Making Stirplate - Yet Another Do-It-Yourself Stir Plate

I have done several batches of beer now, and since I want to try doing a Lager or a Kölsch before winter winds down, I figured I better start making some yeast starters. And hey, another excuse for a frivolous DIY electronics project. Today I put together a stir plate. If you want to make one like this, I have itemized the parts and prices below. You would also need an erlenmeyer flask (we have a 2000 mL flask) and a 25 mm stir bar.

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Desktop Plastic Project Case Box 5.51″ x 4.33″ x 1.38″ $6.90
Thermaltake Mobile Fan II External USB Cooling Fan $10.92
SPST Small Rocker Switch $1.62
USB Extension Cable (2) $7.98
Neodymium Magnets 1/2 x 1/8 inch Disc $5.89

Total cost $33.31I chose the Thermaltake fan because it is 5 volts so I can power it over USB, and it comes with a built in speed control potentiometer with a nice metallic finish knob. I unscrewed the bolts and tossed the cage and stand.

The potentiometer knob is just held on by tension, but it is a lot of tension. I needed some pliers to pull it off.

There is a small clip on the potentiometer that holds it into the bracket. Depressing the clip allowed the potentiometer to be pulled out.

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These mounting nibs are in the way for mounting the fan.

A quick buzz with the cutoff wheel on the rotary tool got them out of the way enough to move forward with mounting the fan.

I marked out the holes and drilled them out with a 1/8 inch bit, then ran the bolts that held the cage on through the box and fan and used the nuts that came with to lock it down.

I am using the female end of one of the USB extensions as a power jack.

Here I lined it up to the back plate to cut out with the rotary tool.

4 wires to a standard USB cable, Green DATA+, White DATA-, Black POWER-, Red POWER+

Test fitting after making the cutout. Meh… good enough.

Next I cut off the female end of the other USB extension cable and striped the wires on both male ends to solder them together to make a power cable for the stir plate.

Twisted up and ready to solder. I also used some electrical shrink wrap to make the connections and cable nice.

I cut out the front plate of the project box with the rotary tool to make a place for the rocker switch.

Had to take out one of the bolts because the switch wouldn’t fit. Three should be enough, right? Now to wire up the power.

I was going to use these handy clips, but my crimping tool is the wrong size and I just ended up butchering the whole pack of clips.

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Oh well, more soldering.

Now to find a good place to position the potentiometer knob.

1 / 4 inch drill bit seems to be the right size.

Fit is good enough.

Hot glued the USB female power jack and the potentiometer to the case.

Next I centered and hot glued the magnets to the fan. The magnets are stacked 2 high.

It spins!

A test run before adding the box cover gets a good lock on the stir bar and creates the expected vortex.

Unfortunately, with the cover on, I can’t get a lock on the stir bar and it flies off almost immediately. I tried adding another magnet to each stack, but it presses against the top of the box and wont spin. Either way, going to have to do some more cutting.