Date: Mon, 22 Mar 1999 07:47:49 -0800
Reply-To: Davidson <wdavidson@THEGRID.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Davidson <wdavidson@THEGRID.NET>
Subject: Re: Dometic on 12 volts?
Content-Type: text/plain; charset="iso-8859-1"
Robyn,
There is no exact answer to your question because there are several
variables that depend on the circumstances. One of the variables is ambient
temperature. First, a battery will deliver the most amp hours within a
certain temperature range. Second, the hotter it is, the more the dometic
fridge thermostat will keep the heating element activated thus using more
power. Third, the colder you have the thermostat set the more often it will
have to use power. Another variable is how often you open the fridge door.
And I'm sure there are other variables that I haven't thought of this early
in the morning. All that said, here are some ruff numbers:
Although the Optima is rated at 65 amp hours at 20 degrees C, you can figure
ruffly that you will only get about 50 amp hours out of a new, fully charged
Optima before the voltage is drawn down to 10.5 amps. (I got this
information from one of the Optima tech guys.) There are three problems when
you take the battery below 10.5 amps.... (1) most appliances will not
operate well, (2) the battery drops off quickly beyond this point, and (3)
there is enough sulfidation beyond that point that bringing the Optima back
to a full charge of 13.1 volts is time consuming.
Okay, so figure on about 50 amp hour available from the Optima. The Dometic
uses between 7 and 8 amps per hour that the thermostat keeps the heating
element on. If we use 8 amps per hour, then you can figure that a fully
charged Optima will run the Dometic for about 6 hours (50 divided by 8 =
6.25) if the thermostat kept the heating element on constantly. So depending
on the average ambient temperature in a 24 hour period (and the other
variables mentioned above) that could mean that your fridge would be kept
cold for a day or so. Also, I'm not sure that the heating element will work
as well as the voltage drops. So it is possible that the cooling effect as
you drop towards 11 volts would be minimal.
Regarding the camper cabin light, it is *not* wired through either of the
two red wires that go from the auxiliary battery box under the drivers seat;
it is wired in with the dome light/radio/cigarette lighter/map light circuit
that comes off the main fuse panel. The choice would be to either change
this whole circuit over to the auxiliary battery or to isolate the wire that
goes to the rear cabin light. In my 90 Westy Syncro the wire to look for is
one of the red wires that come out from the hollow metal channel between the
windshield and the door opening. Pull out the fuse panel and look up and
left. This wire feeds both the dome light and the rear cabin light. If you
want to separate the two it involves fishing a new wire from where they join
at the dome light, down through the hollow channel. If you have run a new
(hopefully larger) wire from the starter battery to the auxiliary battery,
you could do as I did and use the old starter to auxiliary battery wire
(part that goes from the main fuse panel to the auxiliary battery box) as a
feed for this newly fished wire (or the wire that feeds both the dome light
and the rear cabin light). I found the end of the wire that goes from the
auxiliary battery box to the main fuse panel to be a female spade connector
attached to a male spade terminal at the rear left edge of the main fuse
panel. To confirm that you have the correct wire, just test the two
disconnected ends for continuity. As always, it is safest to have the
grounds wires disconnected from both batteries before mucking around with
the electrical system.
Good Luck
Bill
90 Westy Syncro
-----Original Message-----
From: Robyn Rudisill <robyn.rudisill@HOME.COM>
To: vanagon@GERRY.VANAGON.COM <vanagon@GERRY.VANAGON.COM>
Date: Monday, March 22, 1999 6:35 AM
Subject: Dometic on 12 volts?
>Vanagoneers,
>
>How long should I expect an Optima 12v deep cycle battery to last with the
>fridge on it?
>
>Also when I wired up the aux battery, I some how missed putting the stock
>camper lamp (the one in the back over the stove area) on the aux
>battery? Is that one of the red wires on the stock relay under the
>driver's seat?
>
>Thanks for your time.
>
>robyn rudisill
>91 Westy Syncro
>
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