Air Purifier (active carbon filter) for 80mm fan

thingiverse

I've decided to get better air quality in my home. In cases where there are cats, dogs, smokers, or poor air circulation, an air filter is always a good idea. I've bought a bunch of active carbon sheet filters (2 pieces) for my solder fume extractor and 3D printer enclosure air filter. The active carbon filters are 13x13cm, so they should be powered by a 120mm fan, like the ones I used in my previous projects. Unfortunately, 120mm fans aren't very common, so I decided to design something for an 80mm fan, which are easy to find. I didn't want to print a big and ugly adapter cone, so I came up with the idea of keeping the same filtering surface (130x130mm) but splitting it into four 75x75mm surfaces, creating a "cubic" filter. This filter is compact and nice, you can simply place it on one side or "vertical" using its feet. To power the fan, I used a reclaimed wall charger, 7.8V 1A, which is perfect for the job. The fan is a standard 12V PC fan, but it can reasonably work down to 5V. Less voltage means less air flow, but also less noise, I think that 8-9V are the sweet spot to reduce the fan noise by a lot without sacrificing too much air flow. It depends on the specific fan you're using, but 3-400mA are usually more than enough. Since I planned to have the filter working 16h/day, I chose a power supply that can provide twice as much current, so it doesn't even get warm. I've also added a simple switch, to stop the filter without removing the wall charger. The standard fan has three wires: positive (red), negative (black) and speed control (yellow). Just ignore the yellow wire, connect the negative from the wall charger to the black cable, and put the switch between the positive wire from the wall charger and the red cable. The screws are four M3x40mm (at least 40mm, the hole is actually more than 80mm deep), I've decided to add a small grill for the fan, which I didn't design because there are literally hundreds of them on Thingiverse. This is it, now I have my cheap air purifier!