Bought fan splitter, now fans are too loud.

kuski · Aug 21, 2017

So I bought this new case which is Fractal design define C. The case came with 2 extra fans ( 1 in front and 1 in back ). Because I had 1 case fan from my old case which is noctua fan, I decided to put it in the rear of the new case as exhaust and put the 2 fractal fans in the front as intake. When the build was done I realized I can only connect 1 case fan to my motherboard so I connected the noctua fan to it and ordered fan splitter cable. Well the cable came and I plugged it into the motherboard and then connected it to the fans ( btw the fractal fans had only like 3 pin connectors and the noctua has 4 pin) and then plugged the cable into one of the psu cables, cause it takes the power from the psu. Well then I powered my pc on, while I still had my side panel off to see if the fans spin and yes all of the fans spin, but there is 1 problem. The noctua fan in the rear for some reason spins too fast, probably at 100% and is very loud all the time. I tried quickly to change the speed with speedfan but couldnt get it to change the fanspeed. ( I looked some tutorial online but dont know why it didnt work ). the cable is Flexa FP55 from akasa.

My PC specs: cpu: i5-4460
motherboard: gigabyte B85M-DS3H-A
ram: 2 x 4gb ddr3 1600 mhz, kingston hyper x
gpu: asus dual gtx 1060 6gb

raisonjohn · Aug 21, 2017

The problem is your Gigabyte B85M-DS3H-A motherboard's 4-pin SYS_FAN header -- it's not a true PWM (despite having 4 pins). Only your CPU_FAN is PWM (i.e., provides constant +12V at Pin #2 and provides Speed Control/PWM at Pin #4). On the other hand, the SYS_FAN header on your motherboard provides variable voltage/Speed Control at Pin #2.

The Akasa Flexa FP5S would require a true PWM header for it work as intended. Notice that in the splitter, the 4-pin connection to the motherboard only has 2 wires (Pin #3 and Pin #4) on it. Those 2 pins are the Sense (or tachometer reading) and the PWM/Speed Control, respectively. What the splitter does is use the constant +12V power from your PSU (via SATA) and use the PWM signal coming from Pin #4 of the motherboard's header to vary the speed of 4-pin PWM fans. The Pin #3 just gives the reading of how fast the fan (that is connected to one of the five splitter that has a Sense wire) is spinning.

Unfortunately, since your SYS_FAN header cannot provide PWM signal/Speed Control on Pin #4, the result is, only constant +12V is supplied to your Noctua 4-pin fan (via the SATA power). Thus, such constant voltage will make your fans run at full speed 24/7 (akin to plugging it on the PSU directly).

kuski · Aug 21, 2017

Oh. Thanks for the informative answer. Do you think it would work if I connected the fan splitter to my cpu_fan and the cpu fan to the sys_fan in the motherboard?

raisonjohn · Aug 21, 2017

kuski :

It's not recommended.

The CPU cooler is a PWM fan that is highly recommended to be plugged into the CPU_FAN header (which is a true PWM header). Plugging such CPU cooler on a non-PWM SYS_FAN header may make your cooler run in full speed if +12V is constantly supplied to it. You may be able to change some BIOS settings for such header to lower/vary the voltage supplied to it but it is not recommended for PWM fans (which are intended to work on full +12V power with a PWM signal).

But more importantly, if your CPU cooler is plugged in another header other than the CPU_FAN, your motherboard might not detect if such CPU cooler fails - putting your CPU at risk (though your system may also just safely shut down to protect your components).

My Suggestion
If I was in your position, I would suggest to hook it up this way (though others may also have their own way of doing it):

I would group the two PWM fans you have (i.e., the Noctua rear exhaust and the CPU cooler fan) and install them on a PWM header (i.e., the CPU_FAN header) via a PWM splitter (i.e., the Akasa Flexa FP5S you already have).

I would also group the two DC fans you have (i.e., the two Fractal Design pre-installed case fans) and install them on a non-PWM header (i.e., the SYS_FAN header) via a 2-way 3-pin splitter (which you need to buy for about $5, such as this: https://www.amazon.com/Splitter-Extension-Sleeving-Connectors-Length/dp/B00C46DX4S).

So,

CPU Cooler Fan ---> Akasa Flexa FP5S (plug this to the one which has a 4-wire connector labelled "Master")
Noctua PWM Fan ---> Akasa Flexa FP5S (plug this to any of the remaining four connectors with 3 wires)
Akasa Flexa FP5S ---> CPU_FAN header and SATA power cable

Fractal Design case fan #1 ---> 3-pin Splitter
Fractal Design case fan #2 ---> 3-pin Splitter
3-pin Splitter ---> SYS_FAN header

kuski · Aug 21, 2017

So I took your advice and tried to do what you told and it was going all good until the last point where I had to connect the 3 pin splitter to the sys_fan, cause it cant go there, since they both are ''male?'' connectors. So what I did? Well I improvised, I did everything you said, but then I connected 1 of the fractal fans to the sys_fan header and other fractal fan to the akasa splitter. It actually worked :O, all fans spinning. Still kinda loud though, well then I tried speedfan and boom I was able to control my noctua fan. All I have to say is big thank you to you sir. I would not had figured this out without you. Now im off to do the cable management!

. thx

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Bought fan splitter, now fans are too loud.

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