> I'm not sure if such a thing exists, but really want to get a relay circuit
> that keeps power to a device on for some preset amount of time (say, 1 hour)
> after input power has shut off.
>
> Why do I want such a thing?  I want to wire it up into the 12v supply for
> the fridge, so that I can have the fridge running on 12v, and make short
> stops for gas/lunch/whatever without the fridge losing power, but also
> without me running the battery down because I forget to shut it off.
>

I have a couple 30 minute Intermatic wind-up timer switches in my work
Vanagon for powering up the inverter and DeWalt battery chargers,
respectively. Crude, but highly effective and nearly indestructible.
Apparently even a battery charger trickling a charged battery and an
inverter with no load will drain an auxiliary battery FAST when you
forget to turn them off. Ask me how I know. The only drawback to the
Intermatics is that they're designed for 120V applications so they're
BIG--- single-gang electrical box big.

If you're looking for something electronic, I think the Altronix 6062
timer module would be ideal. It's designed for alarm and access
control stuff and the relay is limited to 8A, so you might have to use
its lower amperage relay to fire a larger relay that can handle the
fridge's power draw. The timer is adjustable from 1 sec to 60 min,
comes with good instructions, and can generally be found for less than
$20. Google "Altronix 6062".