This is fan assembly iteration 2. The first iteration can be seen in a prior post. I have been working on this assembly for months, trying to find a 120 mm fan that works (literally), is powerful enough to blow air through a HEPA filter, and has a connection for a power outlet. Most 120 mm fans have connections for computer interiors and require adapters for direct connection to power outlets. After ordering a few fans, I was finally able to connect a high speed pressure fan directly to an outlet using a 12V DC power supply with 4 pin Molex.
The assembly looks under-engineered mostly because it is. At the start, I designed a 3D printed model that required 3 days of printing. My printer is close to my desk and I simply can not tolerate the printer running for longer than 30 hours straight. I changed the design to accommodate aluminum sheeting as a shaft. Interior parts were hot glued in place. Jewelry pins were used to seal the door hinges. Iteration 3 should have a more polished look to it. Well,,,at least I hope it does.
As I was putting the assembly in the enclosure, I realized it made more sense to pull the air from the enclosure rather than pushing it through the filters. I turned it around and put the fan on the outside. The video below shows the fan working. I learned right away that suction does not work unless the door is closed. It will possibly work better when the back fan is covered. That fan is used to control the temperature in the enclosure. I turn it on when air coming through the fan assembly feels too warm on the back of my hand.
I found the fan I used for testing, Nanoxia Hydra High Speed Pressure Fan, to be too loud. The fan I used for the first iteration is the same as the back fan, AC Infinity. It’s sound level is 18 dBA whereas the sound level for the Nanoxia Hydra fan is 58.7 dBA. I wanted a powerful fan to push air through the HEPA filter, but since I have learned to do otherwise, it is no longer necessary. I have returned to using the AC Infinity fan for now. Hanging string moves toward the assembly; however, not as strongly as shown in the video. I must find a different fan.
If you want to use iteration 2 as a basis for your own fan assembly or improve it, here is a link to the Tinkercad file.