So I writing this because I googled stir plates for homebrew and found a bunch of stuff that says “it’s easy, just….blah, blah, blahâ€. I tried to build a stir plate and just got pissed because it didn’t work the first time and I wanted to brew the next day and I had other stuff to get ready. {Ok, I wasn’t an English major and my sentences run on, at least I spell check} I got it to work, but it sucked and it still does. I vowed to get back to this at some time.
Then I saw this post and found that I wasn’t the only idiot that having a bitch of time (p.s. apologize to everyone that I threw into the idiot bucket with me).
I know that BYO had an article on how to build a stir plate and probably covers all this, but I wasn’t a subscriber at the time so I don’t have that article. I do have some yeast in the fridge and I’m f***ing impatient, so I decided to reinvent the wheel and here it is.
1) E-bay, look for magnetic stirrers not stir plates, you’ll get more results. I searched for stir plates and everything came up at $100 or more.
Did I mention that I’m impatient? I want between 4 & 6 stir plates. Why? Because I binge brew 2-3 ten gallon batches per weekend a few times per year. Why? Because I trash the garage, basement and the laundry room when I brew and one clean up is better than 2-3. So, I didn’t want to skulk around E-bay hoping to find enough working stir plates at a reasonable price to fit my bill. You get the point. Back to item 1, if you want one stir plate, e-bay may be the route to go, just do the right search.
2) Build your own using a computer fan and some sort of voltage control.
Note: I’m not an electrical dude so let me know where I’m wrong here.
From this thread I found that there are three ways of controlling the voltage
A) Potentiometer
This was my first attempt. I wasn’t sure what to get so I got the 25 ohm and the 5000 ohm potentiometers (pots) from Radio Shack (two best choices from not many choices). 25 ohms is not enough to get the voltage range with the fan and the power supply that I was using (12V power supply, 60mm computer fan). The 5000 ohm pot was too much. The speed control with this setup sucks. Radio shack doesn’t have a great selection so I was stuck with this.
What I found: If you want to go the pot route with a 12v power supply, 100-200 ohms is more the range that you want to be in. At a 100 ohms (with the fan that I’m using) you can get a reasonable range of speeds for 2 Liter flask and a 2†magnet. If you fill a 1L flask about half full (500 ml for the SBB), then you can go up to 200 ohms and still spin the liquid. As a final note, you probably want to a pot that can handle at least 1 watt of power to keep it from burning up.
The final thing to consider with a pot is how many turns it takes to get the full range of resistance. A single turn 100 ohm pot will go for 0-100 ohms in slightly less than one turn. A ten turn 100 ohm pot will change by about 10 ohms per turn, which gives finer control. The ten turn pots are more expensive.
What I recommend. Purchase a 50 ohm and a 100 ohm 5 watt single turn pot (linear not log) and put them in series. Fair amount of control, reasonable price, simple to build. For the deluxe version, add an on/off switch and a push button switch to temporarily bypass the pots to get the fan started. Parts can be ordered from
www.digikey.com, part numbers for the pots are CT2153-ND and CT2154-ND. Warning, shipping and handling sucks for small orders. The other option would be to purchase 4 to 8 of the 25 ohm pots from radio shack and string them together.
B) Build the LM317T circuit posted by Test Engineer. What I found: The circuit works well but certainly takes time to put together and get to work (unless you do this sort of stuff a lot). My main problem with this circuit was getting right balance between fixed resistor 1 and the variable resistor (pot). I’ve figured it all out and I have diagrams, charts, graphs, etc, PM me if you want help in building one of these.
C) The 555 timer circuit. In theory it works by pulsing the fan at 12 volts. The pot adjusts the ratio of the on/off time for the voltage. I would attach a picture, but I’m a ‘tard and I don’t know how to post pictures. What I found: It’s a confusing circuit to build for amateurs like me. If you don’t do it right, it would hard to trouble shoot. Same goes for it breaking, hard to trouble shoot. And finally, it didn’t work well. It pretty much was on or off, same as the 5K pot, just harder to build.
So, for what I’m doing, I plan on going with option number A x 6. Why, freaking simple compared to the rest of the stuff.
BTW, the magnets from hard-drives can screw up your stir bar if you’re not careful. Just ask me how I know. You can also fix the stir bar with the same magnets.
It works right now, but soon will be g 
<see, it's getting better.
