Date: Thu, 30 Mar 2006 23:00:40 -0500
Reply-To: robert shawn feller <feller@CARBONCOW.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: robert shawn feller <feller@CARBONCOW.COM>
Organization: carboncow
Subject: Re: electrical experts: voltage drop and the fridge theory.
In-Reply-To: <000001c65476$a8c1b8e0$6400a8c0@masterpc>
Content-Type: text/plain; charset="us-ascii"
Yea I met 100 amp hour (and you are correct it is a 1000 MCA).
I didn't realize the thermostat is out of the loop but now that I look I
understand. It is obviously because of the way VW wanted the 12v power only
when the car is started, which explains why the battery drains so quick! No
cycling to help recover...damn. I'm used to the compressor (traditional
refrigerant) on my boat where I can run the fridge all weekend on the water
with 12v. I was thinking I would have to replace this fridge but since I've
got it working I'm going to try to work with it. If I have to replace it
with a traditional Norcold I want a 12v unit that will cycle on/off duty and
will already have the robust charing/deepcylce system to support it.
I'm not really relying on the alternator to help as I have installed a
marine 110v charger, battery combiner and am rewiring the setup to something
more useful for my needs.
The wiring I am referencing for the voltage drop is the stock wire, which I
do not know the gauge of but I suspect it could be a bit heavier, nothing on
my boat looks this thin for something that pulls amps!
Thanks.
Shawn
-----Original Message-----
From: Dennis Haynes [mailto:dhaynes@optonline.net]
Sent: Thursday, March 30, 2006 10:53 PM
To: 'robert shawn feller'; vanagon@GERRY.VANAGON.COM
Subject: RE: electrical experts: voltage drop and the fridge theory.
I seriously doubt that you got a 1,000 amp hour battery. That would fit
in a forklift and weigh about 600-700 pounds. Maybe you got 1,000 marine
cranking amps? The 12 volt and 110 volt heating elements are both 70
watts. Both will work the same assuming you are maintaining proper
voltage. The only difference with the 12 volt is that there is no
thermostat control. The major drawback of the 12 volt is that when only
the battery is supplying power, the voltage will drop and the heaters
effectiveness drops quickly. Basically, except when the engine is
running, there is no reason or advantage to using the 12 volt long term
on an absorption refrigerator. Large RV refrigerators don't even install
that option these days. Keep in mind that it would take some effort to
get the battery charged I this application. After all the loses and
using only the alternator to charge the battery, figure only 50% rated
amp/hours being available.
For voltage drops across the wiring, you do not say what gauge wire you
used. 12 gauge wire would be the minimum for this heating application.
The stock wiring is designed with the consideration the 13.8 volts is
available with the engine running. By the way, the wiring from the
alternator is also undersized.
Dennis
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf
Of robert shawn feller
Sent: Thursday, March 30, 2006 9:02 PM
To: vanagon@GERRY.VANAGON.COM
Subject: electrical experts: voltage drop and the fridge theory.
I am amusing myself since I've been fixing and testing the fridge on the
bench. It's staying cool to 30 degrees on 110v for me. I just bought a
new
1000amp hour deep cycle for the new wiring I'm doing in my westy related
to
other needs then the fridge.
I figured I would hook it up to the fridge to just see how horrible a
job it
does (we all know 12v and the fridge are not the best friends). I should
get
a good day out of it based on calculations.
Here is my question:
The voltage at the battery (under load) reads 12.4 volts but at the
terminal
it reads 11.5 volts, only 3 feet of wire between the battery and this
terminal! Is the inefficiency of the battery cooling the system do to
improper low gauge wiring?
Seems to me that if there is 7% voltage drop in such a short run the
wiring
gauge for the heating element and the wires to the battery could be
improperly rated. This would then affect amperage and thus the final
wattage
(which is supposed to be the same as the 110v) is never achieved. I
would
assume those of you keeping the battery under the seat and running more
length of wire then I would have slightly more drop.
If I recall from my boat wiring days a 3% drop is the recommended goal
for
any length of run from the governing body for boat builders but as high
as
9% for least acceptable.
Any thoughts.or do I not know what I'm talking about!
Shawn
