Why don't we have a thermal fuse in-line with the heater cartridge?

Discussion in 'OpenBeam Kossel Reprap and OpenBeam Kossel Pro' started by JoeF, Jan 16, 2015.

  1. JoeF

    JoeF Member

    As I learn more about 3D printing, it seems to me one of the most catastrophic failures is when the thermistor pulls out the hot-end, as it could cause the heating element to runaway and start a fire. I think that's why the the Kossel Pro hot-end has it epoxied on so well.

    Almost any appliance with heaters will have a 240C fuse right before the heating element in order to get certified. Why should a 3D printer be different? It would certainly make me feel better leaving a print running all night.

    It's probably tricky to get the right location and fuse temperature to prevent the head from being destroyed without causing a lot of false fuse failures. But for preventing a fire, I think just something conservative in-line with the input leads of the heater cartridge should suffice.

    What do you all think?
  2. Mike Ziomkowski

    Mike Ziomkowski Administrator Staff Member Vendor

    Thermal fuse is something we have considered but there are issues.

    1) 240C is a really the highest you can get for thermal fuse (not easily), which might be ok for our hotend but barely. You are right appliances do use cutoffs, but lets say your dryer, probably about 160C fuse
    2) Where to put it? There is not a good location for it, we considered placing it near the endeffector board, with lower cutoff, but realistically by time that blows, its too late.

    We are working on coming up with solutions that would protect against thermal runaway that dont involve a thermal fuse.
  3. JoeF

    JoeF Member

    I'm actually thinking more about safety. Even if it's near the end-effector with a lower cutoff, where it'll be too late to save the hot-end from melting, it may still prevent a fire. My understanding is that a runaway heater can get red-hot and actually melt aluminum.

    I saw the threads on dual thermistors. Is this what you are planning? I still think a thermal fuse is a good idea even then for fire safety.

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