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Why is it not recommended to connect two fans to CPU header?

Last response: in Overclocking
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February 8, 2011 8:40:36 AM

Hi,

I have a noctua 9B CPU cooler, which comes with two fans and a splitter to connect to one CPU header. But reading up, I keep hearing over and over that you should only connect one fan per header, concern about overloading the motherboard etc. I'm new to this building lark, so I'm wary to go against such repeated advice.

But.


First, Noctua (who seem to be a recommended manufacturer) give you a splitter. Why would they do that if it wasn't meant to be used?

Second, the CPU header on my ASUS P8P67 is rated for 12W/1A. The Noctua fans on the CPU cooler are rated at 1.32W each. So a total of 2.64W/0.22A. Even if thats normal power, and they need double on startup, thats only 5.28W/0.44A - still less than half the rated power of the CPU fan header.

I don't see where the concern is, but as I'm new to this I'm wary of going against advice.
a b à CPUs
a b K Overclocking
February 8, 2011 10:33:32 AM

technically its better to connect one fan per header for safeguarding your mobo... two fans fed on one 12v supply will result in more power drawn from the boards header leading to a slight overload on the mobo... I have generally found this OK and within operating norms but what i did to be on the safer side was to swap the fans for PWM fans and then getting this splitter... what this does is the power is drawn from the psu but the speed modulations are got from the mobo... you can connect up to 3 fans with this one but i just modded my cabling to accommodate two fans...
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February 8, 2011 11:34:34 AM

sure, I understand not wanting to overload the MB. But two 0.11A fans will draw less current than one 0.40 amp fan. There are plenty of those, and that would be fine to attach to a header rated 1A, so why not two that have half the current draw? Is there something specific about there being TWO fans, or is it just an assumption that two will be too much current? If the latter, that seems very shortsighted, considering the vast range of power needed by modern fans
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a b à CPUs
a b K Overclocking
February 8, 2011 12:18:08 PM

Its only about the initial power draw than anything else... as i said earlier i have previously hooked two fans onto one header with no problems but ensured those fans less amp to start...

the noctua fans are specified for 1.32W input power, 110mA current and 12V Voltage and your mobo's cpu fan header delivers maximum 1 amp/12 v for the fans... so technically if you are running two fans whose initial power needs are half of 1amp then it should be OK...

Quoting gene - the splitter config i specified earlier does exactly that... send only one rpm signal but receives pwm for all fans (if they are pwm fans)... noctua doesnt supply pwm fans so its OK...
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a b à CPUs
a b K Overclocking
February 8, 2011 3:57:52 PM

Part of the reason you are hearing that advice from people in forums like this is because we tend to be overclockers. The less stress on the mainboard's power system, the better it overclocks.

Also, there was a time when fan headers were designed to power only one fan.

If you're not concerned about getting a super-duper overclock then go ahead and do multiple fans.
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