Building a Stir Plate for Brewing
Using a stir plate can help a yeast starter grow faster and healthier quicker. Brewing 10 gallons batches can get expensive so I have looked at all kinds of different ways to cut down on ingredients cost. Using a stir plate along with a yeast starter allows you to purchase one packet of yeast for a standard 10 gallon ale recipes or high gravity brews or even lagers.
Everything in this do it yourself can be purchased at RadioShack or taken from old electronics around the house. This is a great project to show your wife that the old PC in your closet, shes been trying to throw away for years, was there for a reason. The stir plate I built was taken from a bunch of different source online so I am not really sure who to credit, regardless here is a stir plate that can be used for brewing that is very cheap, easy to build, quiet and will save you money.
Gather Necessary Equipment
1. Project enclosure box($7 at RS)
2. 4 inch 12 volt DC PC fan (pull out of old PC or buy one online)
3. Rare Earth Magnets (pull off of old hard drive from old PC or buy at RS)
4. Power Supply 12V to 6V DC (old cell phone charger/keyboard/Nintendo or buy one at RS)
5. Power Switch ($3 at RS)
6. Rheostat/potentiometer 25 Ohm, 3 Watt ($3 at RS)
7. Washer/Screws/Bolts ($2 at Lowes)
8. Strong Glue or Epoxy
9. Rubber Feet (pull off of old PC or buy at RS)
10. Stir bar, 1-2 inch (order online $6-$8)
Listed below is the equipment I used to build the stir plate.
Attaching the Magnets
Use a large washer when attaching the magnets to the fan. This gives the magnets something to hold on it and prevents too much interference on the fan motor. I used both rare earth magnets out of one hard drive, one magnet was not enough. If using two magnets stack them on top of each other, I could not get it to work with them separated. To remove the magnets from the hard drive mount plate, simply wedge a flat head between them and tap it with a hammer. Center the washer on the fan and use gorilla glue or epoxy to attach it. I did not glue my magnets down, but it wouldn’t hurt to do so.
Testing the Fan with Magnets
Rather then just jumping in and soldering, I figured it would be a good idea to simply cable it all up and test it out. To do this I used temporary wires with alligator clips to connect the power supply, power switch, potentiometer and fan. Make sure the power supply is ALWAYS disconnected while working on the circuit, electronics can be very dangerous so be careful. Remove the connector on the end of the fan and power supply then strip the wires. The positive line out of the power supply should go directly to the supply contact on the switch, different switches have different contact layout. The ground wire form the power supply should go to the fans ground wire, which is usually black. Next connect the load contact on the power switch to the center pin of the potentiometer. Lastly connect the positive line out of the fan to the right most pin on the potentiometer. Here is a wire diagram of how the circuit should be connected.
While testing make sure that the fan is supported by a clamp or something. Do not hold the container with the stir bar above the fan, this will not work. The container will need to sit on on the clamp, approximately 1/2 inch from the magnet. Also make sure you are using a jar/flask/container with a flat bottom, if it is concave/convex it will not work.
Mounting the Fan with Magnets
Alright so the fan/magnets work and the stir bar spins, now lets package everything up so that it looks nice. First you need to mount the fan to the top of the enclosure box. To do this clamp the fan to the top of the enclosure and marked the holes to the exact location and drill bit size.
Mount the fan using 10-32 x 2 screws and bolts.
Wiring up the Switches
Drill a small hold in the back of the enclosure box and run the power supply cable through it. Pull it with enough slack to work with then tie it off, so that it cannot be pulled out. Drill holes in the front of the enclosure to seat the power switch and potentiometer. Soldered the positive line from the power supply to the power switch.
Next solder the middle pin of the potentiometer to the load contact on the power switch, I used the white wire here.
Wiring up the Fan
The fan has two wires, positive(usually red) and ground(usually black). Solder the positive line out from the fan to the right most pin on the potentiometer. Then attach the ground wire out of the fan to the ground wire from the power supply using a standard wire connector.
Attach the new enclosure top with the fan to the enclosure box using the provided screws. Flip the enclosure over and attach rubber feet, they will really help with vibration.
Flip the enclosure back over, plug it in and place the flask with the stir bar in the center, the magnets should line up. Place the potentiometer on the lowest setting and power it on. Gradually increase the speed to create more stir.
Here is a video of it in action.
That’s it, go brew more beer! If you have any comments or questions please post them below.