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PWM or DC fan headers

So I have a corsair h60 for my cpu header. I have 3 other fans hooked up to sys fan headers. They are all 3 pins. In the bios I can switch them to pwm and they just run full speed. I'm fine with this but I'm wondering if there is a limit to how many fans you should set to pwm. Could it cause problems? Same with DC, does it matter how many fans run on it? I have a z270 a pro board if that matters.
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  1. Best answer
    Yes. Each fan header is supposed to be rated at 1A. Crappy fans can be rated at as much as 0.5A, but good fans can be as low as 0.2A. The amperage rating is almost always printed on the back of the fan. If wattage, such as 3w, divide by 12 to get the A.

    So you can ostensibly run @2-4 fans per header on unpowered splitters.

    Does not matter how many fans are set to what, each header has its own amperage rating.

    DC (analog) is voltage controlled, is almost always 3pin, but can be 4pin or molex. Speeds are regulated by input voltage ranging from 12v max speed to 5v or 7v minimum, or about 40% or 60% ratings.

    PWM is different. It runs constantly at 12v. The Pulse Modulation turns the fan on/off at variable rates, so unless at full speed, the fan is in a constant state of trying to spin all the way up.

    Cpu_fan header is a dedicated PWM header, not changeable to analog.

    Corsair directions state the aio pump connected to cpu_fan header (this automatically applies a constant 12v to the pump) and the fan to a sys_fan header.
    I personally find that a pain as there's a big difference in case temps and cpu temps, so the cpu fan won't respond correctly to changing cpu temps. I hook the pump to any header (cpu-aux is good) and in bios permanently set the duty cycle at 100%, so there's no voltage variation. Fan goes on cpu_fan, so there's normal fan control with a Pwm fan.
  2. To the best of my knowledge fan headers can handle about 1A at 12V. How many fans you can place would depend on the draw of each fan at full load. As for number of fans. There really is no practical limit. You can get powered PWM splitters to place numerous fans off one header. The powered splitter draws its power directly from the PSU using a Molex connector or SATA connector. All it gets from the motherboard is the PWM signal.

    In your case. You are using 3-pin fans. So, no PWM for you. 3-pin uses voltage regulation while 4 pin uses a signal to the fan to control speed. If your motherboard supports it. You can switch from PWM to voltage or analog in the BIOS settings.
    https://noctua.at/en/can-i-run-noctua-3-pin-fans-on-4-pin-pwm-connectors-and-use-my-mainboards-automatic-fan-controller
    If it doesn't you'll need a fan speed controller.

    Karadjgne said:
    Yes. Each fan header is supposed to be rated at 1A. Crappy fans can be rated at as much as 0.5A, but good fans can be as low as 0.2A. The amperage rating is almost always printed on the back of the fan. If wattage, such as 3w, divide by 12 to get the A.


    I wouldn't call Noctua iPPC-3000 NF-A14 crappy. They draw 0.55A.
    https://noctua.at/en/nf-a14-industrialppc-3000-pwm/specification
  3. So for the fans on pwm, I should just set to full speed?
  4. I hve a 120mm insignia fan, which is the only fan I cant find wattage info for online or elsewhere.
  5. ^ doesnt matter - its the 4th wire that controls the pwm signal
    On a 3 pin fan its missing so what you set pwm ratio at is irrelevant..

    Ampage should be on the label on the fan itself, every fan Ive ever seen (even $2 ones) have that info somewhere on them.
  6. So I have some fans running on 10.56 v and some around 11.04 v. Theres no reason not to run things at certain voltages are there? I mean like in between 12v it doesn't matter right?
  7. There is a sweet spot in some AIO water coolers pump speed around 80% that reduces it's noise level by almost 50%, not all the pumps and CPU headers allow this, working for me on Asus Z270E with thermaltake water 3.0 360 Riing.
  8. I meant the regular 120mm fans not the pump
  9. DC fans will only run within limits. Most crappy fans will only go down to 7v (@60%), most better fans will go as low as 5v (@40%) which will be translated to fan rpm. A 2000rpm good fan will therefore operate at @800rpm-2000rpm ± 10%. A junky 2000rpm fan will be @1200rpm-2000rpm ±10%. Very big difference in volume at idle speeds, max speed volume will be determined by the fans, good fans tend to be quieter.

    And yes, that Noctua pulls 0.55A, but it's also an industrial grade fan able to run at 3000rpm, not a standard pc case fan which generally fall into the 1000-2000rpm range. By comparison, to the Delta 5200rpm 120mm fan, that'll pull a max of 3.25A, so definitely not recommended for a mobo header usage. Above a certain point, things do change.

    Noctua NF-F12 I own pulls 0.18A @1500rpm, and thats a 6yr old fan, it's been revamped since then.
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