If you’ve ever used a magnetic stirrer before, you know how handy they can be. I’ve made several on this general pattern, and use them in the garage for mixing paints and dyes, and in the kitchen for making cold-brewed coffee. This design is common in the homebrewing community, where it’s used for stirring yeast cultures to make homemade starter.
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Steps
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Step #1: Gather materials
- The acrylic case I used is an AMAC 772C 2-part box with lid. They are available at The Container Store for a couple of bucks. It measures 4x4x2" with the lid in place.
- 12V 80mm fans like this are common in computer equipment; the one I used was recovered from a burned-out AT power supply.
- The DC power jack is a size N, coaxial, panel-mount component. (Radio Shack #274-1583)
- You will need at least two, and preferably four, small neodymium supermagnets. Mine were 6mm discs, 3mm thick, that I got by breaking open some cheap plastic fridge magnets.
- The mounting hardware consists of four 1.5" 6/32 flat-head machine screws, eight matching hex nuts, four matching flat washers, and four matching split washers. I splurged and got stainless steel, but regular zinc-plated steel should work just as well.
Conclusion
Computer fans are generally rated for 12V, but will run at lower speeds with lower voltages, so you can control how fast your stirrer turns by controlling the driving voltage. Experiment to find a battery or DC power supply that provides a convenient speed for your purpose, or connect the stirplate to a variable voltage regulator. A battery pack, power switch, and/or voltage regulator could easily be built into the case to provide a portable unit.
