PC Fan Magnetic Stir Plate

thingiverse

I utilize this versatile stir plate to create yeast starters with 2L flasks, making it an essential tool in my brewing process. Although I've had it on my list for the past three or four years, I'll finally document its use, but don't expect a comprehensive guide just yet. Be aware that the cap and base dimensions may not match perfectly, so ensure the top of the cap's magnets reaches the surface of the base. If you print the cap and it sticks up too far, simply reprint with a smaller design. The fan size parameter allows for some scaling in the design, but the 2x fan mount screw holes remain fixed, requiring you to input that value separately. I've only tested this setup with an 80mm fan, which produces a top diameter of approximately 125mm, roughly matching the size of the flat part of a 2L flask. To create a solid surface on the base, set `magnet_cover` to a positive value (usually one layer is sufficient). The cap may also need customization to accommodate your specific fan hub dimensions, blade count, and magnet sizes. I use two 3/8" round magnets that are 1/8" thick and positioned at the top of the cap's holes. Both a 25mm and 30mm stir bar work well in this setup, although you can adjust it to suit your needs. For control, I employ a 2.1mm barrel jack input for 12V power and an LM317 circuit with a potentiometer and single resistor to regulate the output voltage. You can find the circuit design by searching online. Additionally, I run two stir plates in parallel using a splitter from a single 12V 1A power supply.