Date: Thu, 20 Dec 2001 19:56:47 -0500
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: A twist on dual-battery configurations
In-Reply-To: <051301c189b2$0d5f54e0$3b47fea9@grumpy>
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At 06:57 PM 12/20/2001, Julian Burden wrote:
>When the engine (therefore the alternator) is running it shouldn't matter
>which battery the extra loads are connected to. When the engine is not
>running I want to keep the starter full (using headlights at the campsite
>etc).
Of course. I'm used to thinking in terms of boats...big lights and such
used for matters of seconds at a time.
>Yeah, but 120v open circuit is 0 amps = 0 watts. If you have the same
>current, but a higher voltage (caused by pushing through the extra diodes)
>the alternator does have to work harder. I actually see these two points as
>the one, I was rephrasing points made in the archives.
Ok, I concede that.
>I don't see this as a problem - Vf's will be within 0.3v - and I think mine
>will be the lower of the two (0.3 - 0.4v depending on temp) cable
>differences will reduce this gap (I'm not going to be using the same gauge
>as the starter cable!). Ideally the batteries should get the voltage they
>need, a variation from what they need is probably more important than the
>difference between the two batteries.
Agreed.
>No problem, I've already selected diodes and heatsinks whose rating is
>sufficient.
Are they going to be in the 150F ambient of the engine room? Not saying
you haven't done your homework, but these things do get overlooked...
>I don't like the bigger relay solution ("dumping" from starter to aux), and
A smart regulator setup would probably address this by not paralleling the
batteries until the house battery had achieved a certain voltage...but also
I think that the "dumping" problem is much overrated, i.e. not much
charging will occur until the alternator pulls the system voltage up above
13 volts or so, and once you get above 12.6 or thereabouts both batteries
should be accepting charge even if minimal.
>I don't see this as much more difficult (apart from the R&D which I enjoy)
>than the isolator and voltage sensing method.
I agree -- I just think it's a band-aid, and you clearly have the ability
to do it properly so why not...if you could design a proper 3-stage
regulator that cost $60 a lot of people would love you. :)
david
--
David Beierl - Providence, RI
http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"
