In article ,
Fred McKenzie wrote:

Rick-

I've seen photos of these ovens on E-Bay, that had been stained by smoke coming
out of the adjustment hole. I'd rather have some kind of protection.

I believe the oven uses proportional control, so the transistors' maximum
dissipation would occur when the heating element is half on. In a "runaway"
mode, the transistors would be switched on with maximum current but nearly zero
voltage. Also, one transistor failure mode is a short-circuit.

Seems like a self-resetting "Polyswitch" overcurrent limiter might be
a workable alternative. You'd probably want to pick one whose "will
pass" current is somewhat above the highest amount of current that the
oven would draw when it's quite cold. If the transistor shorts, and
the oven draws more current than that, the polyswitch would heat up
enough to go high-Z and chop off the current. Cutting power for a
minute or so would reset it.

--
Dave Platt AE6EO
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