Member Avatar for Zeus@Sagerquist

I just bought the ASUS X99-PRO / USB 3.1 motherboard. I put it into a Corsair 800D case, that has 7 fans. I need to split the fan connectors to handle 2 fans each, and the top 3 fans all together from 1 fan connector. How much power in watts is provided by the fan connectors on the motherboard?
Note: The book explains that the CPU fan connector provides 12 watts at 12 volts, and makes no mention of the power output of the chassis fan connectors.

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Short summary and practical plan: the X99-PRO manual explicitly documents the CPU_FAN header capability and lists the board fan headers, but it does not give a separate per‑CHA_FAN wattage in the same place — so treat each motherboard fan header as limited and verify before you split too many fans off one connector. (manualslib.com)

How to decide before you buy/split: power = 12 V × current. Typical modern 120 mm PWM case fans draw a few hundred milliamps (many high‑quality fans are 0.05–0.2 A, some budget/high‑speed models 0.3–0.4 A), so you can often put several low‑draw fans on a single 1 A (12 W) header — but some fans (industrial/Delta types) can exceed 1 A on spin‑up and will overload a header. Check each fan’s rated current on the sticker/spec sheet and add them up. (microcenter.com)

Splitter behaviour and what to buy: passive Y/splitter cables simply share the header’s power (and usually only present one tachometer/PRM signal back to the board). That means motherboard PWM will usually drive all connected 4‑pin fans to the same duty cycle, but the header’s amp limit still applies. A powered PWM hub (powered from SATA/Molex) is the correct solution if you want many fans to follow motherboard PWM while not drawing current from the header — the hub takes power from the PSU and uses the motherboard’s PWM lead as the control input; most hubs only return one RPM signal to the board. Confirm the hub explicitly supports PWM input and PSU power. (newegg.com)

Concrete steps for your Corsair 800D + X99‑PRO:

  1. inventory each fan’s rated current; 2) check the manual for which headers are available; 3) if the total per‑header would exceed ~0.8–1.0 A, get a SATA/Molex‑powered PWM hub (attach its PWM input to the chassis header you want controlled); 4) set Q‑Fan/Fan Xpert in the BIOS to control that header and verify RPM/behavior. If the Swiftech unit you saw is not PSU‑powered, don’t use it for three heavy fans — use a powered hub instead. (manualslib.com)

(References above are the X99‑PRO manual, sample fan specs and practical splitter/hub descriptions.)

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Member Avatar for Zeus@Sagerquist

The trick is controlling the speed on ALL fans.

If I were to plug a 1=2 splitter onto a case fan connector, (not a CPU fan connector), both fans would run and the computer can control the speed for efficient cooling. But the case fan outlet doesn't provide enough power to run any more than 1 fan.

I've seen a 1=3 splitter, and only 1 fan will get the wire that reports speed, and power is reduced to control the fan speeds.

Now if you use a different power source, other than the motherboard's case fan outlet, you can't control the fan speed. But this model looks like you can. Does it control the speed of ALL fans connected to it based on the setting fed to it from the motherboard fan outlet? IOW all fans get matching speeds?

Member Avatar for rproffitt

As to the trick I linked to a product that seemed to do this. If you claim the motherboard already does this, why the question?

Member Avatar for Zeus@Sagerquist

The motherboard doesn't have 1 socket for each fan and there are 7 of them. And the sockets don't have enough power to split them to run 2 or 3 fans on 1 socket.

So I want to run the power from 1 socket into this gadget you mention to run the 3 top fans and control all three with matching speeds through motherboard settings/controlls. It looks like this thing will do that. And with 8 ports on this unit, there will be 5 open/unused.

At 14 bux, I'll get a second one for the hard drive fans (2 of them) and they'll run at same speeds controlled by the motherboard.

2 other chassis fans will plug into the 2 remaining sockets and I'm set.
Thank you for the post.

Member Avatar for ServeYourSite

For a 4 pin peripheral the red cable will provide 5 and the yellow 12.

Member Avatar for Zeus@Sagerquist

I know that. How many watts at 12 volts? You'll see it's not enough to run any more than 1 fan with the exception of the CPU fan. Asus's book says 12 watts there. But doesn't address the wattage of the other case fan sockets.

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