You guys are really getting into this battery thing.
One thing you need to consider.
1) You need to charge your battery fully before a hard trip or hard use
with a regular battery charger because it can take as much as 72 hours to
fully charge a battery. If you have some kind of trickle charger that you
connect nightly it will do the same; fully charge your battery. Checking
the battery with a hydrometer is the proper way, 1260 specific gravity if
I remember right.
Automobile charging circuits seldom fully charge a battery, too many
variables in load, it fools the regulator.
This isn't Friday crap.

Stan Wilder

On Fri, 11 Oct 2002 23:28:32 -0400 David Beierl <dbeierl@ATTGLOBAL.NET>
writes:
> At 11:04 PM 10/11/2002, Larry Chase wrote:
> >I'm getting ready to do some Battery requirement calculations.
> >
> >Assuming a OPTIMA D750 Yellow Top Deep Cycle Battery
> >
> >Rated at 120 minutes of Reserve Capacity at a 25 Amp draw.
> >
> >Specifications.
> >
> >Reserve Capacity - Minutes: 124
> >Capacity (C/2 rate) - Amp Hours: 52
> >Capacity (C20 rate) - Amp Hours: 65
> >
> >Am I correct in assuming that a 10 Amp Per Hour Power requirement
> >would mean this battery would last 5 hours before needing a
> recharge?
>
> Ten amps draw for one hour equals ten amp-hours, so five hours would
> be
> fifty amp-hours.   That part's easy.  Now comes the fun stuff.
>
> First thing is that your alternator with the installed regulator
> will never
> bring the battery to full charge.  For thorough discussion of this
> visit
> http://www.amplepower.com/ and read through the discussions of
> charging
> available there (not always under completely obvious headings).  For
> your
> reference, the stock regulator has a fixed setpoint of (I believe)
> 14.1
> volts, measured inside the alternator and not at the battery.
>
> Second, a rule of thumb for most economical overall operation
> (taking into
> account battery life, initial cost and charging cost, but not
> necessarily
> the cost of hauling the weight around) is to assume that only 35% of
> the
> nominal capacity of the battery will be used.  This depends on two
> factors:
> the first is that putting the last 15% of charge into a battery
> takes
> hours, even assuming that the regulator will do it at all.  Second,
> the
> lifetime (in charge-discharge cycles) of a lead-acid battery is
> greatly
> increased (factor up to five) by not discharging it below 50%.
> Hence 85%
> max - 50% min = 35%.  In that case you might only be able to draw
> ten amps
> for a bit over two hours.
>
> However, you may well decide to discharge farther than that, down to
> a
> minimum of maybe 80%.  That would give you a usable capacity of [up
> to] 65%
> of nominal, at the expense of having many fewer charge/discharge
> cycles
> (for argument, say 200 instead of 1000).  Doing it that way, you
> might be
> able to run ten amps for about 3 1/2 hours.
>
> Note that the Reserve Capacity rating assumes a fully charged
> battery
> (unlikely without external charging or enough fancy hardware that
> you'll
> already know the answers to this question) under ideal conditions
> (unlikely), to a point where damage to the battery may be likely.
> It's a
> useful *relative* measurement in terms of how long you could nurse a
> car
> along the road drawing 25 amps after it quits charging.  In fact 25
> amps is
> probably more current than it's wise to draw from a battery this
> size at
> all (again, for best battery longevity).  The typical rule of thumb
> is C/4
> for conventional batteries, and maybe up to C/3 for gel and AGM
> (like the
> Optima) batteries.
>
> david
>
>
> --
> David Beierl - Providence, RI
>   http://pws.prserv.net/synergy/Vanagon/
> '84 Westy "Dutiful Passage"
> '85 GL "Poor Relation"
>
>

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