Im installing 2 four pins front case fans on a 1 header

[Simon petrikov]

I’m using this fan splitter but it seems that 1 of the 2 entries is a 3 pin, can I still connect a 4 pin fan on this ?

[RONOTHAN##]

Yeah, that third pin is for reporting the RPM of the fan, which will be reported by first fan. As long as the fans are the same, you shouldn't see any issues (even if they are different, you shouldn't, fan control might just be a little weird).

[Simon petrikov]

1 minute ago, RONOTHAN## said:

Yeah, that third pin is for reporting the RPM of the fan, which will be reported by first fan. As long as the fans are the same, you shouldn't see any issues (even if they are different, you shouldn't, fan control might just be a little weird).

Ohh good, they are the same, no panic uncluded

[mariushm]

Each fan sends two very brief pulses of electricity with each full rotation of the fan. So for example, if a fan rotates at 1000 rpm, then it sends 2000 pulses within a second, or one pulse every half of a millisecond. The motherboard counts the pulses and that's how it knows the rpm of the fans.

 

If the signal from both fans gets mixed together into a single wire, then the pulses from both fan may be transmitted at the same time, or just a few micro seconds after the pulses of the other fan, so you don't get an accurate count of pulses, for example the motherboard may count 3000 pulses within a second, or 3500 pulses, and it would show you the fan as spinning at 1500-1750 rpm (divide 3000-3500 by 2) which is incorrect.

 

So the manufacturer of  the adapter cable removes that 3rd pin (the rpm wire) from one fan, to prevent this issue from happening.