PC Fan Magnetic Stir Plate

I use this stir plate to do my yeast starters with 2L flasks. This is not really a work in progress but after having it sit on my TODO list to post this for the past three or four years so I guess I'll never get around to making this a proper howto or build guide. The cap and base dimensions may not match each other! The top of the cap / magnets should just reach the top surface of the base. If you print and the cap sticks up too far, just print a smaller cap.

The design should somewhat scale with the fan_size parameter, but the 2x fan mount screw holes are in a fixed place so you'll have to enter that value as well. I've only tested with an 80mm fan which makes a ~125mm diameter top, roughly the size of the flat part of a 2L flask. The top surface of the base can be made solid by setting magnet_cover to a positive value (usually one layer is good).

The cap will probably also need to be customized to suit your fan hub dimensions, blade count, and magnet sizes. I use 2x 3/8" round magnets that are 1/8" thick and pushed to the top of the cap's holes. Both a 25mm and 30mm stir bar work fine, although it can be tuned to work with whatever size you need.

For control I use a 2.1mm barrel jack input for 12V, and an LM317 + potentiometer + single resistor to set the output voltage. Google around for the circuit. I also run two stir plates with a splitter off a single 12V 1A power supply.