I'm thinking about building a 3d printer ventilation system, with three 3 pins current computer fans, controlled by an Arduino Uno. Is it possible to run 5 volts on each fan, or do I need a stronger Arduino?
If you want to control computer fans with an Arduino, then it's sooo much easier to get 4-pin fans.
3-pn fans need extra transistors and other parts. 4-pin fans have that already build-in.
You can find 4-pin fans on CPU coolers.
You still need a 12volt supply to power them.
The Arduino is a controller, not a power supply.