Date: Mon, 14 Mar 2011 22:59:51 -0400
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: Auxilliary batteries
In-Reply-To: <001601cbe2b5$56a08730$03e19590$@com>
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At 10:04 PM 3/14/2011, Daryl Christensen wrote:
>OK…My van charges at about 13.6 to 13.8 or9 max.
>All the spiffy temp/voltage AGM battery chargers I see are 120V AC input..
>Is there an onboard “charger widget” for upping
>the charge voltage to the 14.4 the AGB batts need?
Yes, but you're not going to like it. Because
getting up there is easy (at least on Bosch
alternators) - drop-in adjustable regulators are
easy to get. It's getting back down that's the
problem, 'cause if you keep the voltage up there
you'll boil the thing dry. Charging AGM and gel
deep-cycle batteries properly involves first
stuffing amps into them hard and fast until the
terminal voltage rises to {the right amount based
on battery temp}, then holding that voltage for
an hour or two, then dropping back down to the
{temperature-dependent} float voltage while the
engine continues to run. That means the
alternator will be running hard for a while,
either at its maximum output or at the maximum
rate that you have decided the battery bank can
safely accept (which is something like C/3 for
these batteries, C being the capacity in
amp-hours). It also means a much smarter
regulator than the ones used for cars.
The conventional way is to start with an
alternator that expects an external regulator,
and that also expects to be run hard. Here's the
setup my brother is putting in his Vanguard class
sloop, to be powered by a 30 hp Atomic Four engine:
Balmar 621, 70 Amp alternator and MC-612 multi
stage regulator with battery and alternator temp
sensors. Total damage just under $800.
Here's the Balmar lineup with list prices:
http://www.balmar.net/2011-Balmar-Product-Guide.pdf
===============================
The second way would be use the existing
alternator, modify it to accept external
regulation, and get one of the fancy regulators
from Balmar, Ample Power or another
supplier. That halves the cost at least. The
mod might be pretty easy - it wouldn't be very
hard on the Bosch to fake up the regulator module
so it was really mostly a brush carrier with the
smarts outside. And the alternator might be up
to the job, or it might need additional cooling
air supplied to the back of it to keep from
burning up. In addition to the continuous-duty
rating, the Balmar and similar alternators cost
more because they're what we used to call
explosion-proof, meaning they won't cause
one. Now they say "ignition-protected."
=========================
A third possible, a kluge, would be an inverter
driving one of the AC chargers you
mentioned. You'd have to determine whether it
would need to be a full sine-wave inverter or
would one of the cheap ones do. This would have
the virtue of giving you a smart charger
available to plug in whenever you had AC
available, and if it would run on a "modified
sine" inverter the additional cost over the
charger would be small. That would let your
starting battery get along in starting-battery
mode which is perfectly satisfactory for starting
and has been for the last century or so. The
potential would again exist of needing extra
cooling on the alternator to keep it from frying.
Yours,
d
