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Date:         Thu, 31 Jan 2002 15:14:20 -0800
Reply-To:     gary hradek <hradek@YAHOO.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         gary hradek <hradek@YAHOO.COM>
Subject:      Re: Red light rev(the Jolly guy from Rhode Island)
Content-Type: text/plain; charset=us-ascii

David and Andrew, Might not this deliberate design choice by VW be to prevent drag on the starter motor from the alternator during start up? Could make the difference in those cold Rhode Island winters as you crank away? "Better to light a red light than to curse a nonstarter" gary

>Andrew, > I may be wrong about this but I do not think >there exist a permanent magnet "weak or strong" in the >alternator. Increasing the engine rpm turns on a >electrical loop from the dash that provides power to >the alternator thus making the electromagnetic force >needed to make the alternator charge. The bearded >guy from back east can explain this better than I. >The jolly guy from cape cod. regards gary

Glad they're not talking about me (the cranky guy from Rhode Island). <g>

But FWIW, you're right. The old DC generators had a residual core magnetism that was necessary to remind them which direction to charge in, but alternators (except the "self-exciting" type) rely on an input current on the D+ terminal to energize the field enough to begin charging. The rpm at which this happens appears to be dictated by the amount of current you supply to the D+ terminal, other things being equal. So it appears to be a deliberate design choice by VW when they specified the bypass resistance that parallels the LED in the panel. Hanging relays on that line ought to raise the required rpm by diverting some of the current intended for the field (though probably not by much).

Ref. Bosch Automotive Handbook p. 809ff.

david

-- David Beierl - Providence, RI http://pws.prserv.net/synergy/Vanagon/ '84 Westy "Dutiful Passage" '85 GL "Poor Relation"

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