4 pins and appears to be using true 4-pin PWM Mode. So, are both the 92 mm 4-pin PWM unit and the 3-pin 80 mm fan connected to that one CHA_FAN header by using the Splitter?

If a 3-pin fan is plugged into a 4-pin header that actually is using PWM Mode for control, then it will only run at full speed. However, you say when plugged into "a 4-pin header" it appears to run at only half speed, and when plugged into a PSU output it runs noticeably faster. Again, I wonder what 4-pin header? And, how is that header configured in BIOS Setup? There could be a setting that limits its speed, or it could be using the wrong temperature sensor.

If you connect both of your 4-pin Coolermaster fans (80 and 92 mm) to the Splitter and thereby to the CHA_FAN header, they both should change their speeds together. Doing that with that Coolermaster 80 mm unit at the front would then improve things.

Now another idea to consider. Do you have room in the case front to mount both of your 80mm fans? Since you seem to have somewhat inadequate cooling now, this could improve that. You mount both in the front as intakes. Connect the 3-pin spare one to that "PWR_FAN" header I told you not to use. Then it will run at full speed all the time because that header does no control. Connect the two Coolermaster PWM fans (80 mm front intake, 92 mm rear exhaust) via the modified splitter to the CHA_FAN header and their speeds will be automatically controlled by the mobo. You'll get a sort of "base level" ventilation with the full-speed 3-pin fan plus controlled additional ventilation from the other two.

Thanks for clarifying. They're two seperate fans. Both are 80mm, however. The mobo that came with my pc is actually (I think) a special variant of the F2ABB-M motherboard, with only two headers: one labeled CPU_FAN and one labeled CHA_FAN. The mobo in my original post is almost as close to my motherboard as possible, save for the headers. The 4 pin header I was speaking of was the CHA_FAN header. Yes, I tried plugging both 92mm 4-pin and 80mm 3-pin fans into the splitter. The 80mm fan seemed to only run at 50% speed (it was definitely not full speed) when I did so. I checked the bios, and I didn't see any options to change the header type or anything. I did see the options to change what fan setting modes to use for the CPU and CHA fans (basically it was a toggle of the PWM control). I actually do not have more room for the third fan, I wish I did but there's only two grills in my case, and I'm not entirely comfortable with making a custom spot for one (don't want to mess something up). I DO have my front case panel cracked ajar, however, because it's just a solid piece of plastic and doesn't have any type of airflow for the front intake fan. Eventually I'm going to just drill a few holes into it and call it quits (I am cautious about doing so).

My computer is about 3-4 years old, and before last month I never had any case fans for it (although I did have it set up in a basement for a while), so I'm theorizing that maybe my cpu is about to croak or something.

I should have clarified all of this in my original post, my bad.

 

[artey1498]

Yesterday I tidied up the fans in my case a bit more, and cut the speed wire (#3) on one of the splitter ends, like you suggested. I put some electrical tape on both of the cut ends, however I wasn't able to put the tape on too tight, due to the wire being so small and hard to grasp. I'm hoping that I did a good enough job. When I first booted the pc after cutting the wire, my computer got stuck on the boot screen and refused to boot. I then unplugged a usb wifi-adapter I had plugged in and it booted normally. Looks like the splitter is working fine (knock on wood), but now I think I'm getting electrical interference or something from my speakers; there's a buzzing sound coming from them, which wasn't there before I cut the wire, I think. I am using the 3-pin case fan and it is still running at roughly 50% speed.

Update: The buzzing sound that I was hearing has apparently stopped (knock on wood).

 

[Paperdoc]

Glad to hear it's working for you.