Question Connecting a fan splitter to AIO header

jackman9061

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Jan 31, 2018
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I'm using a pretty small case for my build (Fractal Design Nano S), and I want to connect more fans to my case to increase airflow. Only problem is that I can only plug 2 fans into the fan splitter that is connected to my Chassis fan header, and I want to connect a few more fans, by using the AIO Fan header. So can I do this safely? My motherboard is the Asus ROG Strix X470-I Gaming.
 

Karadjgne

Titan
Herald
Depends on the fans and what you have now. If the 2 existing fans are 3pin, 2 is the recommended maximum. You have upto 1A (12w) capacity on the header and DC fans usually take more juice to power. If you have pwm fans, with a sata/molex powered splitter/hub you can add upto 10 fans on the one header, the limitation doesn't apply since it's external power, but the pwm signal gets too weak after 10 branches. Otherwise 3 pwm is the usual limit.

As far as powering from the aio header, same thing applies, either 2 or 3 if power from header.

For DC 3pin fans, to get more than 2 usually requires some sort of powered controller, most are 4 - 6way and handle upto @ 30w total.
 
Using a Splitter to connect more than one fan to a single header is limited by the header's max current available, which in your case is 1.0 A total from EACH header. So you need to know the max current spec of each fan you propose to use this way. Many common case vent fans use 0.2 A or less, so even 4 can be done, BUT it depends entirely on what the fan specs say. And be aware that LED fans - the ones with a single colour of lights in the frame, not the many-changing-colours type - use MORE current than a plain fan. IF your fans are of the 3-pin type, their speeds can ONLY be controlled by a mobo header that uses the older DC Mode (a choice you do have available in your fan header configurations), and that also REQUIRES that you use a SPLITTER for grouping them, and not a HUB.

A HUB is a different device and can avoid the current limit of a header. But it can be used to control fan speeds ONLY if the fans all are 4-pin PWM type, and ONLY if the mobo header is configured to use the newer PWM Mode of control.

Your thread asks about using the mobo AIO_PUMP header for case vent fans. The answer is MAYBE, because some of the factors are not detailed in the mobo manual.

1. Most fan headers do exercise speed control of their fans, and your mobo's headers can be configured to do this using either the new PWM Mode (for 4-pin fans) or the older DC Mode (for 3-pin fans). My question is whether or not your mobo does this also for its AIO_PUMP header. You see, most AIO systems are designed to run the pump at full speed all the time. So IF your mobo actually restricts that particular header to providing NO speed control, then it can't work for you. BUT if the header acts "normally", then you're going to be OK. How can you tell? A simple test can do that once you have the system assembled. The normal start-up sequence for fans is that they always start up at full speed and then, after a few seconds, the mobo automatic speed control system slows the fans down to whatever is needed for the cool system. So, you can open your case, ensure that one 4-pin case fan is plugged into that AIO_PUMP header, and watch it carefully right as you start the system. If it starts up fast then slows down, your system IS exerting automatic speed control and you can use it as a "normal" fan header. Now shut down and re-connect your fans as you need.

2. Since the AIO_FAN header is intended for use as part of a CPU chip cooling system, it is very likely that any control it does do is based on a temperature sensor inside the CPU chip. Now, case fan speed ideally should be based on a different temp sensor on the mobo, but there does not appear to be any way to set the AIO_PUMP header to use that sensor. So the speeds of your fans attached to that header will be based on the CPU internal temperature. While not ideal, this is a pretty good way because there is a good correlation between CPU heat and workload, and overall system (motherboard etc.) heat generation and cooling needs.
 

jackman9061

Prominent
Jan 31, 2018
40
1
545
1
Using a Splitter to connect more than one fan to a single header is limited by the header's max current available, which in your case is 1.0 A total from EACH header. So you need to know the max current spec of each fan you propose to use this way. Many common case vent fans use 0.2 A or less, so even 4 can be done, BUT it depends entirely on what the fan specs say. And be aware that LED fans - the ones with a single colour of lights in the frame, not the many-changing-colours type - use MORE current than a plain fan. IF your fans are of the 3-pin type, their speeds can ONLY be controlled by a mobo header that uses the older DC Mode (a choice you do have available in your fan header configurations), and that also REQUIRES that you use a SPLITTER for grouping them, and not a HUB.

A HUB is a different device and can avoid the current limit of a header. But it can be used to control fan speeds ONLY if the fans all are 4-pin PWM type, and ONLY if the mobo header is configured to use the newer PWM Mode of control.

Your thread asks about using the mobo AIO_PUMP header for case vent fans. The answer is MAYBE, because some of the factors are not detailed in the mobo manual.

1. Most fan headers do exercise speed control of their fans, and your mobo's headers can be configured to do this using either the new PWM Mode (for 4-pin fans) or the older DC Mode (for 3-pin fans). My question is whether or not your mobo does this also for its AIO_PUMP header. You see, most AIO systems are designed to run the pump at full speed all the time. So IF your mobo actually restricts that particular header to providing NO speed control, then it can't work for you. BUT if the header acts "normally", then you're going to be OK. How can you tell? A simple test can do that once you have the system assembled. The normal start-up sequence for fans is that they always start up at full speed and then, after a few seconds, the mobo automatic speed control system slows the fans down to whatever is needed for the cool system. So, you can open your case, ensure that one 4-pin case fan is plugged into that AIO_PUMP header, and watch it carefully right as you start the system. If it starts up fast then slows down, your system IS exerting automatic speed control and you can use it as a "normal" fan header. Now shut down and re-connect your fans as you need.

2. Since the AIO_FAN header is intended for use as part of a CPU chip cooling system, it is very likely that any control it does do is based on a temperature sensor inside the CPU chip. Now, case fan speed ideally should be based on a different temp sensor on the mobo, but there does not appear to be any way to set the AIO_PUMP header to use that sensor. So the speeds of your fans attached to that header will be based on the CPU internal temperature. While not ideal, this is a pretty good way because there is a good correlation between CPU heat and workload, and overall system (motherboard etc.) heat generation and cooling needs.
Ok, I'll give it a shot, I was just worried I might damage something (either the fans or the motherboard itself). Only one of the fans I plan on connecting to the splitter is PWM, the other one is a 3-pin fan that came with the PC case.
 
Wait! The starting point of this that actually contributes to your problem is that you say you already have 2 fans on the mobo CHA_FAN header, and believe you cannot add more to that header. Well, the SAME considerations apply to the AIO_PUMP header: each is limited to 1.0 A max current. So, IF your calculations show that you can afford to connect three or four fans to one of those headers, that also means you COULD do that via the CHA_FAN header.

I point this out because you say your plan is to MIX a 3-pin and a 4-pin fan on one header. Those two types of fans require DIFFERENT methods of controlling them. That is what the MODE option in a fan header configuration is about. Ideally, you set it to DC Mode for 3-pin fans,and PWM Mode for 4-pin fans. For a 3-pin fan the DC Mode is the ONLY way to control its speed - using PWM Mode with that will cause the 3-pin fan to run full speed always. For 4-pin fans, although they are best done with the new PWM Mode, they actually CAN have their speed controlled by the DC Mode, so that IS one way you can "MIX" the two fan types on one header set to DC Mode.

On the other hand, you can use the optimal fan header MODE for each type if you group them correctly. Arrange all your 3-pin case vent fans on one Splitter and header that is configured to DC Mode. Arrange all your 4-pin case vent fans similarly on a different header and configure it to use PWM Mode.

IF your calculations confirm you can do those groups within the amp limit of each header, then you just need a couple of Splitters to do that. Most Splitters today are of the 4-pin variety, but that will work for BOTH fan types. BUT the common Splitters have only two output arms. If you have more to group, there are three ways.

1. Using only 2-output Splitters, you buy three of them and build a "stack" by plugging two of them into the output arms of the third. This converts one mobo header into four fan outputs.

2. Buy a three-output Splittter like this

https://www.newegg.com/p/N82E16812423163?Description=coboc fan splitter&cm_re=coboc_fan_splitter-_-12-423-163-_-Product

3. Buy a 4-output Splitter like this

https://www.newegg.com/p/N82E16882422016?Description=coboc fan splitter&cm_re=coboc_fan_splitter-_-82-422-016-_-Product

It looks like a small circuit board rather than a group of cable arms. I should be fastened down so it does not move and risk shorting out to Ground. One of its ports is labelled for the CPU fan, but ignore that. That is just the only output port that DOES send its fan's speed signal back to the mobo header. On the "group of arms" styles above, the only output that sends back the speed signal is the one with all four pins - the others skip the speed signal by NOT having a Pin #3.

So you can create using Splitters two groups according to fan type (3-pin or 4-pin), and use both the AIO_PUMP header and the CHA_FAN header for all those case fans. Then you can configure each header to the best control MODE for each type of fan.
 
You can do that IF you configure that CPU_FAN header to use the older Voltage Control Mode (aka DC Mode) so that it can control the speed of both fan types, and IF the max total load on that header is less than 1.0 A. IF you can't work within that current limit on one header, or IF you want to use the optimal methods of control for 3-pin and 4-pin fans separately, use two headers configured differently.
 

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