Is it possible to turn a 20in fan into a small wind turbine?
The fan blades will make a very small turbine. The motor probably won’t be much use. You need a motor with permanent magnets to act as a generator. Shaded pole induction motors on fans are not much use. You could think of the drive motor from a video recorder, possibly a valid size. The link below shows a few small wind generators, including one with a VCR motor, and the Chispito is another simple design well worth looking at, that seems popular. The VTR motor has a three phase alternator, so the output is rectified to get DC to charge the battery. Read all those and search for more, so you will get some ideas of what to do. Wind generators need plenty of wind, and may need permits, especially beyond a certain size. The power you can get from a back yard model is not much, so don’t expect that. A small unit like you suggest is a good learning exercise. It will be more like 50W than 200W. It is unlikely you can store and return more than a couple of hundred watts from a 12V battery exce
