Liberty4Ever wrote:If the thermal fuse is used to prevent an overtemperature condition in an extruder, it'll completely shut off the extruder heater. If the errant controller keeps trying to extrude, it could damage the extruder. Better than a fire, though. A thermostat would cycle the extruder heater off if it became too hot but would let it stay hot enough to extrude plastic without damaging the extruder. It's essentially a backup thermal controller, at a higher (but safe) temperature.
Small bimetallic thermal switches with a fixed temperature should be not much more expensive than a thermal fuse.
Liberty4Ever wrote:It's late here too! I was thinking, "Don't you hackers ever sleep?!?"
WRT the thermal fuse - go for it! That's what building stuff is all about. Everyone has different wants and needs... and even aesthetics. I didn't intend to come across like a jerk. I was just trying to give a fairly complete answer, and maybe mention some aspects you might not have considered.
I'm considering the thermal runaway problem as well. The smaller wattage resistors for extruder heaters are probably inherently safe. 100% duty cycle probably wouldn't cause a fire or do much serious damage. The higher wattage cartridge heaters can get very hot. If the extruder is mostly metal and all nonflammable parts, it might glow red but probably wouldn't ignite. But I think it'd be prudent to limit the temperature to something a bit above the maximum you'd ever want for extrusion if using those cartridge heaters.
I may look into inexpensive bimetallic thermal switches. If I find anything that looks promising to me, I'll post in this thread. For now, I'm busy trying to finish a CNC project so I can get back to my neglected mostly-built Hadron.
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