PWM fans on Y cable with 3 pins & 4 pins?!

danw25

Distinguished
Nov 12, 2010
28
0
18,530
Hi, got a coolermaster seidon 240v , it comes with two PWM fans. it also comes with a Y cable that connects to the mother board with a 4-pin connector.

this is the interesting part : the two male ends of the Y cable are different, one has 4 pins the other 3.
how can both fans have PWM enabled if only one fan is connected via 4 pins?
thanks!
 
Solution
It depends on which pin is missing from the 3-pin connector. If it's the 3rd pin then the fan still runs in PWM mode but doesn't rely it's RPM back to the system. But if the 4th pin is missing then yes, that fan can't run in PWM mode since 4th pin is used for PWM control.
It depends on which pin is missing from the 3-pin connector. If it's the 3rd pin then the fan still runs in PWM mode but doesn't rely it's RPM back to the system. But if the 4th pin is missing then yes, that fan can't run in PWM mode since 4th pin is used for PWM control.
 
  • Like
Reactions: bullipatty
Solution
What you got I'm sure is the proper design that will work just fine. To control a fan the mobo header does NOT need, nor does it use, the speed of the fan. Fan speed is used for only two purposes: info and amusement value to YOU the user, and monitoring for fan failure if the speed signal stops. Neither is involved in fan control.

Any fan header can deal with a speed signal coming in from only ONE fan. The signal, carried on Pin #3, is a series of two pulses per revolution. If two or more such pulse series are presented to the counting circuits on the header with the unpredictable and changing differences between them, the speed measurement counter gets terribly confused and give wildly changing values. So any proper Splitter or Hub will send back to its header the speed signal of only ONE or its fans and ignore all the others. That is why only one of the two output arms of your splitter has a pin at position #3. When using such a device, since the mobo cannot measure the speed of ALL the fans, you are responsible from time to time to check that all your fans are working and there are no failed units.