Somehow this project is never ending for me. Just 4 years ago I made a third version of it and it helped a lot, even though it was ugly inside and not powerful at all, but I didn’t think of making a new one because it was enough. But just the other day I was disassembling an old server and inside it there was two powerful centrifugal fans (12V 1.85A, ~25W) and thought I make an upgrade with one of these…

And this time I also wanted to have a metal pipe, not PVC. The fan is 12V, so a larger battery is needed, I made it using a spot-welder after assembling all the parts I needed.
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