Re: lead-acid battery open circuit voltage

Uncle Al wrote:
> 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?

UA - Do I detect a mearest hint of sarcasm? ;-)
It's well know that *car* batteries deep-cycled will soon fail (50-100
cycles would not be far out)
Proper deep-cycle batteries do exactly what they say on the pack, and they
will cause a big dip in one's bank balance!
Also the source country can have a marked effect on life - there a lot
coming out of the Far East thesedays.

--
--
Ron Jones

Don't repeat history, see unreported near misses in chemical lab/plant
at http://www.crhf.org.uk
"The most exciting phrase to hear in science, the one that heralds new
discoveries, is not 'Eureka!' (I found it!) but 'That's funny ...'" :
Isaac Asimov:


.

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