Date:         Tue, 7 Aug 2007 12:51:50 -0600
Reply-To:     Martin Jagersand <jag@CS.UALBERTA.CA>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Martin Jagersand <jag@CS.UALBERTA.CA>
Subject:      Re: Deep cycle batteries, voltage regulators, and eating cake
In-Reply-To:  <20070806175916.3D2922800C@fleet.cs.ualberta.ca>
Content-Type: text/plain; charset=ISO-8859-1

Warren Chapman <vwsyncroguy@YAHOO.COM> writes:

> I like this discussion very much ...also being very protective of every
> square inch of storage spacy in my Westy.....I like the theory
>
>.....but will a battery at 12V even start the vehicle?? I've recently read
> that a normal cranking battery is 50% gone at 12.3V and dead at 12V....so
> does a deep cycle still have cranking power at only 12V.

This would vary with a lot of factors. I guess the manufacturer of the
"battery protector" would put the breakpoint at a voltage where they would
think most batteries would still start most vehicles. But Canadians with
Diesel engines beware! As mentioned in another post one can up the cut out
voltage by putting diose(s) in series with the sense wire.

> Another point,...if the batteries were of the type that could be safely
> discharged to 80%.... then could 30% more of the house battery capactiy be
> used after the cutout ....giving even more useful AHs.


The point of putting the battery protector between battery 1 and battery 2
is
exactly to let you use 50% of battery one, and up to 100% of battery 2.
If you put battery 1 and 2 in parallel and the protector after that you will
use
50% of each battery.

On 8/6/07, Geza Polony <gezapolony@sbcglobal.net> wrote:
>
> Here's another wrinkle in the whole equation (to mix a metaphor): the
> voltage regulator/alternator system doesn't seem to be adequate to keep
> the
> batteries charged.
>
> If you're using a battery charger on the bench (or bedroom floor) to test
> a
> system, it doesn't seem like you'd get the same results as in the real
> world, where your alternator is trying to power umpteen things and charge
> two batteries at the same time.


BTDT crossing the rockies  and being hit by a Sept icestorm in 2000.  When
driving
got too difficult we pulled over and examined our options over a snack.
Heater fan on max, rear defrost on, wipers on etc. When getting back in the
drivers seat I saw the alt light shining bright red. A voltage check
revealed not
much left in battery, and alt not charging. Had a couple of my spare gel
cells
with me. Hooked these in and managed to drive out of the rockies and into a
nearby
indian reservation in Montana. I thought I might have shot the alternator,
but while
driving around unsuccessfully looking for one in rural Montana, it came back
to life.

Lesson learned: The standard 65A alternator in many of the early T3 has to
be babyed.
Nowdays when driving I always go light on the loads, especially if I also
expect to
charge the batteries.

By contrast, I've not (yet) managed to overload the 120A alt in the '94,
despite having
more electric loads in that Westy.

So does this mean we all should go look for a new stronger alternator for
our T3's?
Not necessarily. Much of our use is weekend and other shorter trips, going
to
a place, camping, then going home. The best strategy then is to fully charge
the
batteries with a battery charger directly after coming home. A couple of
hours drive
back on Sun evening isn't going to recharge a battery bank fully no matter
how
powerful the alternator is. I often forget post-charging, and the result is
that my
batteries sit being partially discharged for long periods between trips.
Letting a
lead-acid battery sit in a discharged state is worst thing one can do. It
will shorten
battery life significantly.

Martin

--
Martin Jagersand
University of Alberta
http://www.cs.ualberta.ca/~jag/