Sunday, December 13, 2009

The flip side of freezer temperature control is revealed through lousy cabling. LOL WUT

The last couple of weeks have largely been consumed by mundane pursuits unrelated to Fork and Hay. I did make some technical progress in certain areas, learned a little more of the obvious, and harvested a portion of a batch. Let's start with the beer.

Kegged: 091103 Por Favor (half batch)

I want to try filtering. Now that I have some 10 gallon batches underway I feel a little less apprehensive about trying things that have an outside chance of creating loss or waste, and I think Por Favor is a good candidate for filtering. This beer has a tendency to have a yeasty overtone that I hope to drop out in the filtering process, and it would benefit from some additional clarity. With that in mind, I racked one of the two carboys from 091103 into a keg, and left the other carboy intact.

I measured the gravity at 1.018, which is somewhat higher than the expected 1.012. Admittedly, it started higher than expected as well (1.058 vs 1.051), but I still expected this recipe using to attenuate more using US-05. I have a feeling that this is temperature related, because when I went to pull the carboy out of the fermentation freezer the ambient temperature reading was 58 F.

It hit me then, in another one of those insights of mine that are stunningly obvious to everyone else, that...

There's no heater in a chest freezer

I didn't start brewing until May of this year. In Alabama, by May overnight low temperatures already exceed the optimum temperature for ale fermentation, so some type of cooling is needed. I was fortunate enough to have a chest freezer that I could appoint to this task, and it has served me well. However, it's now December and the ambient temperature in my garage overnight is down into the forties.

High fermentation is exothermic, and the fermenting carboys generate enough internal heat to keep the beer at several degrees over its immediate surroundings, provided the wort is warm enough to get the yeast started in the first place. In warmer climates like mine it's necessary to provide some cooling to keep things at the right temperature, and my freezer with its Johnson A419 external temperature controller has worked well. Once the most active fermentation ends the wort temperature reaches equilibrium with its environment. Again, if it's warmer outside the freezer than inside, the cooling circuit will make sure the carboy is held at an appropriate temperature.

It's cold outside the freezer now. As long as the wort is generating its own heat, things are fine, but as soon as that active fermentation phase ends the heat inside takes advantage of imperfections in the insulation and temperatures trend down gradually. It's a freezer, not a Thermos, after all. When I went to get the Por Favor carboy out and saw that the inside temperature was 58 F I realized that I am going to have to find a way to warm my fermenting batches for the next few months.

As The DS18B20 Turns

I probably could have made this observation much more quickly if I had ever completed my quest to instrument things in the brewery. I have made some progress toward the solution while once again confirming how useless I am as a solderer. I'm almost to the point of wanting to switch to conductive epoxy instead of continuing to frustrate myself.

At present I have two probes wired in "powered" mode for the DS18B20, with the devices in the stainless steel probe ends I got at One of these probes has about 15 feet of cable and the other one has about 6.

They have headphone plugs, and I can run them into a Y-adapter and use a single headphone jack for the connection. What I can't do is extend the connection using any of the 50' headphone extension cables I bought. This really frustrates me because I simply haven't been able to figure out why it doesn't work. I have verified the pinouts and corrected the crossovers I found in the cables so that they are straight through. The individual lines are stranded, not solid. Using my multimeter, I can see there's a small resistance in the the cable, on the order of 5-20 ohms. Could that be enough to throw off the timing of the signaling circuit that much?

I bought 100' of six conductor solid telephone wire to run a test. I measured its resistance to be 3 ohms over 100'. I created a simple breadboard to stick 2 DS18B20 sensors at the far end of that cable and wired it into the rest of the stuff I have prototyped. Lo and behold, I can read all four thermometers without issue. Lesson learned: don't expect digital circuit quality out of a $4.99 cable. I will need to rethink my connection strategy now that headphone plugs are not as attractive as they once were.

On a related subject, in order to power these new probes I need to supply them with a 5 VDC circuit. The WebControl board I'm using only sources 3.3 VDC on the connector designated for the temperature probe, but its documentation suggests that the +5V output on the adjacent connector (for a humidity sensor) will be capable of driving probes not connected directly to the board. I tried that and it simply didn't work, so I now use a 7805 voltage regulator device to split the input power and provide a separate regulated 5 VDC supply dedicated to the temperature devices.

I think the experimentation may be coming to an end. I plan to swap out the headphone plugs for RJ45 and use CAT-5 cable for the extensions. New probes will be made out of CAT-5.

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