PWM fan mod problem

[DigitalONE]

Hello
i bought a 1.74 amp delta fan and my motherboard supports 1 amp only, so i removed the red and black wires and connected it to the molex and the yellow and blue wires to the motherboard's system fan header, the fan works and i can see the fan's speed but can't control it's speed, neither through bios or fan control software, i thought the fan is bad, so i tried another pwm fan that is less than 1 amp using the same method and it did the same thing, so i connected that fan directly to the motherboard and pwm worked fine, if i disconnect the red and black wires from the fan header pwm doesn't work, anyone knows why this is happening?my mb is H81M-S2PV rev. 1.0

[Helpful Tech Witch]

It might be that since it’s not conected to the board and drawing power, the bios is confused and just both thinks it’s there and on and not at the same tine

[WoodenMarker]

Is the fan header set to use pwm? Is the fan running at max rpm with just the first two pins connected? 

[svmlegacy]

If the fan is not connected to the motherboard, there's no way for the system to communicate or see it.

[thrasher_565]

this is is the mod

 

Edited September 14, 2021 by thrasher_565

[DigitalONE]

thanks for your replies

i found out the cause of this issue, it's the motherboard's system header, pin 2 is responsible for +12v and speed control, i can't use that pin because of the fan's high amperage, that's why i can't control the fan, but on the cpu header pin 4 is speed control, i didn't expect that the headers are different, i've added an image from the manual

 

[For Science!]

1 hour ago, DigitalONE said:

thanks for your replies

i found out the cause of this issue, it's the motherboard's system header, pin 2 is responsible for +12v and speed control, i can't use that pin because of the fan's high amperage, that's why i can't control the fan, but on the cpu header pin 4 is speed control, i didn't expect that the headers are different, i've added an image from the manual

 

What exact fans are you using? Speed control on the Pin 2 is via DC control, not PWM.

[thrasher_565]

13 hours ago, DigitalONE said:

thanks for your replies

i found out the cause of this issue, it's the motherboard's system header, pin 2 is responsible for +12v and speed control, i can't use that pin because of the fan's high amperage, that's why i can't control the fan, but on the cpu header pin 4 is speed control, i didn't expect that the headers are different, i've added an image from the manual

 

might be able to change it in the bios but ya probably just use the cpu header