Question Splitting the CPU fan header - potential issues?

poguesquadron

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(Trying to post this for the second time so I'll try to keep it brief)
My upcoming build has two fan headers on the motherboard (MSI B450i Gaming Plus AC), but I have four total fans - one for the CPU (Noctua U12s using a Noctua NF-F12 fan), and three case fans (Corsair LL 120mm RGB).

After going back and forth on how to do this, I've decided I don't exactly want to bring in a hub or controller into the build. If I use a splitter, can I split the CPU fan header between the CPU cooler and the rear case fan? From what I've read, this would cause the rear case fan to basically be bound to the CPU fan in terms of its behavior. I've checked that amp wise, this all should work fine. The Noctua only uses .05A, and the Corsair fan .3A. Each header uses 1A.

Is this unheard of? I guess this setup would basically just cause the rear fan to rev up whenever the CPU fan revs up, which I don't see as an issue. Still, I want to make sure that this isn't frowned upon, or is something I should avoid.

If this is something I should avoid, I think I may be only using two of the case fans, and either sell the one I'm not using, or put it to the side until I work out some kind of hub situation. Does anyone have experience with this? I'm sure it has to be something ITX builders come across, hopefully. Thanks in advance!

tldr; Is it bad to split the CPU header between the CPU cooler and a case fan?
 
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From what I've seen, CPU coolers that have 2 fans attached to it use a splitter by default, so most likely it would perform the same way, but with the fan being mounted to the back instead. In my limited experience I haven't heard of anyone doing this, but I also can't think of a reason why it wouldn't work. All I would look out for is making sure that when it does rev up, it's not blowing out more air than the intakes can pull in, creating a negative air pressure
 
You can do whatever you want, except the difference, is it PWM controlled or DC controlled.
Just beware of that.
DC is + and - doing square wave (Same/similar to Switching frequency),
while PWM control is via switching frequency while keeping max voltage.

Also to add PWM has 4 wires ,while DC is 3pin (3rd pin is fan speed).
 
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poguesquadron

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Yeah I have to say, I'm a little stumped as to how to proceed here. In some of the build guides I've seen on YouTube, builders have just used a rear case fan, a front case fan, and the CPU cooler and have been fine with temps. If adding the third fan won't necessarily help things, maybe I can just go in that direction.

I feel like my options are:
  • Split the CPU header - rear case fan and CPU fan operate similarly. But this would create a lot of airflow at the exhaust end of the case.
  • Split the case fan header - but then my exhaust and intake fans on the rear and front of the case are on the same header and can't operate independently.
  • SKIP a rear fan altogether and if I can, put two case fans as intake on the front and bottom. That way, the front of the case naturally has more air coming in. The Noctua would then exhaust the air out the back of the case. But then I don't know if that's enough exhaust?
This was a lot easier 9 years ago when I just moved the switch on my case fans from medium to low, lol. Maybe I'm overcomplicating things?
 

rickypicky5

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Yeah I have to say, I'm a little stumped as to how to proceed here. In some of the build guides I've seen on YouTube, builders have just used a rear case fan, a front case fan, and the CPU cooler and have been fine with temps. If adding the third fan won't necessarily help things, maybe I can just go in that direction.

I feel like my options are:
  • Split the CPU header - rear case fan and CPU fan operate similarly. But this would create a lot of airflow at the exhaust end of the case.
  • Split the case fan header - but then my exhaust and intake fans on the rear and front of the case are on the same header and can't operate independently.
  • SKIP a rear fan altogether and if I can, put two case fans as intake on the front and bottom. That way, the front of the case naturally has more air coming in. The Noctua would then exhaust the air out the back of the case. But then I don't know if that's enough exhaust?
This was a lot easier 9 years ago when I just moved the switch on my case fans from medium to low, lol. Maybe I'm overcomplicating things?
I would buy a 3-way splitter and:
  • Split the case fan header - but then my exhaust and intake fans on the rear and front of the case are on the same header and can't operate independently.
3-way splitter
 
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poguesquadron

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That's basically what I wound up doing, but I wound up getting a hub to put all three case fans on. This leaves the CPU fan on its own header. This should also give me some flexibility if I ever populate the case's fourth and final case fan. Hopefully it works out okay :)
 

rickypicky5

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That's basically what I wound up doing, but I wound up getting a hub to put all three case fans on. This leaves the CPU fan on its own header. This should also give me some flexibility if I ever populate the case's fourth and final case fan. Hopefully it works out okay :)
That's what I meant - use the 3-way splitter, for your 2 front fans plus the rear fan, connected to the SYS fan header on the motherboard, and use the CPU fan header for the CPU fan. I think you'll be fine.
 

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