The problem with the math, is it makes several assumptions about the
environmental circumstances that may or may not be valid. If it gets
cooler at night, such that the fridge compressor doesn't need to run
much (or at all), this throws off your timing. A similar issues
comprimises the longetivity timetable, if it is hotter that
anticipated. Opening the fridge a lot, will mean it cycles more. If
the fridge is more tightly packed, it will cycle less. Etc.

Lots of variables here.

On Jul 27, 2009, at 1:20 PM, Troy wrote:

> All I can say is do the math! Manufacturers Amp hour ratings on
> batteries tends to be optimistic and it has been said many times on
> this list and elsewhere that a standard lead acid battery should not
> be drained more than 50% routinely or you will kill it quickly. 20%
> or so is better. Deep cycle batteries can be drained more, but have
> their own set of problems, like needing a higher voltage to charge
> them completely and they are expensive.  A solar collector might be
> ideal for these as they produce higher voltages for charging.
> Admittedly, a 30 W solar panel is barely adequate for a vanagon. I
> believe that puts out something like 1.5 amps, maybe 1.8amps, and
> that's under ideal conditions. A MPPT controller can at least
> squeeze out every ounce of power if you have one. Personally, I
> would think something in the 80 to 90 watt would be much better, but
> I'm not a solar panel expert. Perhaps the squirrel guy could answer
> that one--Rocket?