holding temp with temp control

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roofman70 said:
has anyone been able to hold temp to an exact degree with a mini fridge and a temp control ?

if so how?


Nothing is exact. Different parts of the fridge will be at different temperatures. The built-in thermostat on refridges is pretty poor, so most homebrewers will overide it with a temperature controller purchased from a HB supply (Ranco, Johnson, etc).

Every temperature controller works on a thermostat design, which has a high point where cooling turns on and a low point where cooling turns off. These have to be separated by a degree or two, to avoid rapidly switching on and off.
 
My freezer-based kegger (Ranco controller) has ranged from 33.4F to 34.7F over the last month, according to the min/max monitor. I doubt any consumer system would do much better. By contrast, the fermentation cabinet (fridge with Ranco) is lucky to hold within a 3F range.
 
The problem is you probably have your controller's sensor in the air or in some water. The beer itself is generating heat as it ferments. Your controller has no idea this is happening. You have two options;

1. Get a thermowell so you can put your sensor IN the beer.
2. Tape the sensor to the side of the fermenter (second best but better than nothing).
 
Bobby_M said:
2. Tape the sensor to the side of the fermenter (second best but better than nothing).

That's what I do and I get a 8 to 9 degree delta when fermentation is going.

This has worked well so far, till I get a thermowell and drill another hole in the bucket lid.
 
ranco sensor is in the air. set at 68 degrees

have carboy full of water with meat thermometer through bung hole to read temp of water. reads 72 degrees

have fridge thermometer next to carboy. reads 64 degrees

have fish tank thermometer on carboy. reads 69 degrees

wich would you belive??
 
Bobby_M said:
The problem is you probably have your controller's sensor in the air or in some water. The beer itself is generating heat as it ferments. Your controller has no idea this is happening. You have two options;

1. Get a thermowell so you can put your sensor IN the beer.
2. Tape the sensor to the side of the fermenter (second best but better than nothing).


if the sensor is in the beer wouldnt the fridge run till beer temp comes down

if so then wouldnt the fridge temp be enough to bring beer temp down below where we want it
 
I guess the question is, are you more concerned with the air temp inside the fridge or the temp of the beer in a particular carboy? If the beer (which matters most for fermentation control) then the sensor needs to be IN the wort.
 
You get a more accurate temp reading if the thermometer is in the beer. That doesn't mean its the optimal control.

I think roofman is right. If you have 5gal of beer at 70df, and the temp probe is in a thermowell, and the tyhermostat is set to cool until 68df, then the controller will run the fridge full steam until the beer is down to 68df. At which point the rest of the interior of the fridge will be really cold. This could cause you to undershoot the temperature, as well as waste a lot of electricity.
 
im trying to control the temp of the liqiud

i want to ferment the liquid at 70 degrees consistant

i havent been able to do that yet

if i put the sensor in the liquid the fridge will run to -20 degrees + that is not what i want to happen.

still tinkering
 
roofman70 said:
im trying to control the temp of the liqiud

i want to ferment the liquid at 70 degrees consistant

i havent been able to do that yet

if i put the sensor in the liquid the fridge will run to -20 degrees + that is not what i want to happen.

still tinkering

You are running into this problem because of the thermal mass of 5g of beer. If you want it to be 68F and it is 70F then your fridge will drop the temp down cold until the beer temp falls to the desired temperature - which will take time (hours). After that the fridge will run very intermittently and not create such a large temperature gradient.

GT
 
StewJo said:
You get a more accurate temp reading if the thermometer is in the beer. That doesn't mean its the optimal control.

I think roofman is right. If you have 5gal of beer at 70df, and the temp probe is in a thermowell, and the tyhermostat is set to cool until 68df, then the controller will run the fridge full steam until the beer is down to 68df. At which point the rest of the interior of the fridge will be really cold. This could cause you to undershoot the temperature, as well as waste a lot of electricity.

Since it's the beer temp that you really care about, I don't care one bit what the fridge has to do to get me the temp I want. I believe the ideal situation for a unit meant for fermentation control, is to get your sensor in a thormowell that sits inside the fermenter, but relatively close to the outside of the vessel. You're right StewJo, the fridge is going to run until your fermenting wort gets to your set temp. If the fermenter is the only thing you have in the fridge, it absolutely has the most thermal mass. Once the set temp is acheived, the compressor will be shut off and the wort will not continue to cool past that point. Even if the air inside the fridge is 10F colder, it is no match for 5-6 gallons of liquid. If you put your controller's sensor in the air or even in a vessel of liquid separate from the wort, it will never coincide with the wort's temp because it's creating its own heat.

Say you have it in a jar of water and set temp is 70F. It will basically get that water to 70F and stop. Meanwhile your fermenting wort might be churning at 75F.

Now, let's say your sensor is in a thermowell in the wort and you have a jar of water in the fridge also with a thermometer in it. You set your controller to 70F. Now your thermometer in the jar of water might read as low as 65F because it's reacting quickly to the colder air temp in the fridge. Big deal... you want it to run so the wort is at the set temp, not anything else.

If you're only controlling a kegerator, the beer will not generate any of its own heat anymore. In that case, it's better to put the sensor in a small vessel of water to act as a slight buffer for when you open and close the door.
 
I agree with what you say, and yes, the thermal mass of the beer is much greater than the air and interior walls and fixtures of the fridge. So if the only thing you care about is the fastest route to cooling beer, then yea, go ahead and put the probe in the thermowell.

This is an inefficient method, however, because you'll be running the compressor on the fridge full out, dropping the interior temp way down, and sucking a lot of heat through the couple inches of insulation that surrounds the fridge box. I very much doubt that cooling the beer is of such urgency to justify the resulting utility bill.

Just my humble opinion.
 
I have been lagering in a small chest freezer with a thermowell and a digital johnson controller, I set the controler for 50 +-1 and over the last 2.5 weeks I have seen it from 46 to 52, when the sensor calls for cooling it freezes till it hits the target and shuts off, it will then continue to cool the beer to 4 degrees below ideal. If i set it to 52 then the temp is sometimes as high as 54 so i leave it holding my lagering between 46-52 I would say the average has been 48 or 49.

I just finished transfering into my secondary and will lower the temp a couple degrees a day till I reach my target of 34, I am assuming the temp range will be much closer at teh lower temps, I guess I'll find out next week.
 
If you want your beer to ferment at 70, and it's actually fermenting at 76, you might as well not use a fridge or controller at all. But that's just my opinion. If you want to be really efficient, you can only brew when ambient temps are desirable for the style like they did in the old days.

Superior, I think you're seeing why the sensor placement is really more a compromise rather than a one size fits all. For a lager though, the fermentation doesn't likely generate that much heat. In your case I'd probably put the sensor in a small body of water such as a white labs yeast vile. It will react faster but still provide a buffer.
 
Thanks for all the input everyone.
After playing around for a week i have found the sweet spot that i am happy with.
Going to brew a weizenbock today and see how this thing holds up.

Thanks agian and Happy Brewing All!!!
 
If you want to get better temperature control of the ferment then connect your temperature controller in series with the operating thermostat for the cooler. set cooler thermostat at least 10 degrees cooler than desired ferment temp and temperature controller to desired fermentation temperature. Use a heatsink compound on temperature controller element and tape to side of fermentor, then cover with a 6" square of 1" foam rubber or other insulation to isolate sensor from air temperature. In operation the controller enables the cooler thermostat which will limit how cold the cooler will get until the controller is satisfied and should with a bit of experimentation with the cooler thermostat get you fairly good temperature regulation of the fermenter.
 
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