Case Fans at Full Speed using 4-way PWM Splitter

Hi friends,

I just bought this product:
to combine and control 3 of these PWM fans:

As per title, the fans run at full speed no matter my bios settings, they sit well over 1400 rpm all the time and fluctuate up to 1500s.
This splitter uses a molex connector to feed power,while the 4-pin pwm connector has actually only two wires (the 4th and the 3rd) which should be PWM control and Sensor respectively.
My motherboard (asus p8z77 v le plus) describes the 4-pin layout like this: (starting from 4th pin) CHA FAN PWM, CHA FAN IN, CHA FAN PWR, GND).
1st and 2nd pins are empty and all the power comes from the molex bypass.
The 4 pwm male cables that connect to the fans' female are not all the same. One of them has 4 pins in order to recieve signal from one of the fans, while the rest 3 are actually 3 pin so they all integrate for sending a single signal and they should run at the same speed obviously based on the pwm control of the mobo.
It simply doesn't work, and honestly i have not understood how the pwm control works since the power comes from the MOLEX. I tried to use a different header but same results.
I also tried using a single fan to the header without the splitter and worked great, so the header and the fans are not an issue.
Any ideas? My pc is literally like a turbo engine sitting right next to me :lol:
3 answers Last reply
More about case fans full speed pwm splitter
  1. It looks like the splitter you bought doesn't actually incorporate any PWM controls. It just accepts full power from the Molex, and ignores the PWM functionality of the fans.

    I think what you need is a splitter or fan hub that not only physically accepts 4-pin PWM fans, but which also utilizes the PWM functionality.

    This looks like it would work:

    The item I linked is a fan hub with a dial and a splitter. You can connect several fans to it using the splitter, and the dial can be used to adjust their speeds. It looks like it can also be connected to the motherboard's 4-pin fan connector to use the PWM speed control from the motherboard, while the actual power comes from the power supply.

    The one I linked is the only one I can find on Newegg that lets you control the speed of the fans via both the motherboard's PWM and via an adjustable knob. So it seems like the most versatile.

    Here is an example of one that only lets you adjust the speed via the motherboard's PWM:

    And here is one that lets you adjust the speed with a knob:

    The last one only has 3 pin fan headers, but you can connect a 4 pin PWM fan to it; the 4th pin will just hang off and not be connected to anything, but that's fine. (You can connect 3-pin fans to 4-in headers and vice-versa.)

    (Notice that the item I just linked has three different models you can select on the single product page. One accepts Molex power, one SATA power, and one Molex power plus some sort of 12V adapter. I guess the 12V adapter is if you're using it outside of a PC and have just a 12V power supply.)

    I think the first item I linked looks like the best - because it can be adjusted in two ways - but I thought I'd link some more just to show you what some of the options look like.
  2. Yes i am aware of hubs etc. I would just like to find out what maybe wrong. The problem is that the description of the product says "this splitter enables the PWM signal input from the mainboard to control up to max. 4 PWM fans.
    I am trying to understand how the PWM control actually works. It is supposed to send a signal after reading the sensor but in this case the power comes from the molex only and i don't see how the fan would reduce speed
  3. Well it seems that Asus has faked the Chassis Fan Headers and they actually control fan speed with voltage. They describe all headers with the same pin layout, either by mistake or by misleading bad advertising practice.
    Page 2-25 shows the pin layout for all headers which is: CHA (+CPU) FAN PWM, CHA FAN IN, CHA FAN PWR, GND
    The splitter, which is actually a hub feeding from psu directly works ONLY when connected to the cpu header.
    It's a shame cause a bought this product based on the official information released by Asus.
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