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12V thermal fan controller help

PrivateRyan

Jun 15, 2022
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I purchased a UPS for my server stack that came with an annoyingly loud fan. Long story short, I replaced the fan with a Noctua to keep it quiet. The UPS was delivering 24V to the fan circuit, so I fixed that with a PCB and a resistor for the 12V Noctua. Runs great. Then I realized that the fan is not needed unless the UPS is tripped. All it is doing is creating noise and collecting dust. So I purchased a W1209 12V thermal controller board that I can set to trip at a certain temperature. It was then I realized I was in over my head. The 12V thermal controller board draws almost zero power when it's not tripped as it is only powering the thermal sensor and LCD display. At least, not enough power to register on my DC power supply. When the thermal board is tripped with the Noctua fan connected to it, it draws 0.10A, or 1.203W @ 12.03V. It seems wiring this together would go far beyond a simple PCB with a resistor, and hopefully not beyond what would be financially reasonable and beyond my novice capabilities. Essentially I need to drop from 24V down to 12V with a variable load. Any help or ideas would be greatly appreciated.
 

Harald Kapp

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Then I realized that the fan is not needed unless the UPS is tripped.
Hopefully your UPS trips only rarely, better never...
The issue with the fan siting idle in between is that it may collect dust and there is a possibility that the fan will not start when it is needed (this is also why most if not alll mainboards run the fan initially at full speed after startup to get it running, then slow it down after a fes seconds.). It is imho preferable to let the fan run all the time. The power dissipated by the fan is probably neglectable in comparison to the power dissipation of your server stack.
I fixed that with a PCB and a resistor for the 12V Noctua.
Here's a part where you can improve efficiency a lot: use a switch mode DC/DC converter (this is a 5-pack, available as single, too). This will reduce power dissipation by almost 50 % compared to the resistor you currently use.
 
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