Thermocouple Junction Placement

[tezcatlipoca]

Hey guys,

I'm new to the forum and new to homebrewing. I just modified my 2 year old mini fridge to serve as a fermentation chamber, later kegerator. For my first brew, I wanted to do a traditional bock, which is now lagering. I'm having problems with temperature control. I have a 4.4 cubic foot mini fridge with a etc 11100 controller by Ranco. The thermocouple has been found to be accurate when submersed in liquid at room temp.

Currently, I have it taped to a plastic carboy with metal tape, then plumbers putty and more metal tape. It doesn't read accurately like this(or with electrical tape). My beer is at 46 degrees now and my thermocouple is reading 32. Anyone wanna give some advice on how they've overcome this. Placing a thermowell in my beer is not really an option.

I thought about next taping it to the bottom of a plastic carboy. Or a have some of that hard styrofoam in sheets(can't remember what it's called) that I could use as insulation. I also thought about getting a water bottle and just sticking the thermocouple in there but I don't think that will get me to exactly where I want to be. Thoughts?

For now, my controller is set to 20 since I'm trying to lager at 35, but in the future I'd like to use this for accurate fermentation so I'm trying to work this kink out over the next 4 weeks or so...

 

[Brettomomyces]

Well, placing a thermowell into a carboy can work, check this out

http://morebeer.com/products/stopper-thermowell.html

There are lots of other varieties like this one. Submerging the thermocouple in a cup/bottle of water inside the fridge would be a good idea as well.

 

[tezcatlipoca]

I am familiar with that but I'm using the better bottles and already have all the upper pieces I need. I could buy more, but I really don't want to. I think I'll grab a water bottle now and try that out...


Beer, it's what's for dinner!

 

[IslandLizard]

There are 100s of posts on proper probe placement so the probe reflects the beer temperature. The metal tape is likely the culprit of it reading the ambient fridge temp rather than the temp of the beer in the carboy. Put a piece of insulation (e.g., 1/4"-1/2" stiff packing foam) over the probe and tape that to the vessel. I use regular 2" wide plastic "packing tape," without the threads. Or a bungee. Either works for me.

 

[rekoob]

+1 what IslandLizard said.
I normally just fold up a paper towel three or four times and use a piece of tape over that to tape it to the carboy, then ease the temp probe under the paper towel.
Works like a charm.

 

[tezcatlipoca]

Ok, I cut off a square of polystyrene I had in the attic(had to have been over 100 degrees up there). Cut a channel for the probe and taped the polystyrene to the vessel. I have that positioned between two vessels(taped to one), and it now reads 38, but let's give it some more time. I know the temp of my beer is 47 right now.

If it doesn't work in a couple of hours I'll add a paper towel to the mix. Thanks for all the help guys! I'm trying to get this resolved before end of day now that I'll be leaving it 'til Sunday(wife's grandparent died).

It now reads 35, so it is getting colder. Am I correct that only the junction matters(end of thermocouple)?


Beer, it's what's for dinner!

 

[day_trippr]

Jeeze, don't bother using paper towels if you have flexible foam!
The R-value of the former is peanuts compared to the latter.
I use inch-thick closed cell foam board scavenged from shipping cartons, roughly 4x6" pieces, for carboys in the ferm fridge and kegs in the keezer...

Cheers!

 

[IslandLizard]

What you want to achieve is to isolate the probe from the fridge environment and only measure that of the carboy. The probe should have as much contact with the carboy as possible. Flexible foam shapes around the probe without having to cut a recess into it and provides tension for close contact.

I put a piece of thick and stiff cardboard on top of the foam and use a bungee around the whole vessel, thus clamping the probe to the carboy. Tape doesn't always stick well. How do you know the temp of your beer is 46°F ?

 

[tezcatlipoca]

How do I know? I have a separate, non-contact thermometer that I trust. It's a pretty sweet thing and I placed the thermocouple in a cup of water(room temp) and they agree.

I think I need a more flexible styrofoam. My is pretty rigid and I don't think it's providing the isolation I need. Reading 33 now. Let me search for some flexible styrofoam. The fact that it is plastic should have nothing to do wit my difficulties, right?


Beer, it's what's for dinner!

 

[IslandLizard]

Styrofoam is rigid, you want semi-flexible closed cell packing foam, 1/4-1/2" thick. He or she who saves has something

You trust a non-contact thermometer to measure the beer temp inside a plastic carboy? How do you know what it's really measuring? I'd rather use my $14 CDN digital or that long stem analog one, both calibrated by immersion.

 

[tezcatlipoca]

I've been using this particular non-contact for years and it has always been consistent with other thermometers. I experimented a lot with it when I first got it because I didn't trust it or understand exactly what it is measuring. I must say: I think all the error people experience is from user technique. Well, that is, if you're not using the world's cheapest non-contact.

So, I had to leave my place before I started getting the results I wanted. I was able to get to where the thermocouple read correctly when I first out it on, but degraded a little slowly to ambient over maybe 15-20 mins. This tells me I'm headed in the right direction but perhaps need more/better insulation. I'll grab some packing peanuts when I get back home on Monday and report the results here. Thanks for all the help guys!!


Beer, it's what's for dinner!

 

[Smellyglove]

I don't know what this product is called in english. But I use the kind of "flexible soft styrofoam (not actually styrofoam)" you bring for tent-camping to sleep on. About 1/2" thick. They're dead cheap and one roll ("mattress)" will keep you supplied for years. Just cut off a 4x4" square and tape that round your probe to the carboy. Since they're flexible you can easily tape it to the carboy.

 

[singybrue]

Cut a 4x4" square off your lady's yoga mat!

 

[tezcatlipoca]

Haha, yoga...

Ok, I think I've resolved my problems. I'm still tweaking my set-up but it is working now. I appreciate all the help that was given.

I still need to add the fan to my setup but that shouldn't change things much.

I also picked up a thermowell for more accurate reads when active fermentation is occurring in the primary but I'll still be using creative taping with the secondaries...