PWM on my mobo help

[ajhoranny89]

Hi guys i have the Asus crosshair v formula z am3+ and it has pwm fan headers. i noticed that it says chassi-fan1,2,3 and opt-fan1,2,3 next to the headers. I have the h440 case with 3 fans on front 2 on top and 1 as outtake, some fans are connected to the header sayin chasi-fan and some other connected to the opt-fans Headers. Sometime when i turn on my pc the the outtake fan dont turn on but it is kinda shaking a lil bit and i touch it, it fills like its stock but it shakes the same goes for some of the front fans. So i just wanna know how this pwm work so i can set these fans however i please to, and still have them automatilly on their own Any video or comment are welcomed ty guys. All the fans work propeely cuz this set directly and they are super loud.

[FatalityDiablo]

whaaat I'd love to help, but I don't understand. just plug everything to pwm and it will be fine?

[ELSknutson]

man thats hard to decipher 

[ajhoranny89]

Lol sorry ill repost this again i was just typin fast cuz im at work and doin it on my phone

[dfsdfgfkjsefoiqzemnd]

PWM fans get 12V all the time. The PWM itself (Pulse Width Modulation) simply turns them on and off several times per second. the length of the "on" and "off" periods determines the RPM.

 

Maybe this explains it better :

Image stolen from homepower.com

 

 

 

If your fan doesn't want to turn, either the pulses aren't long enough for it to actually start spinning, it doesn't get enough voltage or the fan motor itself is borked. 

Seeing as you already verified that they do work when plugged directly to a 12V source, it's safe to assume that it isn't the last of these options.  So either the motherboard's fan headers don't supply sufficient voltage or the pulses are too short to overcome the magnetic force inside the fan motor. 

 

The fan headers on a motherboard can power one or two fans, but the circuits are too thin to provide enough power for multiple fans at the same time.  I gather from your first post that you only have one fan in each fan header, so that theory can also be dismissed.

 

I suspect that the fan profile simply needs to be tweaked.   The base percentage is set too low, which means that the pulses are too short to keep the fans spinning (or to put it in car terms : the idle is so low that the engine stalls).  

Raise the minimum RPM or percentage the fans get by any substantial amount and see if that helps.  If it does, lower it again until you find how far down you can safely take it. 

[ajhoranny89]

PWM fans get 12V all the time. The PWM itself (Pulse Width Modulation) simply turns them on and off several times per second. the length of the "on" and "off" periods determines the RPM.

 

Maybe this explains it better :

Image stolen from homepower.com

 

 

 

If your fan doesn't want to turn, either the pulses aren't long enough for it to actually start spinning, it doesn't get enough voltage or the fan motor itself is borked. 

Seeing as you already verified that they do work when plugged directly to a 12V source, it's safe to assume that it isn't the last of these options.  So either the motherboard's fan headers don't supply sufficient voltage or the pulses are too short to overcome the magnetic force inside the fan motor. 

 

The fan headers on a motherboard can power one or two fans, but the circuits are too thin to provide enough power for multiple fans at the same time.  I gather from your first post that you only have one fan in each fan header, so that theory can also be dismissed.

 

I suspect that the fan profile simply needs to be tweaked.   The base percentage is set too low, which means that the pulses are too short to keep the fans spinning (or to put it in car terms : the idle is so low that the engine stalls).  

Raise the minimum RPM or percentage the fans get by any substantial amount and see if that helps.  If it does, lower it again until you find how far down you can safely take it. 

So it doesnt matter what header i connect the fans to? cuz there some headers that on pcb says opt_fan and other that says cha_fan. I should still get the pwm workin on every fan regarless where theyre connecte?

[dfsdfgfkjsefoiqzemnd]

opt = optional

cha = chassis

 

Not sure how your motherboard handles those.  Maybe only the chassis fans are controlled based on the temperature, maybe all of them respond to the temperature or CPU load, maybe something else. 

 

Currently looking at the user manual for your motherboard  Fan setup starts at page112.  Will edit this post if I find something useful there.

 

 

 

 

EDIT : right ...

 

Chassis fans : Fully customizeable once you turn on their control.  Minimum RPM can be set from "ignore" to 600 RPM in 100RPM increments. 

You can choose between standard, silent, turbo and manual profile, the latter being one you can modify yourself. 

Should you choose the manual profile, you can set up temperature limits (low as well as high) and fan percentages at those. 

So if you're struggling with a fan that's connected to a cha_fan header, you can sort it out by increasing the minimum RPM and maybe the fan percentage at the lower temperature limit.  Fan speeds can be set from 40 to 100% in 10% increments.

 

As for the optional fans, the manual isn't exactly clear.  If I interpret it right, even if you enable fan control they won't turn on until the CPU reaches the minimum temperature you selected (25, 30, 35 or 40°C).  they'll then ramp up until they max out when the CPU reaches the temperature you selected as maximum (60, 70, 80 or 90°C)

 

 

 

 

Conclusion : check the menus to make sure the fan controls are active and set up properly according to the temperatures that your CPU does with your cooler and usage pattern.