My Projects Technology

Using a Motherboard RGB Header to Power a Tiny 12v fan

Why would one do such a thing? It’s going to take a few posts to flesh out this situation but I wanted to share something interesting. If you have a need to power a tiny 12v fan, like this one I ordered from Amazon you can draw power from your motherboards JRGB header/s (if you’re not using them for lighting). I’m using an MSI B450M Mortar motherboard and was thinking of a way to power the small fan:

Is the fan diminutive or do I have remarkably large fingers?
Connected to the header on the motherboard and working well.

Now before having fun with this sort of thing you would be well advised to check your user manual to check what voltages you’re dealing with etc. and which way the pins are oriented. This seems to be a pretty common configuration for JRGB headers but YMMV. Here’s the an excerpt from my manual:

Reading this you can see pin 1 is labelled and now we know the orientation.

As you can see pin 1 is +12v and pin 2 is G (for green). Easy to adapt to new headers on the cables if this needed to change but since I’m not using the JRGB headers on the motherboard at all I just kept the header that came with the fan.

To activate/test the fan remember you’re using the JRGB header so you need to tell it to light up the colour the pins are connected to, in my case green. A nice touch is the brightness you specify for the colour corresponds to the relative speed of the fan (meaning if you tell it to be 50% bright the fan will spin at 50% speed).

So what am I doing with a 3cm (30mm) fan in a standard mATX case? Basically the same reason I had to sound-proof my cabinet – using enterprise equipment in a home environment. This time sound wasn’t the issue as the 10GBe PCIe network card I’m dealing with has no moving parts. The interface would continually shut itself down reporting overheating, and it’s no wonder – I’m using a small mATX case and the card is crammed against the power supply. Also my 120mm case fans weren’t helping, although pretty with their RGB lighting they were only pushing around 30CFM of air each. I just upgraded to 2x Corsair ML140 Pro fans for the front which can push a cool 97CFM each at full speed, however due to noise (I know) I’m running them at 50% (top fan) and 75% (bottom fan) speeds.

Airflow is good in general now but the small fan was just to guarantee there was air passing over the entire heatsink of the network interface, and let me tell you I’m not proud of my install work but it certainly works:

That lone cable tie is the hardest working component in the system. /s

Ideally the fan would be installed to blow over the heatsink but alas there is no room, and a more inclined and involved person could likely 3D print a shroud to fit the fan nicely, funnel the air from the front of the case appropriately or, you know, use a bigger case.

Finally my fan only draws 0.07a @ 12v, 0.84w. I don’t know how many amps these headers can safely supply being designed for LED lighting so you would be ill-advised to power anything more demanding.

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