Building a Stir-Plate
To brew a beer that has a high ABV, it helps to have more yeast and a starter is very useful for generating more yeast before pitching into the wort on brew-day. Although it is not required to make a good starter, a stir-plate can help grow even more yeast. Here’s a Stir Plate I’ve been working on to help make yeast starters for brewing beer.
The two main DIY Stir Plate designs that I have come across are:
- LM317 Adjustable Voltage Regulator w/ DC computer fan.
- Rheostat controller w/ DC computer fan.
For my design I thought I’d try things a bit differently by using an AVR mictrocontroller (Attiny13) and a 4-Pin PWM computer fan. I don’t know that there is any real advantage to my design over the others, but since I was able to get a 4-pin PWM fan for the same price as a regular fan, I figured I would use the built in PWM to control the fan speed.
- Attiny13 Microcontroller
- 4-Pin PWM 12V Computer Fan
- 2 Rare Earth Magnets
- 1″ Stir-Bar
- Radioshack Project Box
- LM7805 Linear Regulator
- 10k Potentiometer w/ Aluminum Dial
- 12V 600mA Wall Adapter
- Lighted On/Off Switch
- Various Resistors, Capacitors, Hardware, etc…
In total everything cost about $40; much cheaper than the $100 stir-plate at the homebrew store!
Building the Box:
The fan I used was just a standard 12V 4-pin PWM computer fan from Amazon. To attach the magnets I first super-glued a metal washer to the back side of the fan to give myself a nice flat surface for mounting the magnets. I had to make sure to get the washer on straight because if it was off by a little bit the fan would wobble around due to the weight imbalance.
After getting the washer on, I then super-glued the magnets on top. Honestly, the super glue probably isn’t even necessary for this because they stick to the washer well enough without glue. I decided to glue them down just in case, spacing them about an inch apart (the same size as the stir-bar).
I did a lot of testing at first before I knew how far to space the magnets, and how far away from the stir-bar they had to be. To get the stir-bar to couple nicely with the magnets, it took a little experimenting.
I used some spacers to keep the fan the right distance from the top of the box to make sure it coupled well with the stir-bar. Here is what everything looked like while mounting the circuit board and the fan in the project box:
All the circuit parts were mounted onto a small perforated board I had laying around. The board is mounted onto the back side of the box, so that the screws are not visible on the top or front of the box.
After everything was soldered on it looked something like this:
Swirling Vortex of Doom!
To make this starter I used 1 cup of DME, and 2 Cups of water. Eventually it will be used to ferment a Belgian tripel, with an OG of 1.090!
After pitching the starter into my Belgian tripel wort the yeast took off like a rocket!