Home Brew – DIY Stir-plate

Inspired by one of my friends, I’ve decided to get into the world of home-brew beer. Of course I looked over all his gear and immediately got obsessed with the electronic components and how I could somehow automate things and connect things to the web… raspberry pi’s etc etc… but I did notice something much less ambitious, a magnetic stir plate, which is used for making the yeast starter in the home brew process.

Here is the finished product:

Components I used:

  1. Cigar Box – Had one around.
  2. AC-DC 12V Adapter (1.0A) – $10
  3. DC female input – $1
  4. Illuminated switch DC – $1.50
  5. Future Kit 804PWM based DC motor controller – $10
  6. Nice knob to attach to the potentiometer on the PWM controller – $1
  7. Standard DC Fan 80x80mm. 12V, 2.4W. Range 7-15V – $7
  8. Hard drive magnet – $4
  9. Stir bar(s) – $5 each
  10. General bits (wire, things to elevate the fan position)

Few things I learnt along the way:

  1. Don’t JUST use a potentiometer, use PWM. A common approach is to simply use a potentiometer between the power source and the fan. The main reason this is not effective is that standard DC fans need a rather ‘high’ minimum voltage to even rotate, in the case of mine, 7V. What this means is practice is that the majority of the potentiometer turn does nothing (I used 500 ohm, the smallest I could find), and that 7V was too fast to effectively bring the stirbar into a controlled spin. The better approach is to use PWM, in very simple terms this always provides full voltage, in this case 12V, but pulses it on and off very quickly to control the speed. What this means is that rotation of the potentiometer on the PWM controller gives you full control of fan speed. I was lazy and bought a pre-made PWM controller, if you’re more adventurous you could assemble a kit or built from schematics found all over the web, for example.
  2. Careful removing the hard drive magnet. I broke mine, fortunately it still works ok. Suggest you be very gentle and follow the instructions in this video.
  3. 2mm thick neodymium magnets are not enough. After I broke my hard drive magnetic I bought two 2mm thick circular magnetics, these were not strong enough in my case, would suggest around 4mm. I ended up using my broken hard drive magnets.
  4. Have the right tools. In my embarrassingly many attempts to build this I did so without the right tools, which caused lots of frustration and shorted components. The tools I ended up buying made the entire stir-plate DIY more expensive than buying a generic one… but lessons aren’t free 🙂 and thats no fun. Some ‘tools’ I’d recommend are:
    • Stand/Holster for your soldering iron
    • Something to hold PCBs, wires etc to free your hands. For example.
    • Multimeter (mine one’s battery was flat the first attempt)
    • Test using a 9V battery rather than full 12V 1A DC source
    • Not a tool, but if you’re unexperienced like me… watch some YouTube videos about how to solder!

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