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EDITORIAL.
Welcome to
our September issue.
We have
had lots of new subscribers since our last issue and we would like
to welcome
each of
you to our publication. You can read previous issues by visiting our
website at
Its
almost a year now since we looked at battery maintenance with a view
to successfully
over
wintering our batteries. As the Winter months approach, we need to
inspect our
batteries and make sure that basic
maintenance procedures are applied.
For
those of you with an interest in the technical aspects of batteries,
our second article
looks at
the operating principle behind the lead acid battery. We explain in
layman's terms
just how
an enclosed box of lead and sulphuric acid produces electrical
energy.
Incidently, please feel free to submit
ideas for future articles you wish to see published or indeed, whole
articles if you wish too.
We hope you enjoy
this months issue.
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Editor: Alan Fidler.
Alan is the owner and manager of CBC
Design, a leading battery management company
based in the UK. He has worked in the
industry for over twenty years and has designed
charging equipment and battery monitors for some of the world
largest companies.
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ARTICLE: Basic
Cell Maintenance: Alan Fidler.
As the
colder months approach, we need to make sure our batteries are able
to
survive
the winter. This encompasses a number of factors including cleaning,
topping
up the
electrolyte and charging the cells at an appropriate
potential.
Most
lead acid batteries require an occasional clean. Corrosion builds up
over time
and the
vents fitted to each cell plug invariably end up clogged due to
moisture
and
dirt. Start by removing any corrosion around the battery terminals
and from
the top
of the battery. Using a damp cloth, clean the sides and base of the
battery
to
remove any spilt electrolyte, dust, dirt and
grease.
Now that
the battery housing is clean, remove each of the vent plugs and
check the
electrolyte level inside each cell. Top
them up in accordance with the manufacturers
recommended level, approximately 10mm above
the lead plates. Make sure the vent
holes in
each cell plug are free and clear by holding them up to the light.
Remove any
accumulated grime using a
cloth. Fit the vent plugs to each cell before
proceeding.
The
battery terminals should be covered in an anti-corrosive jelly
to prevent termination
failure.
You can use Vaseline however we recommend using a chemical
specifically
designed for the job. Here in the
UK, we use a product called "No Crode"
manufactured
by Holts. This particular products
destroys small particles of corrosive waste that
may
be
present thus eliminating any possibility of
failure. A similar product is available
from
most
automotive spares outlets throughout the world.
Now that
the batteries are clean, topped up and free from corrosion, they can
be charged
on a
monthly basis until the spring or maintained permanently by an
automatic battery
management charging system with a trickle
charged output.
To be
absolutely sure the batteries are in tip-top condition, it is worth
applying a load
to them
rated at 1/10th f the battery capacity. As long as on-load voltage
is above 10VDC
after
9.5 hours or so at 20oC, the battery is healthy. Of course it
must be fully charged
before
the load test is applied.
Remember: Look after your batteries and
your batteries will look after you!
______________________________________________________________________
______________________________________________________________________
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ARTICLE: Cell
Operating Principle. Author: Alan Fidler.
Batteries have been around for over two
hundred years. Modern batteries are many
times
more efficient than batteries produced even 30 years ago but in
principle, they
work in
exactly the same manner as the original did.
The
battery was invented by Alessandro Volta way back at the beginning
of the
nineteenth century. He created the first
battery using alternating layers of zinc,
paper
soaked in salt and silver. Known as a voltaic pile, the number of
alternating
layers
could be selected in order to generate a specific voltage and
current flow
occurred
whenever a wire was attached between the two ends of the
pile.
To this
day, batteries are manufactured in accordance with the basic design
principles discovered by this enterprising
individual although the combinations
have
been refined to produce the high energy cells we have
now.
The
simplest example of battery function can be demonstrated using
just three
items. A
zinc rod, a carbon rod and a jar of sulphuric acid. If the zinc
rod is
immersed
in the sulphuric acid, it will begin to dissolve. The rod will lose
two
electrons which combine with hydrogen ions
in the acid and create hydrogen
gas.
The
carbon rod is unaffected by sulphuric acid however, when connected
through
a wire
and load to the zinc rod, it allows the free electrons in the acid
to flow through
the wire
thus creating an electrical circuit. Indeed, close observation will
reveal the
release
of hydrogen gas around the carbon rod as current flows through the
circuit.
In this
example, a chemical reaction between the acid and zinc results
in free electrons.
By
combining different materials, the voltage generated by chemical
reaction can be
precisely determined. This is demonstrated
by the differing terminal voltages between
say a
lead acid cell and a Nicad battery. The lead acid cell produces
a voltage of around
2V per
cell against the nicads 1.4 volts per cell. a typical car battery
has 6 series
connected lead acid cells to generate a
nominal 12VDC.
Unlike
zinc carbon batteries, the lead acid cell has been constructed using
materials
that
allow the reaction to be reversed. The zinc carbon battery decays as
the zinc rod
dissolves and the sulphuric acid weakens.
Once discharged, the zinc carbon cell is
dead and
cannot be re-used. The lead acid battery however is a different
animal
altogether.
A
typical 12V car battery is manufactured using a stack of alternating
lead and lead
dioxide
plates. Immersed in sulphuric acid, a chemical
reaction occurs which
results
in an
electro motive force otherwise known as voltage. Unlike the zinc
carbon cell, the
plates
in your car battery do not dissolve, instead a layer of lead
sulphate builds up
on the
plates whilst the acid becomes progressively weaker. By reversing
current flow
through
the battery, lead and lead dioxide are reformed thus recharging the
cell.
This is
rather simplistic explanation of cell operation. Those of you with a
comprehensive
understanding of chemistry and physics, the
following Hawker Energy site will give you a
more
detailed explanation:-
In
theory, a lead acid battery can be charged and discharged hundreds
of times as
long as
the conditions within which the cells operate are precisely
controlled. It is
therefore vital that proper charging
techniques are utilised to get the best
performance
from
them. Over charging a lead acid battery damages the internal plates
resulting
in cell
failure. Over discharging the battery can result in an excessive
build up of lead
sulphate
otherwise know as sulphation which is more often that not partially
irreversible.
______________________________________________________________________
______________________________________________________________________
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______________________________________________________________________
COMPETITION:
Subscribe to our ezine and you
will be automatically entered into our competition where you can win
a FREE Nicad "AA" battery pack.
Simply send your email
address (No free email) to cbc_design@btconnect.com with the words
"SUBSCRIBE" in the
subject line.
______________________________________________________________________
READERS QUESTIONS.
Questions from Sean
Malveny!
Question 1.
Why are battery terminals made of copper instead of
lead?
Ideally, battery terminals would be made of lead
to limit corrosion
but unfortunately, lead is too soft to use
as a termination.
Question 2.
What
causes corrosion?.
Corrosion is a by-product of conduction
through dissimilar metals. A
small
potential difference between the battery terminals and
connected
conductors is largely
responsible.
______________________________________________________________________
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