In alt.engineering.electrical DaveC wrote:
The relay, powered by mains, simply opens the wireless sensor's sense
circuit when power goes away. I just want it to do so after waiting a
few minutes to see if power comes back on.

Can you use a solid state relay or a DIP relay, instead of the
presumably larger relay you're using now? If so, the coil current
will be much less, and you might be able to get away with something
like a wall transformer, a big capacitor, and the relay. The time
delay won't be very exact, but it may work for your application.

Matt Roberds