> I just asked a question about battery capacity for driving a box fan
> overnight. The fan motor draws .8 amp, not the .5 I originally stated.
>
> Well, let's see... 0.8A * 120V = 8A * 12V. Figure on 10% coversion loss
through the inverter-- probably less, but best to be conservative-- making
it 8.8A draw. 8 to 10 hours of that  is from 70 to 88 Amp-Hours.  My group
24 Trojan deep cycle (a a very good battery), which is too big for under the
driver's seat and lives under the rear bench, is rated at 70AH (5 hour rate)
to 85AH (20 hour rate). So at an 8 hour rate I might be able to get 75AH out
of it. That'd leave it "mostly dead" every morning. Given how long it takes
to charge a battery up off the alternator, I'd say finding a low-amperage
12V fan might get better results. I've seen 2 or 3 of those black computer
fans mounted in a little wooden frame stuck in people's windows before. At
0.25A apiece, you could run a couple of those all night and only use 4-5AH.

--
John Bange
'90 Vanagon - "Geldsauger"