Making My Own USB Powered Desk Fan for Less Than $20
9I 3D printed the Noctua designed desk fan.
This is meant to let you use a standard 120mm computer fan as a desk fan and was a design that Noctua came up with selling it as a ready to go desk fan but also giving the 3D print files away for free to anyone who wanted to make their own instead.
The USB to fan header adapter was $6 on Amazon (it was actually two for $12) and uses a boost circuit to take 5V 1A (5W) from USB and "boost" it up to 12V 0.4A (4.8W) to power a standard 12V computer fan from a USB port. Since it's just standard USB power I can use a power bank to power it on the go!
It wont blow you away or anything but it's quiet and certainly nice enough to keep your face cool at your desk on a hot day. Because it's only 1.2W it should run all day long even on a small 5,000 mAh power bank like this but note it might not work on all power banks. My fancier 10,000 mAh power bank with 7 segment LED display to show actual charge percentage doesn't work as 1.2W is actually too low of a power draw. The controller in the power bank turns on for a second, then basically goes "naw this is too low of a current draw here so I can't really be trying to charge anything now" and goes back to sleep. This is a known issue with certain power banks as they need a minimum power draw to wake up. Some power banks you may be able to force on but doesn't seem my 10,000 mAh one can. But turns out it does work on my more basic little 5,000 mAh power bank.
Oh, and also I originally tried it with a 1,200 RPM Fractal fan but found it underwhelming to say the least. I ended up using a 1,500 RPM Phanteks RGB fan that I had lying around (I just cut off the RGB cable to keep it clean) and it's certainly better. But I think to be honest if you're going to build one of these use as close to a 2,000 RPM fan as you can if you want the best results. The 1,500 RPM is nice though as again it's very quiet and is definitely adequate at cooling your face when it's only a few feet away at a desk. So I'd say anything between 1,500 RPM and 2,000 RPM would be good. There are also fancier USB to fan header adapters out there some that do have fan speed control on them so keep that in mind. Most will just do voltage control (5v-12v) but some of the more expensive ones I believe can do PWM control. Given the price of these ones I like them because they're simple and even at full speed this is very quiet and I don't think slower speed options are a necessity.
Overall I really love the design. It's small, quiet and does the job it needs to do! If you have a 3D printer and spare 120mm fans lying around this is an awesome use for them!