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Old 09-22-2012, 08:12 PM   #1
Chaddyb
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Default STC-1000 In fermentation chamber constantly going from heat to cool

So, I just got my STC-1000 wired up in my old chest freezer. Everything works as it should, it kicks the heat on, and the freezer on when it should. Ive been wathching it all day today as ive ben working out in the garage, the air temp in the garage is roughly 60 degrees. I have the controller set at 68 degrees, and the probe in a gallon jug of water. The unit always keeps the chamber within 67.5-68.5 degrees, so thats good I guess. The problem is, It will kick the heat mode on to bring it up, which it does, then the temp will creep up above the set range, and kick the coolong on, which brings the temp back down, but then it will creep down below the threshold and kicks the heat back on. This cycle seems to continue endlessly. It takes about an hour to swing the temp from one end to the other.

My question is, is this fairly normal? I have a ceramic heater for heat, and im wondering if its heating the air too quick, and getting it too hot? Its a 750 w unit with a fan. I might try to turn the fan off so it heats things less rapid too.

Also the chamber can fit 6 carboys in it, so its rather large.

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Old 09-22-2012, 09:29 PM   #2
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I've had the same problem. What I found works best is to use the smallest heat source you can. The small ceramic reptile heaters work great. I also leave a fan running inside at all times. This won't stop the overshooting on the cooling cycle but it will help the heating cycle.

Also I use a lamp dimmer on my heat source which is actually a 150w enclosure heater for an electronics enclosure. I work as one of the head support guys for those tvs that you see across the country on gas pumps and we use those to keep the systems warm when the outside temps drop too low. It's basically a heat sink with a heat coil built in that has a fan mounted on top. If I use that thing at full power, I'll overshoot my heat temp every time. So I have it cranked down to almost nothing and that seems to work the best.
At least my temp stays more stable that way and my freezer cycles a lot less.

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Old 09-23-2012, 03:13 AM   #3
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I think I will have to try a different heat source, this one seems to overshoot it every time. I have heard the reptile heaters work good, I'm thinking about building a paint can heater as another option.

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Old 09-23-2012, 03:21 AM   #4
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A gallon jug for the probe to sit in is a huge amount of thermal mass, which could also be contributing to the overshoots. Do you have anything in there besides that right now? It's generally not a good idea to run empty.

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Old 09-23-2012, 01:26 PM   #5
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Quote:
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A gallon jug for the probe to sit in is a huge amount of thermal mass, which could also be contributing to the overshoots. Do you have anything in there besides that right now? It's generally not a good idea to run empty.
No its empty other than the jug o water. I had the sensor hanging in mid air, and the fluctuation was much more rapid that way, the water takes it a lot longer.

The only reason I'm running it empty is to see how everything acts, and to try to fine tune things. Maybe I will fill a fermenter with water and try it out.
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Old 09-23-2012, 06:09 PM   #6
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That controller doesn't have as many options as one would like to see, but by increasing your differential, you should be able to minimize the constant switching you are seeing. What do you currently have it set at? If it is really low (1 or 0 degrees), your system will continuously run trying to stay at exactly the setpoint.

The rapid cycling will really decrease the lifetime of your compressor.

I'd recommend setting the differential (how far the temperature can swing from the setpoint) to 2 or 3 degrees and put the temperature probe in a gallon or half gallon of water. That temperature will swing faster than your beer assuming you have more than a gallon of it.

Also, you may disconnect the side that you don't need. If it is colder outside the chamber than you want it (or warmer), unplug the compressor (or heater). The ambient temperature will slowly change the interior temperature to its trigger point, where it will turn on the cooler or heater to bring it back to the target.

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Old 09-23-2012, 06:17 PM   #7
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I had the best control running with two full carboys, whether or not they were both full of wort. The added thermal mass really slows things down. I started with a 150W ceramic reptile heater but that was just way too big. I then found a 60W one and that one was better. Anymore, I just use the one that is going to be most likely needed. I really only need heat when the ambient temperature is below the fermentation temperature, otherwise I leave it unplugged during the remainder of the year.

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Old 09-23-2012, 09:10 PM   #8
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Quote:
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The only reason I'm running it empty is to see how everything acts, and to try to fine tune things. Maybe I will fill a fermenter with water and try it out.
It will behave completely differently with 5-15 gal of liquid in there. Freezers aren't designed to be run empty, and freezer manuals usually have strongly worded warnings advising against it. Not only are you not getting an accurate picture of how it behaves, you're also needlessly cycling the compressor and reducing it's life expectancy. You can prevent the temp overshoots without changing the temp differential by changing the probe placement (once you get some thermal mass in there). Since it sounds like this is a ferm chamber, I'd suggest taping the probe to the side of the fermenter of the most recently brewer beer, and then taping something over it to insulate against the ambient air a little (folded paper towel, piece of foam, rag, etc). This will give you very accurate temp control, eliminate your overshoot issue, but still give enough thermal mass close to the probe that opening the lid won't cause immediate changes. If you really want a permanent location for the temp probe, I'd suggest using a much smaller container of water, like a yeast vial, or 8oz water bottle.
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Old 09-24-2012, 12:36 PM   #9
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The best place for the probe is taped to the side of a carboy with insulation like a sponge (or inside it) giving you a direct temperature measurement of the wort temperature. The wort will heat/cool much slower than a baby food jar full of water and will reduce the freezer compressor cycling.

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Old 09-24-2012, 09:51 PM   #10
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Cool, thanks for the suggestions, I will try to throw a couple fermenters in there and move the placement of the probe. Then I can see how this thing reacts. Thanks again.

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