> sounds like an excellent application for a "super cap", i.e. the very
> high capacitance capacitors designed for memory backup power

I do use super caps for a couple of memory circuits and find them
invaluable, but they wouldn't do in this case. Powering the circuitry
is not a problem, but operating the solenoid (4R load for 1/2s every
30 seconds) would quickly drain it. An SLA is not too expensive on
a cost/year basis

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