How does PWM splitter work?

[Filingo]

I wanted to buy a PWM splitter and noticed that most of the sellers sell it as splitter to one 4-pins PWM and the others are only 2/3 pins. They mention it can cause issues if you have 2 4-pin PWM together (mostly Chinese sellers on Aliexpress)

 

But then I noticed Noctua provides a dual 4-pin PWM splitter with their PWM fans. So how does it work? Which of the fans will the BIOS be connected too? And can it really cause issue as some sellers say?

 

Thanks

[WhitetailAni]

From what I understand, the power lines and PWM are just split between the fans, and then one of the tachometer lines on the splitter is connected and the others are ignored.

[Filingo]

2 minutes ago, ragnarok0273 said:

From what I understand, the power lines and PWM are just split between the fans, and then one of the tachometer lines on the splitter is connected and the others are ignored.

elephants!

[Stahlmann]

If you split a 4-pin PWM header into female 2 headers there will be one with 4 pins. This is the header that will give the RPM signal to the mobo.

 

The other connector is a 3pin. This one will power the fan and pass on the PWM signal. But the RPM readout will only be from the other fan.

 

So ideally you should use 2 identical fans when splitting the header up, so the RPM readout will be (kind of) applicable to both fans. 

[Filingo]

3 minutes ago, Stahlmann said:

If you split a 4-pin PWM header into female 2 headers there will be one with 4 pins. This is the header that will give the RPM signal to the mobo.

 

The other connector is a 3pin. This one will power the fan and pass on the PWM signal. But the RPM readout will only be from the other fan.

 

So ideally you should use 2 identical fans when splitting the header up, so the RPM readout will be (kind of) applicable to both fans. 

After this reply I went back to Noctua's splitter page to look carefully, and upon inspection, you're correct! I thought at first it's dual 4-pins, but it's one 4-pins, and the other is 3-pins:
 

https://noctua.at/en/na-syc1

[aDoomGuy]

1 PWM header is unable to interpret tachometer signal from two fans. I have Noctua PWM splitters and only one of them is 4 pin. Despite this both fans will be PWM controlled and if they are the same fan model the speed of one fan is around the speed of the other fan. You can even use two different fans but 1 of the fans will not report its speed.

 

You are also asking which fan will report it's rpm, quite simple, the one connected to the 4-pin side.

[Filingo]

Just now, aDoomGuy said:

1 PWM header is unable to interpret tachometer signal from two fans. I have Noctua PWM splitters and only one of them is 4 pin. Despite this both fans will be PWM controlled and if they are the same fan model the speed of one fan is around the speed of the other fan. You can even use two different fans but 1 of the fans will not report its speed.

 

You are also asking which fan will report it's rpm, quite simple, the one connected to the 4-pin side.

Thank you! Yes, I just noticed that it's one 4-pin and one 3-pin and not two 4-pins:

1 minute ago, Filingo said:

After this reply I went back to Noctua's splitter page to look carefully, and upon inspection, you're correct! I thought at first it's dual 4-pins, but it's one 4-pins, and the other is 3-pins:
 

https://noctua.at/en/na-syc1

thanks for the clarification!