Fermentation controller part 1

I brew beer.

I’ve been doing it for the last 2 years, more seriously than I did in College. And I am going about it in an all out sort of way. I ferment in stainless steel conical fermentors, I have
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created temperature controlled heating belts to control temps in winter, so I can get them exact, and I have pursued consistency to a RIDICULOUS extent. As one home brewer pointed out- you can make great beer with a bucket and some parts from the toilet. The problem is getting it perfectly repeatable every time. So I have built an expensive and overly high tech brewng controller, multiple devices for various aspects of brewing. The one thing I have not done, and it is mostly because of size, is to convert a refrigerator or freezer into a fermentation temperature controller so I can brew all year round and be able to make repeatable beers. I live in a 1000 square foot house with a wife, 2 kids and a new puppy. There is NO space for anything. At the moment, I brew beer like a madman all winter and spring long, because once summer hits, I cannot keep the beer cool as it ferments, and as such, I get funky flavors and unrepeatable results.

I thought I was doomed to brew only in winter, until I saw a thread on homebrewtalk.com titled “conical fermentor heater/cooler.” This page showed a link to the manufacturer of my conical fermentor, and had a guy who had just built a cooling unit based on little 9 amp Peltier coolers for computer CPUs. The build was simple, not pretty and not refined, but it looked like a space saving and very effective way to cool a fermentor, without having to purchase a whole refrigerator, which I
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just don’t have room for. And it was cheap.

It became clear immediately that this would become my next big project. I would change the design a bit, but use exactly the same Peltier coolers, and the same general idea, which involves milling 2 pieces of aluminum to precisely fit the outside dimensions of the fermentor, so that I can attach the pelters and transfer as much heat as possible out of the fermentor and into the surrounding air. The original design uses a heating pad in addition to the chillers, and uses an aquarium thermostat which can control both heating and cooling. These controllers are “on-off” types… if the temp is lower than set point, it turns the heater on, and if above the set point it turns the heater off and the chiller on, etc, within a hysteresis band that is generally 1 degree wide. I am forgoing the heating pad, and using a PID controller to keep the temperature within 0.1 degree, and just reversing the polarity on the Peltier’s to provide heating. The big downside to my design is that in order to switch fem heating to cooling, I have to actually manually flip a switch. But, since I already had a PID and a high quality RTD temperature probe, I thought it better to just use this. Besides, I like the tighter control of temperature and I figure that in summer I am not going to have to do any heating, anyway, so most of the time I will just need to sweet it to heat or cool based on the season. OH--- and then after planning on doing it this way to save money, I decided to spend even more to buy a programmable pid that allows me to program a set of temperatures, times, and ramp times. Do I need it… nope. But it gives me a capability that I otherwise wouldn’t have had.

Now, form factor matters to me. I don’t want lots of stray wires all over the place, nor something very ugly to look at, and I do not want something that will be a hassle to set up and use. And I tend to like a little bling in my electronic devices to make them look good. So rather than follow this guys plans, I adapted them so I will have a simpler unit, with detachable heating units that can be unplugged for easy
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storage, and inst
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ead of 4 wires going to each side of the box, I will use a single 4 wire sheathed cable to control everything on the heating elements.

So, I bought the things needed and started going. On a previous project I bought an XY table for my drill press, so I could run it as a badly functional milling machine. This came in very handy for creation of this project, as the internals of the box have lots of grooves and structure that makes it difficult to get things to fit just right. I slowly had to mill away some of the protrusions on the enclosure so all of components would lie flat. I did this VERY slowly, taking no more that about 1/2 mm on each pass to make sure I wasn’t putting too much stress on the machine. It is a cheap (but still highly effective) Skil brand drill press, but even the best drill presses are really not intended to be used as mills. The chuck is held on entirely by friction and could pop off at any minute, flying through the air with a very sharp end mill on it. Yikes. And they are not built at all for lateral forces, which make the chuck even more likely to fly off, and can screw up the bearings. But a mill costs thousands of dollars, and my drill press cost about 129 bucks. So I just took it unbearably slow so I would’t put too much pressure on the bearings. And I said a little prayer before turning on the machine each time.
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I started with an 8x14x4 modular aluminum project box from ebay, planned the layout in illustrator, and then started drilling holes. The second picture above shows the areas that I milled on the inside. Initially I tried to just use my dremel, but it was taking approximately forever, so I abandoned that. Besides, I was doing it handheld and am sure I would have found a way to cut my finger off or something.

My biggest dread was making the holes for the top of the box. I needed to fit 2 components in that , according to my drawings would be an incredibly tight fit. Add to that that each component had only a 1.5mm lip on the outside to hold it in place-- if I made a cut too large by only 1.5mm, the component would just fall through. In previous projects I had just used a jigsaw to make the cuts, but I really didn’t want to screw this up. I marked the thing about as accurately as I could, went at it with a drill and a skill saw, cutting well within my margins. The IN got out the end mill again,as that would allow me to make perfectly straight cuts and trim off less than a mm at a time until I had it perfect. Thus worked very well, but at the end I still got out the hand file to make nice sharp corners, and to make a few bulges in places where the power supply bulged. I got the cutout PERFECT… not even the slightest wiggle. Thank god for my little “milling machine.”
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