Stir Plate Construction

Mad Zymurgists Stir Plate Project
By Jon Koerber & Tom Warren of the Mad Zymurgists Club

This project will teach you to build your very own professional stir plate, for use with up to a 3000ml erlenmeyer flask and standard magnetic stir sticks, from readily available parts.

Sure you could buy one of these at your local brew shop or scientific equipment vendor, but heck, its a lot more fun and satisfying to build one yourself and at around $50, will cost you less than half what a typical professional model will cost you in the store. I also like the fact that our model has a larger work surface and is completely spill proof (a'la NEMA case).

This is a fairly easy project that just about any hobbyist can build in their spare time.  Don't worry, you don't have to be an electrical engineer to build this (I sure am not), we will walk you through everything from buying the parts to assembling and testing your stir plate.

The project should take approximately 3 hours to complete if you have all the parts and tools needed.

PREPARATION
Here are the tools and parts you will need:

Tools

  • Philips screwdriver
  • Needle nose pliers
  • Wire cutters
  • Soldering iron and solder
  • Small crescent wrench
  • Epoxy
  • Drill (drill press even better)
  • Hand saw (table saw even better)
  • Sander or hand sander
Parts and diagrams
You can download and print a complete PDF format parts list here.
You can download a wiring schematic and hole drilling diagram here.

Additional Parts

  • Thin double sided tape (carpet tape)
  • Alligator clips and wire for testing
  • Crimp-on quick connectors for wires
  • Stick-on rubber feet for base

Layout your parts
All the parts you need can be found in this bill of materials document.  We have included part numbers and prices (when possible) for all of the parts we used in the project.  We also included descriptions/specifications for the parts so that if some parts are no longer available from the sources we list, you can search for similar parts from other vendors.  You can see a picture of most of out parts in Figures 1 & 2 below.

PROJECT STEPS
You will find it helpful to view the images provided at the end of this document to get a good overall idea of the project before you begin and during construction.

STEP 1 - Cut your magnet spacer board and mount magnet (Figures 3 - 6)
The first step is to cut yourself a spacer board that will be used to space the magnet higher on your fan.  You want to cut the square spacer from 1/4" plywood.  Make the width of the spacer the exact width of the fan's hub diameter.

Once you have cut the board, draw diagonal guidelines across one side of the board from the corners to help you align the magnet. The goal is to have the stir bar perfectly aligned along the diagonal of the spacer board once the magnet is attached. You can use thin double-sided tape (not the thick padded kind) to test your alignment before glueing down permanently with epoxy. Note in Figure 5 how the stir bar perfectly aligns along the diagonal.

Attach spacer board to the hub of the fan with double sided tape.

STEP 2 - Cut your project mounting board (Figures 7 - 10)
Measure the inside dimensions of your project box to assure a good fit. Using the project box from Digikey, we cut a 6" x 5" board from the 1/8" hardiboard. Sand the corners slightly to round them so they will fit in the project box. Do several test fits to ensure a snug fit.

As seen in Figure 8, mark and then drill the four mounting holes that will secure the mounting board to the project box. Test install the mounting board with the screws to assure an exact fit.

Next you will mark and drill the holes on the mounting board for the bolts that will hold the fan assembly. Carefully measure the mouting holes on your fan. On our fan, the holes were 4 1/8" apart. We centered the fan holes on the project board and then drilled our holes. Test mount your fan on the board by installing the four 8-32 round-head machine screws from the bottom of the board and securing them with four of the nuts, as seen in Figures 9 & 10. Slide the fan onto the bolts making sure the bolts easily pass through both mounting holes on each side of the fan. If you dont have a good fit, cut a new mounting board and start again - it is critical that this fit is precise for the whole thing to come together.

Install the other four nuts onto the bolts. These will be used as spacers to hold up the fan.

Remove the mounting board from the project box for the next few steps.

STEP 3 - Drill holes in project box (Figures 11 & 12)
For this step, refer to the measurements provided on the hole drilling diagram

Align your project box so that the rear and front are the sides do not have the screw holes for the mounting board (side may also have plastic divider slots). You want the panel mount power adapter hole and switch/speed control holes to be diagonally across from each other on the opposite sides of the project box when you are finished.

Carefully use an auger or hole punch to create starter holes for the brad-point drill bits.

Using your drill press or hand drill with a brad-tipped drill bit, carefully drill the hole for the power adapter on one of the sides, and the holes for the power switch and speed control dial on the opposite side of the project box.

STEP 4 - Wiring the power jack (Figures 13 - 15)
For this step, refer to the wiring schematic

Install the panel mount power jack into the case on the side with the single 1/2" hole. Thread retaining nut into place and snug by hand.

In our version, we soldered a 14" piece of our black wire to one of the outside connectors of the panel mount power jack. We then attached the end of this wire and the end of the black wire from the fan using a crimp-on connector that is sized to fit the barbs on the power switch (although you can simply twist them together if you dont have a connector).

Next, solder a 10" piece of our red wire to the other outside terminal of the panel mount power jack (Firgure 15). On our version, we also used another quick connector on the end of the red wire (this will be connected later to the power switch).

At this point you can cut off the yellow wire (if one exists) from your fan leaving just the red and black wires. The yellow wire is not needed for the project and is often used for computers to monitor fan speed.

STEP 5 - Installing the power switch and speed control knob (Figure 16)
Install the speed control knob into the case in the center hole you drilled. If you did not drill the tiny pilot hole for the speed control knob's alignment prong, just make sure that all the terminals are facing up in the project box.

Prior to installing the power switch, we carefully bent the top two prongs (the ones both on the same side of the plastic divider on the switch) at 90° angles since the prongs on the power switch are too long and bump into the fan case. Take a look at Figure 20 below for a close-up of the power switch. The bottom terminal should be clear underneath the fan and should not be bent. If you are uncertain, dry fit the fan onto the mounting bolts after installing the switch with the terminals un-bent and look at the results before you make your bends. Bend the prong so that there is enough room to attach the quick connectors or room to solder the wires.

When you install the power switch with bent prongs, you will need to finagle the prongs into the tight hole you drilled. Don't worry, it should fit. Use a file if you need to give yourseld a few more millimeters of space on the top and bottom of the hole to make the switch fit through - but be careful not to make the hole too large!

STEP 6 - Testing the wiring and operation before final construction (Figure 17 - 19)
For this step, refer to the wiring schematic

It is always a good idea to test your project before you go too far in the construction. There is nothing more frustrating that putting everything together to find out your fan is toast, or you wired the circuit wrong.

For the test, leave the fan outside the project box to give yourself plenty of working room. Grab a homebrew and prepared to celebrate your imminent success.

Using alligator clips and spare wire (not the wire for the project) we will check the operation of the entire project. Don't solder anything in place until you are sure it all works. Don't attach your power adapter until the end of the steps. If you are a whiz with schematics, follow along using the schematics document.

  1. Create a junction between the leftmost terminal of the speed control knob and the middle prong of the power switch
  2. Attach the black wire from the fan to the center terminal of the speed control knob
  3. Attach the black wire from the panel mount power adapter to the top (front, closest to front of case) terminal of the power switch
  4. Connect the red wire from the panel mount power adapter to the bottom prong of the power switch
Testing your stir plate
Now we are ready for a test. Make sure your power switch is in the "off" position (on ours, the led light is at the top of the switch and is off when the switch is rocked in on the lower half.

Turn the speed control knob allthe way to the right (may speed).

Attach your power adapter to the back of the project case.

Hit the power switch. If the fan starts spinning like crazy, congratulations! If not, review the prior wiring steps and make sure you have everything as it should be. If you are still having problems, refer to the troubleshooting section at the end of this document.

STEP 6 - Testing the wiring and operation before final construction (Figures 17 - 19)
For this step, refer to the wiring schematic

It is always a good idea to test your project before you go too far in the construction. There is nothing more frustrating that putting everything together to find out your fan is toast, or you wired the circuit wrong.

For the test, leave the fan outside the project box to give yourself plenty of working room. Grab a homebrew and prepared to celebrate your imminent success.

Using alligator clips and spare wire (not the wire for the project) we will check the operation of the entire project. Don't solder anything in place until you are sure it all works. Don't attach your power adapter until the end of the steps. If you are a whiz with schematics, follow along using the schematics document.

  1. Create a junction between the leftmost terminal of the speed control knob and the middle prong of the power switch
  2. Attach the black wire from the fan to the center terminal of the speed control knob
  3. Attach the black wire from the panel mount power adapter (also has black wire from the fan) to the top (front, closest to front of case) terminal of the power switch
  4. Connect the red wire from the panel mount power adapter to the bottom prong of the power switch
Testing your stir plate
Now we are ready for a test. Make sure your power switch is in the "off" position (on ours, the led light is at the top of the switch and is off when the switch is rocked in on the lower half.

Turn the speed control knob allthe way to the right (max speed).

Attach your power adapter to the back of the project case.

Hit the power switch. If the fan starts spinning like crazy, congratulations! Adjust the speed control knob to make sure your fan varies speed accordingly.

If nothing happens when you turn on your switch, review the prior wiring steps and make sure you have everything as it should be. If you are still having problems, refer to the troubleshooting section at the end of this document.

STEP 7 - Final wiring and construction of your stir plate (Figures 20 - 25)
For this step, refer to the wiring schematic

Now that we know everything is working, we are ready for final assembly.

First off, install your mounting board to inside the case and make sure you have the fan mounting bolts in-place and tightened. Install the second set of four nuts onto the bolts about 1/4" off the platform to act as "stops" for the fan so it is raised up off the mounting board.

Next, in the following order:

  1. Connect the red wire from the panel mount power adapter to the bottom prong of the power switch. Position the wire so that it goes across the mounting board underneath the fan area. If you did not use a crimp-on connector, solder this wire in place.
  2. Carefully install the fan onto the mounting bolts. Position the fan so that its wire leads come out the back on the side of the case where the panel mount power adapter is installed.
  3. Position the red wire from the fan around the right side perimiter of the box. Solder the red wire from the fan onto the middle terminal of the speed control knob.
  4. Attach the black wire from the panel mount power adapter (also has black wire from fan) to the top (front, closest to front of case) terminal of the power switch. If you didnt use a crimp-on connector, solder the two black wires to the power switch terminal. You may want to loop this wire around the right side of the case and then under the power switch and back over to connect it so there is not too much slack wire.
  5. Finally, cut a 3 1/2" piece of our red wire to make the junction between the power switch middle prong and the leftmost terminal of the speed control knob. We soldered one end to the speed control knob terminal and used a crimp-on connector for the end going to the switch.

Perform another quick test of the stir plate now that everything is wired and ready for completion.

Carefully stow the wires so that they will not foul the fan or interfere in any way with it spinning.

You can now attach your selected decorative thumb knob to the speed control pot and close up the box for your final test.

Stick on some rubber feet on the bottom for slip free performance.

Conclusions
Grab a flask filled with water and your favorite stir bar and fire it up! Figures 26 - 29 show our stir plate in action!

We sure hope you enjoyed building our project as much as we did design it. If you liked it, drop us a note on the message board forums.

  -- Jon Koerber and Tom Warren

Troubleshooting tips
Things just ain't working out for you? Well here are a few tips we came up to help you troubleshoot where the problem may be in the project:

[troubleshooting tips to be added later]