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Home Brew Forums > Home Brewing Beer > Equipment/Sanitation > Johnson Controller Question
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Old 05-07-2013, 02:26 AM   #1
guitarmikeb
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Default Johnson Controller Question

I borrowed a Johnson Controller A419 from a friend to try my hand at a lager. I'm using it in a 5cf chest freezer. The wort is in a fermenting bucket with a blowoff tube installed. The temp probe for the controller is in a bottle of water (probe suspended not touching sides of container, and is located directly beside the fermenter). The setpoint is at 54. I go out and look and the temp reading on the controller is reading 45. WTF? The differential is set to 2 degrees, the ASD is set 5 mins. Regardless of how this thing is setup with the jumpers (ie..cut in/cut out) it shouldn't be down to that low of a temp correct? The chest freezer is located on my back porch and is subject to the environmental temp swings. When I started it around 6pm this evening the temp display read 58.

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Old 05-07-2013, 02:39 AM   #2
Arg1129
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You have to factor in the lag in the temp controller and temperature drop. The controller is only a fancy switch that turns off at a certain point, ie 54 degrees. That doesn't mean the freezer coils, that have to be colder than the ambient temp, will instantly lose all thermal difference and stay at 54. They are still well below that and will carry the internal temp lower. That is why a lot of people use the duel temp controls. When the freezer overshoots, like it always does, the heater warms it back up and the dance between the two persists until there is a balance reached.

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Old 05-07-2013, 02:44 AM   #3
Amff
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Great question and response. I've learned to adapt to the change but I always wondered why it drops so low. It sounds like I need to purchase yet another gadget for my beer.

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Old 05-07-2013, 03:02 AM   #4
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You don't need to buy anything if you have time to spare. I found that you can set the temp higher than you want, slightly lower than ambient temp. From there every couple minutes drop the temp a degree or two, wait for it to level out and work down to your required temp.

Just don't forget that yeast fermentation is an exothermic reaction, meaning it gives off heat. Often ten degrees higher than ambient temp. You want your beer at that temp not the air in the box. A fermentation chamber, unlike a keezer, is more beneficial if you find a way to monitor the beer not just a bucket of water that doesn't have the extra heat from fermentation. Many people (myself included) tape the probe to the carboy or bucket and put insulation, bubble wrap etc, outside the probe to let it take the temp of the beer only.

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