There are number of ways that batteries are rated. For the most part,
the amp/hour rating is for 100% discharge. You never want to go below
80% as some battery damage occurs. Using a constant-voltage regulated
charging system such as a vehicle alternator, you will rarely get the
battery over 85% state of charge. If you do, the top 10% disappears
within a few hours after charging stops. So basically, for extended
operation, only plan on 50-60% of the amp hour rating to be truly
available. Also, as the battery discharges, the voltage will drop. Will
that fridge even work at 10.5 volts?

For the duty cycle of the fridge, there are many variables. The major
problem with the van is the lack of ventilation when it is closed. When
the inside of your van is near 130F, that duty cycle may be near 100%.
If you use lights or the radio, you need to consider that also. VW went
to the trouble of that propane fridge for a reason. There just isn't a
more practical solution for refrigeration then and flame powered
absorption fridge.

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf
Of Malcolm Stebbins
Sent: Tuesday, March 14, 2006 6:08 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: 12V fridge necessary?

Actually, I'm about to go the other way.  I may remove my Dometic fridge
and put in an AC/DC
fridge that runs the Danfoss compressor.  These are advertised to draw
2.5 amps when running, but
they run for only about 15 to 20 minutes per hour and are advertised to
have an average draw of .5
amps per hour.

I don't understand much about electicity, but does that mean a 50 amp
deap-cycle battery  will run
a fridge that draws, on average .5 amps, for (50 amps/.5 amps) 100
hours?????  or is there some
unknown (to me) factor that makes this not true?

I posted my Alternative Fridge research here:
http://gerry.vanagon.com/cgi-bin/wa.exe?A2=ind0602D&L=vanagon&P=R10601

Malcolm

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