Re: lead-acid battery open circuit voltage

Ron Jones wrote:
>
> dmartin@xxxxxxxxxxx wrote:
> > I've looked and looked for real data about how fully charged Open
> > Circuit Voltage changes with age or cycles for a lead acid battery.
> >
> > The open circuit voltage I'm refering to is the voltage that you
> > measure at 77-78F for a fully charged lead-acid battery that has
> > rested for a while (actually the voltage you get if you extrapolate
> > to zero current.)
> >
> > Differing OCVs can cause trouble when batteries are placed in
> > parallel. Say that two fully charged 12V batteries have OCVs that
> > differ by 0.1 volt. Maybe one has lead-antimony plates and the other
> > lead-calcium plates.
> >
> > Now we hook these two batteries in parallel. Current will flow from
> > the higher voltage battery to the lower voltage one until both
> > voltages are equal; ie. 0.1 volt will be lost from the higher OCV
> > battery.
> >
> > This is bad because that 0.1V probably represents more than 10% of
> > that battery's total charge.
> >
> > I'm guessing that sulphation effects increase a battery's internal
> > resistance but should have little direct effect on its OCV at full
> > charge.
> >
> > It is hard to see how OCV would change with a battery's age unless the
> > plate composition changes with age. This is entirely possible. I just
> > don't know what happens in real life.
> >
> > Dave
>
> Toooo many variables.... Battery charge and discharge is almost a subject
> in it's own right. Obviously best to use identical batteries when in
> parallel.
> This is a useful link www.batteryfaq.org
> Remember every discharge of a battery shortens it's life! Plus discharge
> more than about 15-25% (car battery); 40-50% (leisure battery); 70-80% (deep
> cycle) and you are doing irreversible damage. Questions on charging /
> discharging batteries come up at regular intervals on boat / caravan groups
> (I know at least 1-2 times a year on uk.rec.waterways)

Good Lord! Do you mean to say that the E*L*E*C*T*R*I*C car with its
deep discharge cycling of trays of cheap Detroit car batteries was
a... a... a (whisper it softly) SHAM! That loss of 50% or more
mileage capacity in 6 months of use wasn't a coincidence across all
the hardware?

--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
.

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