PWM fans not spinning

spluff

spluff

spluff

Soldato
Joined
19 Oct 2002
Posts
2,599
Hi allm

Just setup my PC and I have 2 Noctua NF12 PWM connected to a Y-cable to the PWM1 connector on the motherboard.

The fans spin up briefly at startup then do not move.

Is this OK?

Is this because the system does not think that it is hot enough to enable them yet?

Many thanks
spluff
 
Normally fans will spin at around 30% at the lowest duty cycle so should turn at some speed or other. Not sure about the Noctua though.
 
Its confusing - in the bios you can set all system fans at once:-

1st/2nd/3rd system fan speed control:- Normal, Silent, Manual, Disabled

I have 2 PWM fans (NF-P12 PWM ) connected to sys-fan1 (these fans either run at full speed or not at all depending on what i select)

I have 1 normal fan (NF-P14) connected to sys-fan3 (always runs at full speed)

I have 1 normal fan (NF-P14) connected to sys-fan4 (always runs at full speed)

I am using a gigabyte Z77x-UD3H
 
Maybe there isnt enough juice coming out of the fan header to keep both of the Noctuas rotating? As you are unable to set them to PWM mode which would allow very low RPM by pulsing them with a decent amount of power.
 
Hi again, could you put a picture of the y-splitter up just so we can check it, or some one with the same Noctua NH-U12F cooler confirm you do not need the Akasa AK-CB002 PWM Fan Splitter Cable.
 
The spliters you get with PWM Noctua Fans are 4 pin, i have some myself. You can also see in the product photo that the spliter included is 4pin:

nf_p12_pwm_3.jpg


So I think its something to do with the Fan Header power going to the fans not being enough to power both? You definitely got it plugged into the CPU fan header that closest to the CPU socket at the top of the board? Try plugging them into the sys fan 3 and 4 and see if the same thing happens.
 
Thanks for your replies....

a. the fans are connected to the sys fan headers (2 on the y splitter are PWM fans) the other 2 are individual on voltage.

b. the motherboard is a Gigabyte Z77x-UD3H - I didnt notice voltages for the fans - maybe I am wrong

Hopefully can sort this out :)
 
under HW monitor, in the bios screen (this is going from memory from my motherboard) there is some settings for CPU fan speed, AUTO PWM Voltage. i set it to PWM for mine.

then 2 more boxes appear, one of them is minimum fan voltage, or something along those lines, with some fans when it said 5v the fans would stop spinning after the initial spin up, but would start to turn once things heated up a tad. i wish i had a camera, but after i have finished rendering my work (another 3 - 5 hours) ill take a look and tell you exacally what its like in mine, i wouldnt think it would be a whole world of difference in yours either
 
yeah if i set it to PWM then the 2 PWM fans change speed...

The other 2 voltage sys fans run at full speed... Can these be controlled too?
 
doesnt say anything about voltages - it mentions slope which affects the 2 PWM fans

the 2 140mm fans still run at full speed :/
 
I had something similar to this happen on my P35 motherboard a few years back, it seemed to be related to possibly not having enough power going through the header for both fans via the splitter. That and the motherboard possibly didn't like both fans on the same header with it being PWM.

All the best.
 
thanks nkata - the fans were supplied with those kind of cables....

I was hoping that the motherboard / windows would allow adjust (automatic/manual) of the fan speed
 
Hi, the y-splitter cable does not give you pwm option for 2fans, you need a Akasa AK-CB002 PWM Fan Splitter Cable mentioned in my 1st post.
 
My 2 PWM fans are Y-split to 1 sys-fan connector via the pre-supplied cable below:-

Extensive Cabling Options - The fan’s short 20cm primary cable minimises cable clutter in typical applications while the supplied 30cm extension provides extended reach when necessary. Both cables are fully sleeved and a 4-pin y-cable allows to connect a second NF-P12 fan to the same PWM fan header for automatic control.

I also have 2 140mm fans which are not PWM which are on 2 seperate sys_fan connectors
 
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