DIY Magnetic Stirrer Progress

A beer brewing friend asked me to build a magnetic stirrer for his yeast cultivation setup.

The stirrer I'm building uses the core of a 80mm brushless DC computer fan with its blades cut off, sanded, balanced, and mounted on a piece of strip board. Some carefully cut and sanded 1" PVC coupling and pipe hold a neodymium magnet rod in place. There is transparent plastic shielding around the motor to prevent wiring from getting caught in it during operation.

The speed control of the motor is realized with an adjustable LM317 linear voltage regulator. This is the circuit I made.

12V Computer Fan Motor Speed Control Circuit

In this circuit the maximum voltage at the fan motor is only about 10V, but that should still be plenty fast for a magnetic stirrer.