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Thread: Heatsnob Earthing Issue

  1. #1
    Senior Member brettreaby's Avatar
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    Heatsnob Earthing Issue

    Recently I fitted 2 heatsnob units to my Gas Roaster and a quite old Metal Chassis PC. I was getting message errors in Roast Monitor along the lines "Thermocouple short circuit power supply"

    Roast monitor software kind of worked but the readings were jumping around so much it was pretty useless.

    I checked the integrity of the earth of the PC, powerboard and Roaster all of which checked out OK.

    I also played with different USB ports, booster power units for the heatsnobs etc,

    In the end I fitted additional earth cables between the thermocouple braided wires and the chassis of the PC. This has totally fixed the problem.

    The Attached sketch shows the layout. Hope this helps anyone having a similar issue.

    heatsnob earthing.jpg
    MrFreddofrog likes this.

  2. #2
    Senior Member brettreaby's Avatar
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    And here's the setup with the PC connected, working well.
    Attached Images Attached Images

  3. #3
    Super Moderator Javaphile's Avatar
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    The problem is most likely with the earthing/power supply of one or more of the devices (PC and/or roaster), not the heatsnob itself. Doing what you did can get rid of the error but it doesn't really fix the actual problem.


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    Senior Member brettreaby's Avatar
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    Yes most likely the roaster itself has some earth current which create a potential between the earth of the roaster and the earth of the PC, upsetting the USB ports which are very sensitive to such potentials.

    ( I eliminated the heatsnob units as the problem early in the investigation when i disconnected the thermocouples from the roaster and the readings were steady.)

  5. #5
    CoffeeSnobs Owner Andy's Avatar
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    Quote Originally Posted by brettreaby View Post
    most likely the roaster itself has some earth current
    Yes, the title of the post isn't quite right. It's a roaster issue and the HeatSnob is just clever enough to diagnose it!

    Earthing the leads is a good workaround though, I'm sure that will help others. Thanks for posting it up.

  6. #6
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    I've had the same problem with various thermocouples. Did you check for continuity between the thermocouple wires and the braided/thermocouple sheath (it should be open)? That also results in the ground loop problems you're experiencing.

    In a laptop setup, the short term solution is to run the laptop on battery power while roasting. Longer term solution is to get a better quality MIMS thermocouple.

  7. #7
    Senior Member brettreaby's Avatar
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    Behmor Coffee Roaster
    The thermo couples were checked open circuit between the shield and the wires. At least at room temp never checked them at roast temperatures I might try that As well.

    Good reminder.

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