Thermal Runaway protection



  • I have a Duet WiFi v1.01 running firmware 1.19 on my Hypercube Evo.

    I had a thermal runaway occur during an autotune last night. Sometime during the heating phase the thermistor detached from the hotend with spectacular results:

    0_1540909190794_ThermalRunaway.jpg

    I was surprised that the firmware protections didn't disable the hotend. The heater cartridge completed destroyed itself before software protections kicked in. I've worked with Marlin a ton but this is my first go round with Reprap firmware. Did I miss something in configuration that could have caught this before it got out of hand? Marlin has been too touchy on PID tunes at times which is annoying but better than a meltdown like this.



  • @rj_mn I'd say that you were extremely unlucky in that the thermsitor failed during auto tuning. Normally it would be protected but from the Wiki here https://duet3d.dozuki.com/Wiki/Tuning_the_heater_temperature_control there is this............

    "Warning! During auto tuning there is minimal protection against heating faults. Therefore you should not leave the printer unattended during auto tuning."


  • administrators

    @rj_mn as @deckingman says the thermal runaway protection is disabled during heater tuning (only), in order for it to function as designed. For example the heater could be a special high temperature one like e3d are now selling. As the linked documentation and the warning in the firmware states, autotuning should not be left unattended!


  • administrators

    RepRapFirmware is used with a wide variety of heating systems, including ones for high temperature plastics such as PEEK and PEI. So one of the main purposes of auto tuning in RepRapFirmware is to establish the characteristics of the heating system, so that during normal use the firmware can better spot when it is not behaving as expected. Until you auto tune the heater, RRF doesn't know what to expect from it. So it does minimal checks during auto tuning - in particular, it checks that the temperature rises shortly after turning the heater on.

    The melting point of aluminium is 660C, so it looks like your heater cartridge was greatly over-powered. Were you by any chance using a 12V heater cartridge with a 24V supply?


 

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