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My hardware:

  • Gigabyte GA-Z97N

    • 1x4-pin CPU_FAN header : GND, +12V, Sense, Speed Control
    • 1x4-pin SYS_FAN header : GND, Speed Control, Sense, +5V
  • CoolerMaster Nepton 120XL

    • 1x4-pin pump power connector
    • 1x4-pin fan power connector (fan on radiator of pump)

My question:

Which power connector goes where? Is it as straight forward as pump to CPU_FAN and fan to SYS_FAN? or since they're both dedicated to cooling the CPU should they both go (via splitter) on CPU_FAN?

The difference in pinouts has me confused, as does the potential difference in power needed by a pump vs a normal CPU fan. I also have a splitter, if needed. The Nepton manual is no help, as it's all pictoral.

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    I strongly suggest you contact Coolermaster with this question. – Ramhound Aug 8 '15 at 2:54
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I've confirmed that the Gigabyte GA-Z97N manual says what you've written about the CPU and SYS fan headers but I would guess that the SYS fan header information is wrong (it wouldn't be the first time!).

According to Wikipedia's "Computer fan control" page, "...cooling fans used in computers use standardized connectors with two to four pins. The first two pins are always used to deliver power to the fan motor, while the rest can be optional, depending on fan design and type". It further states that the 'Power' (pin 2) pin is "nominally +12 V, though it may be variable depending on fan type and desired fan rotation speed".

I've read elsewhere that a common SYS fan pinout is: "GND, Fan Power, Fan RPM Sense, +5V (no PWM fan-speed control)". I suspect this is what Gigabyte meant to print in their manual (with +12V or +5V in place of "Fan Power").

I'll bet there is continuity (0 ohms) between pin 2 of the CPU fan header and pin 2 of the SYS fan header (+12V). If no +12V continuity, check for continuity between pin 2 of the SYS fan header and a known +5V source such as pin 4 of the 24-pin power supply header. If no continuity from pin 2 of the SYS fan header to either +12V or +5V, it would suggest that the Gigabyte manual might be right after all (doubtful).

I have also found that the CoolerMaster Nepton 120XL is looking for +12V for both the fan and the pump (per ocdrift.com's CoolerMaster Nepton 120XL review). Note: You want PWM control for both the fan and the pump so they aren't running at full speed all the time.

You should be fine using the splitter as the generally accepted rule with fan headers is all headers combined can deliver 1A of current (or 12W at 12V). When running at 100%, the pump uses about 4.8W (0.4A) and the fan pulls about the same amount of current for a total of 0.8A.

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  • CPU_FAN pin 2 has continuity with SYS_FAN pin 2. So that's fine. And they should both go on the CPU header via the splitter, right? – pjz Aug 10 '15 at 19:44
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    Yes, because the CPU fan header has PWM (Pulse Width Modulation) speed control on pin 4 whereas the SYS fan header does not have PWM speed control on pin 4 (constant +5V). – edgerrr Aug 10 '15 at 19:48
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    I should add that the default setting in the BIOS/UEFI-->M.I.T.-->PC Health Status-->CPU Fan Speed Control is "Normal" which is good because this will allow you to use their "System Information Viewer" program to control the PWM on pin 4 of the CPU fan header. The System Information Viewer app alows you to use four built-in 'auto' modes as well as manually setting a pump & fan (will control both at the same time since they are tied together) speed profile based on temperature. – edgerrr Aug 10 '15 at 20:15
  • So I just noticed that the splitter splits into one female with all 4 pins and one with only pins 1, 2, an 4. Presumably the one with all 4 pins goes to the pump and the other to the fan? – pjz Aug 11 '15 at 14:32
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    Pin three is the 'speed (RPM) monitor' pin and I'm not sure if the pump even sends/outputs this signal. Therefore, I would attach the fan to the connector with all four wires since I'm sure the fan outputs this signal. – edgerrr Aug 11 '15 at 16:08

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