Case fans wont spin up

[Barnz]

Mobo: Gigabyte ga 970a ud3p
fans: x2 corsair af120 (3-pin)

So before, i had these fans plugged into the molex adaptor because I had run out of motherboard headers. Recently, I just brought a pwm fan slitter to plug into 'SYS_FAN 1', which is the only pwn fan header (besides the cpu header) on my mobo.
I do also have the voltage step downs on my fans to make then spin less and be quieter
Basically, one i turn the computer on, the fans spin up and then stop spinning. Sometimes the fans jolt randomly, like they are trying to spin but cant.
I have been into the BIOS and made sure 1st system fan control speed is on normal and not disables however, this does nothing.
The only way i can find to get these fans to work is to restart my computer, then they work normally every-time however, the mother header for fan1 is reading rpm values of like 110000, which is clearly wrong. (although after 5 mins this stops happening)
Do i have a faulty pwn header, or is it just that i have 3 pin fans plugged into a 4 pin adaptor, or is it even that i'm using the voltage step-down?

http://imgur.com/SqdEgiV

plz help

 

[Lutfij]

Mind sharing your full system's specs? Have you made sure your motherboard BIOS is up to date? It seems like the board is having trouble recognizing that there is a fan on the header. Speaking of which, mind sharing the PWM fan splitter's link with us?

 

[Barnz]

Mind sharing your full system's specs? Have you made sure your motherboard BIOS is up to date? It seems like the board is having trouble recognizing that there is a fan on the header. Speaking of which, mind sharing the PWM fan splitter's link with us?

The fan slitter I am using is the akasa PWM fan splitter: https://www.amazon.co.uk/Akasa-AK-CBFA04-15-Splitter-Cable-Fans/dp/B005FWXWPS/ref=sr_1_1?ie=UTF8&qid=1486235947&sr=8-1&keywords=akasa+fan+splitter

Motherboard bios is definitely up to date (especially since the last update for the BIOS was released in 2014, before i build my computer): bios link here: http://www.gigabyte.com/products/product-page.aspx?pid=4717#bios

full pc specs:
CPU: AMD fx 6300 @ 4.1ghz
MOBO: Gigabyte ga 970a ud3p - rev 1.0
GPU: radeon rx 480 (I know there is a bottleneck, i am upgrading to an i5 6600k in like 1 month, maybe new mobo will fix this too?)
RAM: crucial ballisitx sport 8gb ddr3 (2x4) 1600mhz

Also note, there has been an interesting development, the fans do spin up on first boot, they just take 1-2 minutes to start spinning. Im guessing that this is due to the way pwm works, and the fact i have a voltage dimmer with 3 pin fans, connected to this PWM, but it would still be great to get an actual answer.
Also the actual fans them self (not the air they are pushing), are running weirdly hot, like the motor is running supper hot compared to before.

 

[Lutfij]

The way PWM fans work is that the motors are fed with a constant supply of power but according to the sense wire, that power is turned off or on thus the pulse. Based on that info you'll notice that PWM fan splitters have a 12v power wiring and then two more wires for sense wire and control

So for a 3 pin fan, the fans are running at full blast. You should be looking at a fan controller or you can connect off the SYS_FAN2 and PWR_FAN

 

[Barnz]

The way PWM fans work is that the motors are fed with a constant supply of power but according to the sense wire, that power is turned off or on thus the pulse. Based on that info you'll notice that PWM fan splitters have a 12v power wiring and then two more wires for sense wire and control

So for a 3 pin fan, the fans are running at full blast. You should be looking at a fan controller or you can connect off the SYS_FAN2 and PWR_FAN

Nice detailed answer dude, I have decided to just use the slitter on the 3 pin headers instead, just brought another one so I can have 4 fans off the two 3-pin headers. Cheers for the halp tho!

 

[Lutfij]

You're welcome+Thank You for awarding my post as the Best Answer. I assume you know the maximum power output from your motherboard's fan header...? It should be a max of 1A. For some odd reason I can't get to Gigabyte's site to look at the manual.

Edit: It's not stated in your manual. Since Gigabyte's board tend to have revisions and with each subsequent revision there are some components(power delivery) that are reduced from the board's topography.