AC Powered Heater Protection
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Self-resetting thermal cutoff. Keenovo will build them into heater(s), if you ask.
Delta / Kossel printer fanatic
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@samlogan87 I would add a thermal fuse to protect the bed from overheating even if the SSR fail shorted. Like the example on the photo that is rated to shut-down at 180C.
they are very common components used with coffee machines and other home appliances that use heaters.
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@danal
Self-resetting is not a good idea. There are two main reasons for excessive heating in the bed. Either the controller has lost its mind or the device switching power to the bed has failed. If you use a self-resetting thermal fuse it will keep cycling the power on and off, and will keep heating the bed excessively, possibly damaging the bed an other components, possibly leading to fire. -
@mrehorstdmd self resetting will just act as a poorly tuned bang-bang.
Temperature will rise above the fuse threshold, open the circuit, this will allow the temperature to cool below the reset threshold, the fuse will close allowing current to flow and the bed to resume heating until the temperature again rises above the threshold and the cycle repeats endlessly maintaining a temperature close to the two thresholds.
It is of course less than ideal as a dead stop in case of a fault is preferred, but depending on how the fuse is wired changing it may not be an easy task.
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@dino I wouldn't order a heater with a self resetting thermal cutoff. They are not thermostats- they are intended to be safety devices. I doubt that the self resetting devices are meant to operate over many cycles before the device fails (hopefully they fail open).
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@mrehorstdmd my example was also worst case, if there's a polyfuse or other latching type resetting thermal fuse it will continue to leak a small amount of current when tripped, maintaining its temperature and preventing itself from resetting until the current is removed. Like you said they are safety devices and are designed as such.
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That thermal fuse at the picture is not self-resetting
When you go over the specified temperature it just cuts the circuit for good. You need to replace them to work again. It is a last resource option for great safety. -
I'm the one with the self-resetting device, installed by Keenovo. Everyone's points are valid... it would cycle... and it could fail as well...
Nonetheless, given that it is a second or third layer of protection, I'm OK with that. You may not be.
Here is yet another layer of protection:
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@danal What type of self resetting fuse is it if you know? I kind of regret not getting one built into my bed, Even though I have redundant safety measures as well an extra one wouldn't have been bad.
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@dino said in AC Powered Heater Protection:
@danal What type of self resetting fuse is it if you know? I kind of regret not getting one built into my bed, Even though I have redundant safety measures as well an extra one wouldn't have been bad.
I don't know, it is/was embedded in the silicone by Keenovo, so I've never seen it.
