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Date:         Thu, 30 Mar 2006 23:35:35 -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.
Comments: To: Dennis Haynes <dhaynes@optonline.net>
In-Reply-To:  <000001c6547a$6bc0d260$6400a8c0@masterpc>
Content-Type: text/plain; charset="us-ascii"

I agree and I figured most on this list would mention using the propane too but I think there are times we will want to make a quick stop (not have the propane on while driving) or maybe it will have trouble staying lit, or we have trouble getting it lit and then I have to deal with the wife complaining we are late for dinner while I try to light the fridge...just covering all my bases. Always be prepared! Since I'm putting a beefier deep cycle in for my needs I might as well try to make the 12v fridge system work in my favor too.

My theory is the battery is there to use it and I do have the 110v charging system I installed again for recharging the deep cycle while at camp at night too.

I don't see why the 12v couldn't be run though the thermostat too (if it would in fact cycle which I doubt) but I noted a .4v voltage drop just from the punch down, through the switch to the element...in about a 8" run of wire!! Running the 12v even more distance through the thermostat 6 more inches will have more voltage drop!

Most like my efforts are in vain but I had no interest in using the westy relay for charging and wanted my own 110v charger for other needs. If I'm doing this much work while the van gets restored why not. I learned from my new used boat that most of the 12v aux system (wiring and connectors) needed replaced on a 22 year old cruiser. I had considerable voltage drop issues common to old low end boats. I just took this view on the van and decided to consider the concerns of older wiring for aux systems too.

Shawn

-----Original Message----- From: Dennis Haynes [mailto:dhaynes@optonline.net] Sent: Thursday, March 30, 2006 11:20 PM To: feller@carboncow.com; vanagon@GERRY.VANAGON.COM Subject: RE: electrical experts: voltage drop and the fridge theory.

Why not just let the fridge run on propane? It uses very little and the bottle will run it for almost 3 weeks. The only time you need to turn the propane off is during refueling. So, for those long extended drives where you are stopping for fuel every 4-5 hours, run it on the alternator. Otherwise, just let it run on propane or if shore power is available, run it on 110v, especially if it is free. Battery power is not free. The alternator needs HP to charge a battery. Also, each time you cycle the battery, you reduce its life.

Dennis

-----Original Message----- From: robert shawn feller [mailto:feller@carboncow.com] Sent: Thursday, March 30, 2006 11:01 PM To: 'Dennis Haynes'; vanagon@GERRY.VANAGON.COM Subject: RE: electrical experts: voltage drop and the fridge theory.

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


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