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Date:         Wed, 5 Aug 2009 21:50:24 -0400
Reply-To:     David Beierl <dbeierl@ATTGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@ATTGLOBAL.NET>
Subject:      Re: Vitrifrigo trip results, wiring, battery life,
              charging issues, etc
Comments: To: mark drillock <mdrillock@COX.NET>
In-Reply-To:  <4A7A0F1E.7070601@cox.net>
Content-Type: text/plain; charset="us-ascii"; format=flowed

At 07:00 PM 8/5/2009, mark drillock wrote: >The important lesson for people to understand is the voltage can seem >fine when little charging is needed but after the battery gets run way >down you find out the wiring can't fill it back up fast enough because >the current flow is low.

To amplify this a little bit -- the main problem is that VW chose to use an alternator/regulator with internal voltage sensing on a vehicle with long cabling runs. Since the internal sensing is based on the proposition that cable losses can be ignored (because the cable is only a couple feet long) this was an unfortunate decision on VW's part. The correct method is to use a separate wire from the battery positive terminal or nearby directly to the regulator so that it knows what voltage the battery is actually seeing. It will then regulate the alternator to produce the correct results at the battery, automatically compensating for cable losses because the cable is now *inside* the control loop.

Done that way, an inadequate charging cable will waste a certain amount of power, and a really inadequate one will overheat; but unless it fails catastrophically the battery will receive the actual charging voltage that the regulator is built to deliver.

-- David Beierl - Providence RI USA -- http://pws.prserv.net/synergy/Vanagon/ '89 Po' White Star "Scamp"


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