Firmware safeguard prevent tuning MIC6 bed

  • Have a custom heatbed which is 1/4 inch MIC6. The bed dimensions are: 215mm X 410mm. Using a custom 120V silicone heater which is rated at 1000watt.

    All hardware safety measures in place including a bed mounted 120C thermal fuse.

    The thermistor is a Vishay encapsulated ring terminal type.
    Vishay thermistor specs: 100k B4190. The thermistor is mounted aproximately 30mm from the edge of the bed in the center. I can run a bare thermistor, but I am building 7 identical custom printers and the customer requested easy to swap out thermistors. The Vishay thermistors are also high quality and I do not want to run cheap bare thermistors from China as my client will only accept quality components that meet their industry specs.

    When tuning the bed the firmware will cancel because the temperature continues to rise. After canceling the tune the temp begins to fall at aprox 20 seconds after cancellation. I have tried varying the PWM and temp. Currently the closest I have come to meeting the timeout is tuning at 70c at 70% PWM.

    I have read other posts regarding issue. There was a firmware posted that had the tuning timeout increased to be able to tune a large mass heatbed with powerful heaters. The custom firmware is no longer available.

    Current firmware: RC 2.0

    Board: DUET Ethernet v2.0

    Vishay thermistor:

  • administrators

    I think your heater is rather over-powered for that size bed, hence the large temperature overshoot.

    You may be able to tune at a higher temperature if you use M143 to increase the bed temperature limit at least temporarily.

  • @Machine_Elite You might consider remounting the TCO on the heater instead of on the bed plate. If the heater comes off the bed plate, it will quickly get dangerously hot and may do some serious damage before the TCO on the bed plate gets hot enough to do anything. The adhesive on the Keenovo heater in my printer is starting to let go of the bed plate after about 1 1/2 years.

    I'll be moving the TCO from the bed plate to the heater, and attach it using high temperature silicone.

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