Pwm issue on crosshair iv formula z

[ross_a_mcivor]

Hi can anyone help, I'm just a beginner in electronics, but not in pc building, the issue is when I connect fans to any fan socket, if I just use one fan, it spins up and down and is controlled, if I just use the sence and pwm wire and join it to a bank of fans (send just to one of them), and power them by a12v Molex they spin to 50%, or about 7v, rpm is being reported but the pwm doesn't control them, is there any way of giving the fan header the indication that there's a fan there and start controlling them all, please help.

[jab383]

You are right to use a molex power connection because multiple fans can overload the power limit of a motherboard header. That applies to the 12v and ground connections. It is also right to connect the sense wire on only one fan so the motherboard BIOS and OS software can monitor fan speed without interference from more fans on that sense wire.

The trick is to connect the pwm wire to all the fans. They all need the control pulses. Most splitter cables work that way. I have two places where I split a PWM signal 5 ways by this method:
Molex power and ground to all fans, pwm wire from the header to all fans and one sense wire from one fan back to the header.

hope this helps.

Jeff

[ross_a_mcivor]

Thanks I assumed that u put it better than me, just in that setup the fans still run at 50%, if I don't put anything on the 12v and ground the pwm sticks to a pulse of 50%. If i just connect one of the fans to the power from the motherboard, they all behave. Maybe a resister cross the 12v and the ground to fool it, but i ain't attempted this before and I'm not really sure I'm right 🙂