Do you have old desktop PCs/computers laying around your house and it gets super hot where you live? Well, you don’t have to buy a USB fan, you can make one from those ol’ PC fans.
You probably also have some old USB wires laying around. Just cut them off, wire them to the PC fan (refer here for USB pinout) using pin 1 (5V) and pin 4 (GND), voila!
You have a working PC fan. Of course, if you want to get more technical, you can probably add a voltage regulator to top-off the voltage at 12V. I have also done testing where I overclock PC fans up to 24 volts no problem. Most PC fans are made well enough to handle voltage spikes and you can easily power them up to about 20 volts np.
Hey, you know what, I will make one of these soon, then you can see how well they work as fans!
You can see how I overclocked my PC fans when I was making hoverboards here.