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Question related to the 3 built in RGB fans

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I'm trying to help my son build a PC. Neither of us really know what we are doing, but so far we've done pretty well following how-to videos (I think). We need some help figuring out how to plug in the built-in fans though.

He's got a Corsair 4000x case and a Aorus B450 Pro motherboard (AM4). I added two extra fans (Corsair LL120), which work just fine. Those fans are plugged into the RGB hub and the fan ports on the motherboard. When we power on the PC though the built-in fans light up, but don't spin. Each built-in fan already comes plugged into the RGB hub, but each fan has another wire splitting from the fan that is not plugged into anything. They are just hanging loose in the back at the moment. Do these ends plug into the motherboard like my extra fans or do they go somewhere else?


The Aorus B450 Pro seems to only have 3 fan ports and my two extra fans are plugged into two, so I only have one left.  If the loose ends on the built-in fans do need to go into the motherboard what do I need to do to get extra fan ports? 

Sorry for such a basic question, but I really would appreciate any help you can provide.  

Thank you!


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Corsair RGB fans all have two wires for the fans two separate functions. The fatter 4 pin connector to the motherboard is a PWM connector.  This is 12v motor power and speed control. The flatter 4 pin connector to the circuit board in back is the 5v RGB power. These two functions are completely independent. 

Speed control - All of those fans will need their PWM connector hooked into a fan controller, either the motherboard or a standalone controller. If you are out of MB fan headers you have a few options. 1) Two way PWM splitter. This a Y cable that connects two fans to one control header. They both run the same speed and report as one fan. 2) PWM hub - this is a powered splitter typically for 4-10 fans. It looks like a little circuit board and uses 1 MB header to control the entire lot. 3) Stand alone fan controller. Something like the Corsair Commander XT. It has 6 PWM ports as well as 6 RGB ports and would replace the little circuit board in back. This also makes the fan speed controllable from CUE vs more limited bios options. 


RGB control - You have what you need for this now, but might need to make an adjustment. The Lighting Node Core is a serial device. Your 4000X fans are 8 LED SP-Elite. The new LL are 16 LED ring fans. In CUE you designate one fan type and the number of fans.  The controller understands 8-8-8-8. It will have trouble with 8-8-8-16-16-16. In order to make this work, you’ll want the LL fans in the first 3(?) positions, then the SP-Elite in 4-5-6. Then in CUE you set it up as “LL x 5”. This will generate 80 LEDs in a 16-16-16-16-16 form — enough to cover the actual 72 LEDs you have. 

Even with the above, the 8 led center hub fans won’t do well with the special LL ring effects. So of all of the options for speed control, there is an additional benefit of using the Commander XT. It has independent RGB headers, unlike the serial lighting node Core. You can connect your LL and SP-Elite in any order and controller can handle it. It will automatically detect LED number and set itself up. 

Edited by c-attack
Usual typos
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