DIY Stir Plate

A while back I began work on a diy stir plate. The reason being is that 1) I’m cheap and 2) Why not do it myself? Most stir plates that I’ve seen cost $100 or more, and building one myself only costs around $20 (if you don’t screw anything up). I won’t claim that I know very much about electronics engineering, but I think I know enough to be able to accomplish simple projects. And plus, any mistakes that I made along the way clearly add to my knowledge, so it’s win win for me.

The most important part of this, the parts list;
1) Power supply (I used a AC to DC adapter, 12v 1 amp)
2) On off switch
3) Potentiometer/Rheostat
4) Computer fan
5) Case (I used a cigar box)
6) Rare earth magnet(s)

In the end, the build is pretty simple. I spliced the power supply so that I had my positive and negative wires. Connected the positive to the first pole in my switch (my switch has three poles because it also has a built in LED). Then I connected one of the other poles to the negative wire of the power supply (after trial and error I discovered which was which). The other remaining pole I connected to one of the two outer poles of the potentionmeter. After this, I connected the middle pole of the potentionmeter to the positive wire of the computer fan. I made sure that the magnet was glued to the proper side of the fan, and mounted it inside the box. And voila! I have myself a working stir plate.

Now, the mistakes that I made was that I tried two different power supplies, first at 9v and then at 12v. The problem was I didn’t pay attention to the amps that it was capable of outputting. Both of these power supplies worked fine, and provided enough power to get everything going, but there was one simple problem. The vortex was puny, and that’s being nice. Once I used a 12v adapter with proper amperage, everything worked nicely.

Additionally, I didn’t really know how everything was supposed to work. After some research, it was easy to understand that stir plates are really there to keep the yeast in suspension. Of course, this is done by stirring everything with the magnet stir bar. When you test your stir plate, toss some water into your flask and then some pepper to show you the movement generated by the whole setup. Once I did this, and saw everything working, I got a little giddy.

A word about sourcing everything; Everything is available pretty easily at your local electronics store, and nothing should be too difficult to obtain. The rare earth magnets might be the more difficult ones if you want free, because you can get these from a hard drive. They are pretty simple in the end and all it takes is a hex head screw driver (or bit) and an old/obsolete hard drive. Once you have the bracket containing the magnet free (and this should be quite easy to identify, the magnets are strong) you bend the bracket gently and the magnet should come out easily (they are usually held in place by some sort of epoxy/glue).

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