Date: Tue, 30 Jul 2019 21:22:25 -0400
Reply-To: David Beierl <dbeierl@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@GMAIL.COM>
Subject: Fwd: Dometic Fan
In-Reply-To: <CAMOH8LKNQNxw5xeUQYF-wufL-1Bch91RL-6RMZn-PEQEqC0wEw@mail.gmail.com>
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---------- Forwarded message ---------
From: David Beierl <dbeierl@attglobal.net>
Date: Tue, Jul 30, 2019 at 9:21 PM
Subject: Re: Dometic Fan
To: David Boan <dboan@outlook.com>
Cc: vanagonlist a <vanagon@gerry.vanagon.com>
On Tue, Jul 30, 2019 at 9:08 PM David Boan <dboan@outlook.com> wrote:
> I wonder what "working well" means with a dometic fridge, so I gathered
> some numbers. ...
>
> Running on 12v from the house battery, engine not running, for one hour,
> the temp of the cooling fins inside the fridge is 49 (measured with an
> infra-red sensor). The outside temp, both in my garage and inside the van,
> is 98. The temp on the outside of the fridge door is 96 (an indication of
> marginal cooling loss?).
>
> During that hour, the house battery went from 12.5 volts to 12.3 volts. I
> do not have resistance or amp data to know if this is reasonable. I
> anticipate running this from my solar panel, which will keep the battery
> charged during the day, but obviously not at night. I am curious to
> calculate how much the battery will be drawn down after 12 hours.
>
The fridge on DC will draw 7.5 amps continuous, with no thermostat.
>
> I then switched to 120v. Understanding the fridge was already cool, I
> wanted to see if 120v would get it cooler. After an hour the same spot
> (cooling fins) were 40. The outside temp was 97.
>
Run it for 24 hours on 120 VAC with thermostat turned to max to get your
benchmark. These fridges can't move much heat, so everything happens
slowly with them.
It's been a long time, but I think box temp (not fin temp) 40F below
ambient is doing pretty well. Someone will correct me on that. Keeping
the van ventilated with the skylight for a chimney effect and shading the
fridge side from the sun will help.
In reasonable weather they can make ice in the little toy ice trays.
Slowly.
One of the things that will kill performance is if the fins inside lose
intimate contact with the cooling tube. May help to pull the fin assembly
off, clean the old heat sink compound off both surfaces, and reinstall with
a *THIN* I mean Really Thin layer of compound. Ideally you want only
enough to fill the irregularities in the apparently smooth surface, because
heat sink compound is actually not a very good conductor.
In theory operation is equally effective on all three modes. In practice
DC tends to perform less well unless the wiring is absolutely tip top,
because a half volt drop at 12V is a much greater percentage than at 120V.
Gas normally works as well as AC. Again, there is not thermostat on DC.
Yrs,
d