"Meindert Sprang" wrote in message
...
snip
There are two possible scenarios: one battery wears more quickly than the
other, eventually reaching a state where the cell voltages reach higher
values due to increasing internal resistance. Thus the charges shuts off
too
early, leaving the better battery not topped up.
The charger does not monitor cell voltages. It monitors the voltage across
all the cells in series. I don't know what you mean by 'wears', but the
initial charge state of individual cells does not affect the voltage level
at which the charger shuts off.
The other possibility is that due to a deeper discharge of one battery, it
takes longer for the total voltage to reach the point where the charger
goes
from bulk to float. So while for the more empty battery the charge is
still
ok (bulk), the other one still gets the full bulk current too while it
should receive a float charge.
Deeper discharge of some cells in the string will not, of itself, mean that
the charge takes longer. The _difference_ doesn't matter. The amount of
charge required controls the charge time. Whether OP is running his radio
off one battery or both makes no difference to the ah used, and therfore no
difference to the charge time (except, of course, that if he uses a
converter he will be consuming more ah for a given usage than if he uses
just one battery).
Have you ever disassembled a broken battery pack of some device? In 99%
of
the cases you will find all cells in perfect condition (charged and
all)
except one, which was obviously the weakest in the chain, showing a
reversed
voltage.
You have demolished our own argument. All cells were treated
identically,
yet one has collapsed! You can't use that evidence to support a claim
that
cells treated differently are more liable to collapse (which I assume is
what you are trying to say).
There is always one cell that collapses first (the weakesrt), due to
tolerances in materials, production, etc. By introducing an extra load
(wear) on part of the cells in a string, they are more likely to collapse
first.
It's not the extra load that causes cell collapse. Mistreatment of the
batteries (either, or both) will shorten their life. If they are operated as
they are designed to be operated then manufacturing differences between
cells are more significant than the fact that some cells have been
discharged to a lower level than others. If you do a proper study of those
dissambled batteries you will find that the collapsed cell is not random -
it has a strong bias towards the poitive terminal.
Collapse of one cell is the most common mode of failure for wet cell
batteries, but it is not associated with differential discharge rates.
We all know that a lead-acid battery suffers from deep discharge.
Who is talking about deep discharge?
And in
this setup, it is a plain fact that the battery "below" the tap is
discharged sooner then the one "above" the tap. And if the charger is on
"the outside" terminals, it can only see the charge state of the entire
string, which is in this case, wrong information.
It is not "discharged sooner". It is discharged to a level slightly below
the other. The charge state of the 'entire string' is not 'wrong'
information. It will indicate the amout of charge required, and any
differential between individual cells, or sets of cells, is not relevant.
For years battery manuafacturers have provided a 12v tap across the first
eight cells of high voltage industrial batteries. There has never been
any
evidence that using the tap shortens the battery life, and it has never
been
the experience of the users.
Uhm, 12V across 8 cells? You are talking about non-rechargable batteries
here?
No. I am talking about standard industrial lead acid wet cells, so I guess
the number is 10. If you need to know it exactly you can take yourself down
to any nearby warehouse and look at the batteries used in a forklift battery
system, and count the number of cells set aside for the 12v tap.
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