How to Build a Magnetic Stir Plate

Building a magnetic stir plate[1] is a great weekend project for beginners. This article shows you how to wire a stirrer correctly when using a potentiometer.

Dan, from emphasizes the importance of wiring a potentiometer with a voltage regulator, he advises against designs that use just a potentiometer to control speed. At low speeds, the potentiometer drops the full voltage from the power supply, since most potentiometers are designed to only dissipate 1/4 to 1/2 watt; the potentiometer requires a voltage regulator to prevent damaged.[2].


  1. 1
    Mount the magnet to the PC Fan by gluing the washer to the top of the fan. Then place the magnet on top of the washer. The washer acts as an electromagnetic shield between the magnetic components of the fan and the mounted magnet.
  2. 2
    Mount the fan to the enclosure. You want the magnet to be as close as possible to the top of the enclosure. Some people use bolts with nuts and washers to raise the fan from the bottom of the enclose.
    • NOTE: Keep in mind that the weight of the container of liquid may cause the top of the enclosure to sink.
  3. 3
    Mount the remaining components (DC power jack, potentiometer, on/off switch) to the enclosure.
  4. 4
    Start the basic wiring by adding the positive and negative wiring to the DC power jack. Then connect the positive line from your jack to the on/off switch.
  5. 5
    Voltage Regulator Pin Diagram
    Wire the Potentiometer, LM317T Voltage Regulator, Resistor, and Fan together.
    Review the "LM317T Flowchart" and "Wiring Comments" images, and the LM317T Voltage Regulator Datasheet[3] link for specific wiring guidelines.
  6. 6
    Wire the Capacitors if necessary. The 0.1 µF capacitor is required if the distance between the DC power jack is greater than 6" from potentiometer. The 1.0 µF capacitor is not necessary but is recommended to reduce transient response.
  7. 7
    Double Check & Turn it on. Double check your connections and make sure wires are not touching inappropriately. Turn your potentiometer about halfway, plug in your 9V or 12V power supply and click the on/off switch if necessary. If it doesn't work, review the diagrams and try to determine what's wrong.
  8. 8
    Add electrical tape to exposed wires. Remove any pieces of wire, solder, or woodchips that may still be in the enclosure. And, tape any loose wires down as necessary.
  9. 9
    FINAL THOUGHTS. This wikiHow uses the flowchart from StirStarters which uses a 330 ohm resistor. I have no idea if it matters that I used a stronger resistor. I was unable to find a LM317 voltage regulator and a 2K Potentiometer so a LM317T and a 5K Pot was used. The Images do not use the 1.0 µF Capacitor because of the added build cost.


  • You can use a multimeter to test problems with your wiring.
  • Do not glue the magnet to the washer. This will allow you to adjust the position of the magnet for best placement.
  • When wiring, add the capacitors last, it is much easier for beginners to understand the electronic schematic/diagram without them, and you can test the stir plate wiring without the capacitors.
  • You can get a PC fan from an old computer or pc power supply.
  • You can get 2 rare earth magnets from an old hard drive.


  • Electricity kills, regardless of voltage. Do not work on electronics while plugged into the power source.

Things You'll Need

  • Enclosure
  • Wire
  • Glue Gun
  • Electrical Tape
  • Computer Fan
  • 1.5" Washer
  • Rare Earth Magnet
  • 5K Potentiometer and some type of knob
  • LM317T Voltage Regulator
  • 330 Ohm Resistor
  • 1" magnetic stir bar (Recommended)
  • Pyrex Erlenmeyer Flask (Recommended)
  • 0.1 µF Capacitor (Recommended)
  • Soldering Iron (Recommended)
  • 1.0 µF Capacitor (Optional)
  • DC Power Jack (Optional)

Article Info

Categories: Hobbies and Crafts