Zach:

> Jim, Yes, I agree a thermostat would be better, but some might see this as
> "too complicated".

It would be simpler.  The bi-metalic cut-out would insure that the current
passed through the wire was "enough", and cut off the current at the correct
time without a need to "time" the connection (but I must admit that your new
15-second design makes the task of timing much less taxing...).

> The trick is, will it still work inside the plastic (embedded --

It does not have to.  One would need only ONE bi-metalic thermostat, and
one could mount it on the battery, or otherwise between the power source
and frame.

The bi-metalic thermostat would be in series with the heating coil in the
frame.  While the two would heat up independently, the thermostat will
still heat up at a consistent rate, and deliver "X" joules before it trips.
Think of the whole set-up as a dead short with a slo-blo circuit
breaker, and it might be less complicated to visualize.  The circuit breaker
is never co-located with the short, but it still trips.

        jim

            Farmageddon (where we dream the dreams your stuff are made of)