Living in Eastern Europe, I'm experiencing a quite strong heat wave, as some parts of the country got "code red warning", the third time it's happened in recent (documented) centuries. This meas air temperature will rise above 35* Celsius, while buildings and roads (asphalt) may go as high as 72*C, which is simply unbearable.
My room is luckily in the shade of a huge tree most of the day, but the temperature still rises to 27-30*C inside. To combat heat, I'm only using two 30W fans, which can be set up to pull air from the coolest side of the house in different times of the day. They reduce inside temps by a couple of degrees, but at least fresh air is coming in constantly.
On my desk I have a 12 Volt 8cm PC fan, which is connected to a 5V USB power bank, reducing its speed, so it can blow in my direction, without making me sick. For the wiring I used the plug from an old broken USB cable, cut it open and soldered on the fan's wires. Red to the +5V and black to the ground pin. For this application, I don't recommend using the outer layer of the plug as ground, because in some devices it may cause complications.
Here's how the back of the connector looks (with my test wires attached):
The 8cm PC fan is rated at 12V 0.14A, which is 1.68W, but on 5V it consumes less than 1W. With a single cell 2200mAh battery pack
it'll spin for about 8 hours, while my enhanced 2-cell 4400mAh battery pack (from the first picture) could power it for up to 20 hours.This DIY project is really easy and cheap to do, but you can get even better results with a laptop cooling pad
, which also connects to a USB port.
All you have to do is orient it the way you want and be aware that more fans mean slightly higher consumption (but still bellow an average USB port's max power, which is 4W). On the other hand these laptop cooling pads are cat proof, as they can't reach the fan blades.