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  1. #1

    thermal runaway test - this is why you don't leave a printer running unattended

    this is a test i have done recently to simulate the worst case scenario where a thermal runaway (mosfet failure) couple start a fire

    timelapse version:


    realtime video version:

  2. #2
    Super Moderator Geoff's Avatar
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    That doesn't look good...

    Can you please tell me the scenario this might happen? I never leave my machine overnight running, never have.. not for fear of this, but just for fear in general lol..

    I run pretty much all my gear on limiting devices, so pretty much everything runs of an independant circuit breaker, and the house has a thermal fuse set. Would a circuit breaker not detect a thermal runaway? I have never had a mosfet fail and blow on me, but it looks pretty violent.. I assume you did this outside with a 12v DC power supply and no breaker? have you tested it with one?

  3. #3
    It would be interesting to try a test with the thermal runaway protection in the Marlin firmware, just to confirm it works. I'm trusting it at the moment, but it would be good to have documented confirmation.

  4. #4
    Super Moderator Roxy's Avatar
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    Quote Originally Posted by 3dkarma View Post
    It would be interesting to try a test with the thermal runaway protection in the Marlin firmware, just to confirm it works. I'm trusting it at the moment, but it would be good to have documented confirmation.
    Its good that is in there. BUT... And its a big 'But'. What happens if your controller board locks up? No firmware is running. Or what happens if your sensors fail but not in a way the firmware can detect the failure. I'm real nervous about leaving mine printing unattended, but its not so much from the fire stand point. I'm worried it is going to go crazy and tear itself apart.

  5. #5
    Senior Engineer
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    The thermal runaway protection cannot protect against a blown MOSFET. It should protect against a faulty thermocouple or thermistor. Stratasys put a resettable thermal fuse on the top of the head specifically for this eventuality. They also put one in the chamber to protect against stuck chamber heaters.

    The printers and parts of printers that you buy should, by law, be CE marked in Europe (same thing, different standards for the US) and for the most part they are not. They may display the CE mark but painting it on and adhering to the rules that allow you to paint it on are very different. It is easy to spot things that would never pass the official CE testing.

  6. #6
    Engineer-in-Training
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    Yikes, the aluminium block melted.

    I wonder if it would be possible to make one of the heating cartridges legs have a thermal failsafe, for example use a solder bridge that would melt and break the circuit if the temperature is too high, or simply keep the wire under tension and if it gets hot enough to melt the solder it would also break the circuit.

  7. #7
    Engineer-in-Training
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    Probably easy to insert a thermal fuse into the wire that feeds the heaters(s).

  8. #8
    Technician
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    I've been meaning to add a smoke sensor to my printer that will shut down the printer and alert me if there is flame or smoke. Just haven't gotten around to doing it.

    Next step is to add a CO2 fire extinguisher or something similar that will trigger also.

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