No, you should not use a thermal fuse.

The PPTC resettable fuse after it trips the first time, doesn't return to it's former low impedence state for a long time. Sometimes hours, sometimes days, sometimes years. As it maintains its higher resistance even though the system is not in an over heated state, the fuse will trip faster the next time. This could lead to false positives during print or other operation.

The resetting will often not take place even if the fault alone has been removed with the power still flowing as the operating current may be above the holding current of the PPTC. The device may not return to its original resistance value; it will most likely stabilize at a significantly higher resistance (up to 4 times initial value). It could take hours, days, weeks or even years for the device to return to a resistance value similar to its original value, if at all.

https://en.wikipedia.org/wiki/Resettable_fuse

Currently, I am investigating the use of a hall effect current sensor and some circuitry. Based on the duration and magnitude of the current, a small capacitor is charged. When a threshold is reached (as determined by a voltage comparitor), the power is withdrawn to let the capacitor discharge (and the heating element cool). This should keep the heating element from reaching a temp above a configurable maximum.

Yes, you should use a thermal fuse. But only to protect the board itself from an overheating condition. PTC fuses however; is a no.

The PTC resettable fuse after it trips the first time, doesn't return to it's former low impedence state for a long time. Sometimes hours, sometimes days, sometimes years. As it maintains its higher resistance even though the system is not in an over heated state, the fuse will trip faster the next time. This could lead to false positives during print or other operation.

The resetting will often not take place even if the fault alone has been removed with the power still flowing as the operating current may be above the holding current of the PPTC. The device may not return to its original resistance value; it will most likely stabilize at a significantly higher resistance (up to 4 times initial value). It could take hours, days, weeks or even years for the device to return to a resistance value similar to its original value, if at all.

https://en.wikipedia.org/wiki/Resettable_fuse

Currently, I am investigating the use of a hall effect current sensor and some circuitry. Based on the duration and magnitude of the current, a small capacitor is charged. When a threshold is reached (as determined by a voltage comparitor), the power is withdrawn to let the capacitor discharge (and the heating element cool). This should keep the heating element from reaching a temp above a configurable maximum.

No, you should not use a thermal fuse.

The PTC resettable fuse after it trips the first time, doesn't return to it's former low impedence state for a long time. Sometimes hours, sometimes days, sometimes years. As it maintains its higher resistance even though the system is not in an over heated state, the fuse will trip faster the next time. This could lead to false positives during print or other operation.

The resetting will often not take place even if the fault alone has been removed with the power still flowing as the operating current may be above the holding current of the PPTC. The device may not return to its original resistance value; it will most likely stabilize at a significantly higher resistance (up to 4 times initial value). It could take hours, days, weeks or even years for the device to return to a resistance value similar to its original value, if at all.

https://en.wikipedia.org/wiki/Resettable_fuse

Currently, I am investigating the use of a hall effect current sensor and some circuitry. Based on the duration and magnitude of the current, a small capacitor is charged. When a threshold is reached (as determined by a voltage comparitor), the power is withdrawn to let the capacitor discharge (and the heating element cool). This should keep the heating element from reaching a temp above a configurable maximum.

No, you should not use a thermal fuse.

The PPTC resettable fuse after it trips the first time, doesn't return to it's former low impedence state for a long time. Sometimes hours, sometimes days, sometimes years. As it maintains its higher resistance even though the system is not in an over heated state, the fuse will trip faster the next time. This could lead to false positives during print or other operation.

The resetting will often not take place even if the fault alone has been removed with the power still flowing as the operating current may be above the holding current of the PPTC. The device may not return to its original resistance value; it will most likely stabilize at a significantly higher resistance (up to 4 times initial value). It could take hours, days, weeks or even years for the device to return to a resistance value similar to its original value, if at all.

https://en.wikipedia.org/wiki/Resettable_fuse

Currently, I am investigating the use of a hall effect current sensor and some circuitry. Based on the duration and magnitude of the current, a small capacitor is charged. When a threshold is reached (as determined by a voltage comparitor), the power is withdrawn to let the capacitor discharge (and the heating element cool). This should keep the heating element from reaching a temp above a configurable maximum.