1. Stop lurking! Log in to search, post in our forums, review beers, see fewer ads, and more.

    — Todd, Founder of BeerAdvocate

Thermowell question

Discussion in 'Homebrewing' started by pweis909, Apr 16, 2016.

Thread Status:
Not open for further replies.
  1. pweis909

    pweis909 Grand Pooh-Bah (3,126) Aug 13, 2005 Wisconsin
    Pooh-Bah

    I had some egregious temp control problems in the last two batches -- my Ranco temp probe taped to the side of the fermenter got dislodged and I found beers to be about 30 F-ing degrees higher than I wanted! (The F stands for Fahrenheit). So I got a thermowell, thinking this would help ensure this never happened again. And I decided to test out my new method with water before I brewed another batch of beer...

    I filled a bucket fermenter up with 5 gallons of water last weekend and hooked my Ranco to a heat mat wrapped around the fermenter. I slipped the thermowell through the airlock grommet and slid the Ranco probe into the thermowell. Set it to 70 degrees, and came back a week later (today) and measured the water temp as 75 with my Thermoworks RTC600 thermometer. I calibrated the RTC600 against ice water and it is reading 32F, so I am inclined to believe the 5 degree difference between the actual water temp and the Ranco setting. I had a blanket over the fermenter thinking it would help insure against temp swings.

    What's the explanation for the discrepancy, do you think? Is the fix to just adjust the Ranco setting to lower than where I want it?

    Note: I am now testing it at 65 degrees, without the blanket. I'll check on it later this week.
     
    #1 pweis909, Apr 16, 2016
  2. VikeMan

    VikeMan Pooh-Bah (2,913) Jul 12, 2009 Pennsylvania
    Pooh-Bah

    Either that or calibrate the Ranco. I don't have any of that brand, so I don't know if it's possible.
     
    #2 VikeMan, Apr 16, 2016
  3. pweis909

    pweis909 Grand Pooh-Bah (3,126) Aug 13, 2005 Wisconsin
    Pooh-Bah

    Apparently not.
     
    #3 pweis909, Apr 16, 2016
  4. RashyGrillCook

    RashyGrillCook Initiate (0) Apr 30, 2011 Florida

    I use a Ranco as well. Mine is consistently 2 degrees high across the temp range. If your feeling brave, Rancos use thermistors so you may be able to adjust the resistance value in some way and bring that variance down a bit. Also, did you try taking a reading of the Ranco in ice water?

    Another problem may be stratification of temps. Water in a bucket that remains still will experience this stratification. Studies have been done on this with water heater tanks. If the probe was in the middle of the water and your heat source is on the outside then it will take some time for the heat to transfer through still water to the probe. At which point the outer edge has over shot the target temp. By the time all that heat energy has distributed you've gone way past your target point. This, of course, doesn't happen during active fermentation.
     
    #4 RashyGrillCook, Apr 20, 2016
    billandsuz likes this.
  5. Brew_Betty

    Brew_Betty Initiate (0) Jan 5, 2015 Wisconsin

    Have you tested the Ranco probe and the Thermoworks probe in the same temperature outside of the thermowell? That should tell you if the probes aren't in sync immediately.
     
    #5 Brew_Betty, Apr 20, 2016
    jbakajust1 likes this.
  6. CADETS3

    CADETS3 Initiate (0) Dec 3, 2014 Texas

    What kind of clearance is there between the ID of the thermowell and OD of the probe? If you don't have a nice slightly snug fit, that could be a reason as to a difference, but 5 degrees???
     
    #6 CADETS3, Apr 20, 2016
  7. jbakajust1

    jbakajust1 Pooh-Bah (2,456) Aug 25, 2009 Oregon
    Pooh-Bah

    I would be inclined to think it is the Ranco that is reading off. I would follow @Brew_Betty and put both probes into the same liquid at the same time and see if they read the same.

    Also, as @CADETS3 suggests, it could be reading inside the thermowell too. I put some foam in the top of the thermowell so that it doesn't get hit by the warm/cold air flowing down the thermowell from the heater/fridge and give a false reading.
     
    #7 jbakajust1, Apr 20, 2016
  8. Brew_Betty

    Brew_Betty Initiate (0) Jan 5, 2015 Wisconsin

    Thermally conductive grease in the thermowell eliminates this potential issue.
     
    #8 Brew_Betty, Apr 20, 2016
  9. pweis909

    pweis909 Grand Pooh-Bah (3,126) Aug 13, 2005 Wisconsin
    Pooh-Bah

    I haven't checked the Ranco in liquid, as my understanding is they are not designed for liquid immersion. So, I didn't test it directly against the RTC. It seems that removing the blanket helped. The readings were 1 degree apart after a few days. Like maybe the heating overshot the mark and then didn't cool down due to insulation?
     
    #9 pweis909, Apr 21, 2016
  10. pweis909

    pweis909 Grand Pooh-Bah (3,126) Aug 13, 2005 Wisconsin
    Pooh-Bah

    It's not super snug. It slides comfortably. When I bought the thermowell I had two diameters and had to go with the larger one that offers a few extra mm clearance. Maybe some foam in the thermowell makes sense.
     
    #10 pweis909, Apr 21, 2016
  11. VikeMan

    VikeMan Pooh-Bah (2,913) Jul 12, 2009 Pennsylvania
    Pooh-Bah

    Does your thermworks thermometer read air temps reliably? (My thermapen does, it just takes longer to settle than in liquid.) If so, just put the probes side by side in the same airspace and see how far apart they are.
     
    #11 VikeMan, Apr 21, 2016
  12. pweis909

    pweis909 Grand Pooh-Bah (3,126) Aug 13, 2005 Wisconsin
    Pooh-Bah

    Probably? I never really thought about how to reliably evaluate the temp of air as a calibration check, but I would think it reads the temp. Still, if I do as you suggest, I should at least know whether they read similarly in air or not, even if I don't know the actual.
     
    #12 pweis909, Apr 21, 2016
  13. RashyGrillCook

    RashyGrillCook Initiate (0) Apr 30, 2011 Florida

    Ranco probes are definitely not intended for immersion. If liquid gets into the probe it will greatly skew the resistance value of the thermistor. Someone mentioned thermal grease. If you must, sure, just make sure it is dielectric.
     
    #13 RashyGrillCook, Apr 21, 2016
    pweis909 likes this.
Thread Status:
Not open for further replies.