has "been brought up" to 13.2 Volts, it only means that the charger can
sustain
that Voltage. Immediately after removing the charger, the Voltage will still
be
artificially high.

"Fully charged" is not "artificially high."

Do you dispute that the voltage of a battery
cell is 2.2 volts? Yes or no answer please.

Do you dispute that 6 x 2.2 = 13.2?
Yes or no answer please.

After the battery self discharges a bit, it will stabilize about 12.6 or so.
But it has
self discharged to get to that level, and while it may be "adequately" charged
or even "typically" charged, a battery cell is not fully charged until it gets
to 2.2 volts.

Nigel Calder not whithstanding.

It's basic physics.

"Gould 0738" wrote in message
...
has "been brought up" to 13.2 Volts, it only means that the charger can
sustain
that Voltage. Immediately after removing the charger, the Voltage will still
be
artificially high.

"Fully charged" is not "artificially high."

Do you dispute that the voltage of a battery
cell is 2.2 volts? Yes or no answer please.

Sure, I'll dispute it. While the voltage of an ideal cell might be higher, the
"open circuit voltage" of a modern marine battery such as a Rolls (like you
have) or a Trojan (like I have) will be somewhat lower, perhaps 2.13 volts or a
tad less. If you have any doubt, you can look at the Rolls site or the Trojan
site.
http://www.rollsbattery.com/Bulletins/600.htm
http://www.trojanbattery.com/custome...erymaint4.html

Of course, to properly measure this, you have to wait a little while (at least
10 minutes, better after an hour or more) for the battery to stabilize
internally.

Now you can probably find 1000 sites oriented towards high school chemistry and
physics labs that say 2.2 volts, but I claim they are all trumped by the people
that build and maintain actual marine batteries, which are, after all, a
slightly different formulation than the traditional lead acid battery.



Do you dispute that 6 x 2.2 = 13.2?
Yes or no answer please.

Duh. Garbage In Garbage Out. You're really trying hard to be a horse's ass
here, aren't you?



After the battery self discharges a bit, it will stabilize about 12.6 or so.

It isn't self discharge. If you read the quote from Calder you would understand
that. The battery charger can induce a "surface charge" that is not
representative of the actual state of charge.



But it has
self discharged to get to that level, and while it may be "adequately" charged
or even "typically" charged, a battery cell is not fully charged until it gets
to 2.2 volts.

Actually, that's not the issue at all. The issue is that the cell can read 2.2
volts and NOT be fully charged. Any battery that has been charging for a while,
regardless of what state of charge it has reached, might read 13.2 volts
immediately after removing the charger. That's why its meaningless.

Are you claiming that if you can ever read 13.2 volts from a battery it must be
fully charged?
Yes or no answer please.



Nigel Calder not whithstanding.

Yes, we know that the opinion of experts and all of the other observers is not
good for your argument.



It's basic physics.

No. Its marine batteries. Sometimes real life is a bit different from what you
read in a high school textbook.

Are you claiming that if you can ever read 13.2 volts from a battery it must
be
fully charged?
Yes or no answer please.

Must be?
No. You could get a false reading.

But you can get a 13.2 reading from a fully charged battery without it being a
false or artificial reading. That's the combined voltage of all six cells
before the battery self discharges to a lower voltage.

After a battery partially discharges, it will stabilize around 12.6. Partially
discharged is not the same as fully charged- although it will represent a
common state of charge for batteries that have been removed from
a float charer and allowed to self-discharge to that level.

Why do you suppose every battery charger mfg sets float voltage at 13.2 or
13.3?
Just an arbitrary number?

I'm amused to see that the laws of physics are suddenly suspended when they
don't support your tottering argument. :-)

"Gould 0738" wrote in message
...
Are you claiming that if you can ever read 13.2 volts from a battery it must
be
fully charged?
Yes or no answer please.

Must be?
No. You could get a false reading.

Exactly. You have no information. The battery could be at 60% or it might be
at 100%. You have to wait until the voltage stabilizes.



But you can get a 13.2 reading from a fully charged battery without it being a
false or artificial reading. That's the combined voltage of all six cells
before the battery self discharges to a lower voltage.

It isn't "self discharge."


After a battery partially discharges, it will stabilize around 12.6.
Partially
discharged is not the same as fully charged- although it will represent a
common state of charge for batteries that have been removed from
a float charer and allowed to self-discharge to that level.

Since this happens fairly quickly, are you now claiming that battery will loose
a sustantial part of its charge in the the first 10 minutes? It was at 100%
then it drops to what, 80% ten minutes later? Then magically it goes into a
mode where it only looses 5% a week? What color is the sky in your world?



Why do you suppose every battery charger mfg sets float voltage at 13.2 or
13.3?
Just an arbitrary number?

What does this have to do with anything?



I'm amused to see that the laws of physics are suddenly suspended when they
don't support your tottering argument. :-)

Tottering? You just admitted I was was right! Your words: "You could get a
false reading." You originally claimed that 13.2 meant the battery was fully
charged. Now you admit it could be a false reading. Your right. The only way
to tell what the true state of charge is to wait for the voltage to stabilise
(not self-discharge). If it stabilises at 12.6, its fully charged.

On 24 May 2004 00:15:23 GMT, (Gould 0738) wrote:

Are you claiming that if you can ever read 13.2 volts from a battery it must
be
fully charged?
Yes or no answer please.

Must be?
No. You could get a false reading.

But you can get a 13.2 reading from a fully charged battery without it being a
false or artificial reading. That's the combined voltage of all six cells
before the battery self discharges to a lower voltage.

After a battery partially discharges, it will stabilize around 12.6. Partially
discharged is not the same as fully charged- although it will represent a
common state of charge for batteries that have been removed from
a float charer and allowed to self-discharge to that level.

Why do you suppose every battery charger mfg sets float voltage at 13.2 or
13.3?
Just an arbitrary number?

I'm amused to see that the laws of physics are suddenly suspended when they
don't support your tottering argument. :-)

If you want to talk laws of physics, you're all wrong. Sure, you can
find web sites that support just about any voltage of a lead acid cell
from about 2 volts to 2.2 volts with most of them supporting a claim of
around 2.1 to 2.15 volts. But if you want to talk physics, why not
write out the half-cell reactions that take place at the cathode and
anode of a lead-acid battery. Add them up and that is the potential of
the battery.

I'd write them here but the characters are hard to reproduce in ascii so
I'll just say that the anode reaction is about 0.36v and the cathode
reaction is 1.69v for a total of 2.05v. You can look them up yourself
by googling pbs04 half-cell reactions. Now, to see why 2.05v can really
be anything "around" there due to differences in the concentrations of
the chemicals as well as temperature, google the Nernst equation, which
tells you how the potential of the cell varies according to temperature
and concentration.

The Nernst equation also explains part of why a lead-acid cell will have
a higher voltage when it's just taken off a charger and then settle to a
full-charge voltage a little bit lower and still be considered to have a
100% charge. It has to do with 1) the concentrations of the chemicals
at the plates equalizing some time after removing the charging voltage
and 2) the cooling down after charging which lowers the potential. It
nothing to do with self discharge or internal resistance.

Steve

On Mon, 24 May 2004 02:34:50 GMT, (Steven
Shelikoff) wrote:
The Nernst equation also explains part of why a lead-acid cell will have
a higher voltage when it's just taken off a charger and then settle to a
full-charge voltage a little bit lower and still be considered to have a
100% charge. It has to do with 1) the concentrations of the chemicals
at the plates equalizing some time after removing the charging voltage
and 2) the cooling down after charging which lowers the potential. It
nothing to do with self discharge or internal resistance.

================================================== ==

Thank you. It's good to see a little high quality science interject
itself into an otherwise degenerating discussion. :-)

All the better it supports what most of us have observed. Chuck's
electrons have become damp, slugish, and not a little bit stubborn,
having lived in the Pacific North West for so long.

Thank you. It's good to see a little high quality science interject
itself into an otherwise degenerating discussion. :-)

All the better it supports what most of us have observed. Chuck's
electrons have become damp, slugish, and not a little bit stubborn,
having lived in the Pacific North West for so long.


Steve's hypothesis states that once the battery has achieved a full charge of
2.2 volts per cell, the decrease to 2.1
is due to an a change in the chemical concentration within the cell. Very
probable scenario.

Doesn't support any sort of position that the battery was never charged to
13.2, though, does it?

Merely explains with greater technical clarity than the term "self discharge"
why the voltage will eventually drop.

And that's the Pacific North WET, thank you very much. :-)

On 24 May 2004 06:11:19 GMT, (Gould 0738) wrote:

Thank you. It's good to see a little high quality science interject
itself into an otherwise degenerating discussion. :-)

All the better it supports what most of us have observed. Chuck's
electrons have become damp, slugish, and not a little bit stubborn,
having lived in the Pacific North West for so long.


Steve's hypothesis states that once the battery has achieved a full charge of
2.2 volts per cell, the decrease to 2.1
is due to an a change in the chemical concentration within the cell. Very
probable scenario.

Doesn't support any sort of position that the battery was never charged to
13.2, though, does it?

It may have been charged at 13.2, to 13.2, or whatever you want to call
it. But if you're taking the measurement right after charging, you're
reading an artificially high voltage. When the battery cools down and
the chemicals reach a constant concentration over the space inside the
battery, the voltage will drop to it's steady state full charge of well
less then 13.2 volts. The actual chemical voltage potential of the sum
of the half reactions of a lead-acid cell is between 2.05 and 2.06
volts.

The condition of a battery being fully charged is actually a chemical
condition and not a specific voltage. The battery is fully charged when
the negative plate is made fully of lead, the positive plate fully of
lead dioxide and there is no lead sulfate on either plate. The
electrolyte is sulfuric acid (around 25-35%) and the rest water. The
temperature and the concentration of the sulfuric acid can affect the
voltage of the fully charged battery. The maker of the battery will be
the one who knows what their designed full charge voltage is. They'll
also have to tell you how to measure it, i.e., what temperature, how
long to wait after charging, etc.

The voltage of the battery will drop as it discharges either through
self discharge or by being used because the electrolyte becomes diluted,
i.e., the concentration changes, when it breaks down into hydrogen and
sulfate and the hydrogen combines with oxygen to form more water. The
sulfate combines with the lead in both plates to form lead sulfate.

When the battery is fully discharged, both plates are covered in lead
sulfate and the electrolyte is almost all water. You don't want your
battery to get in that condition.

Merely explains with greater technical clarity than the term "self discharge"
why the voltage will eventually drop.

The voltage will drop eventually due to self discharge. But that's
something different then what happens in the few hours after removing
the charging voltage. The self discharge rate of lead acid batteries is
very variable. Sealed lead acid batteries lose maybe 3% of their
capacity per month. That also depends on temperature and the rate can
double if you increase the temp by like 20 degrees F.

However, you won't notice any self discharge in the few hours it takes
for the voltage to settle down after you remove the charger. I.e., if
the battery is fully charged and the float charger was at 13.2 volts and
you remove it and immediately measure the voltage as 13.2 volts, the
battery will still be fully charged (virtually no lead sulfate on the
plates and the same concentration of sulfuric acid in the electrolyte) a
few hours later when the voltage settles to a lower value.

Steve