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EDITORIAL.
Welcome to our October
issue.
Our
apologies for the late publication of this months
issue.
This month we take
another look at cell maintenance during the
winter
months
concentrating on physical and electrical
parameters formulated to get the
best
possible performance from our cells
next year.
Our
second article looks at cell leakage. A typical lead acid
battery has a
specific
leakage factor that determines how fast the battery capacity
decays.
This
allows storage time and trickle charging current values to be
accurately
determined which is an important
consideration.
Thank you for
continuing to subscribe to our
publication.
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: Over
Wintering Cells Revisited: Alan Fidler.
Time to look at over wintering
our batteries again.
Batteries installed in automobiles or
appliances that won't be used
at least once per month, they should be
removed and stored in a cool dry
location, preferably in an ambient
temperature of 15 - 20oC.
Clean the battery terminals and remove all
traces of corrosion that may have
built up during the summer. Apply a liberal
quantity of anti-corrosive jelly
to each terminal, making sure that the lead
contacts are completely covered.
Wet lead acid cells may need to be topped up
as per the manufacturers
instructions using distilled or
de-mineralised water. NEVER use tap or
rain water as it contains impurities that
lower the internal resistance
of the battery. Many people don't realise
that in it's purest form, water is
an
insulator with a very high ohmic value.
The battery should be recharged at least
once a month using a voltage
controlled charging system. A quality
battery management charging system
automatically reduces the
output from a bulk mode to a trickle charge as
the
battery charges. Chargers of this nature can be left
permanently connected
without
damaging the battery.
Inexpensive transformer/rectifier based
chargers can be used to recharge
your cells on a month by month basis but you
must make sure the
battery isn't over charged. In fact, its now
possible to convert the cheap
and cheerful charger into an automatic
voltage controlled system by fitting
a suitable charge controller between the
charger output and battery.
Permanently installed batteries should be
recharged at least once a month
using a
suitable external charger or on board alternator. The battery
should
be recharged until the voltage reaches 2.3
volts per cell, about 13.8VDC on
a 12 volt installation. Using an on board
alternator, the output current will
gradually drop as the
battery voltage rises and once the charging
current
is approx equal to the battery capacity
divided by 600, the battery is charged.
TESTING YOUR
BATTERIES
If you have any doubts about the performance
of your batteries, they can be
tested. For a traction battery, connect a
load that simulates the discharge
current drawn during an engine crank. Your
battery manufacturer will be able
to tell you how long to leave the load
connected for and what the minimum
battery voltage should be at a given
temperature during and after the test.
Leisure batteries can be tested in a similar
manner. You simply apply a load
with a rating of 1/10th of the battery
capacity and record the time taken to
discharge the battery to 1.75 volts per
cell. If the battery performs as per the
manufacturers specification they can be
returned to service.
In either case, if your batteries don';t
pass the discharge tests, replace them
as soon as possible. In many applications
the batteries are an essential part
of the system and should be treated
accordingly.
Remember: Look after your batteries and
your batteries will look after you!
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______________________________________________________________________
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ARTICLE: Cell
Leakage. Author: Alan Fidler.
All
batteries leak. It doesn't matter if they are lead acid, Nicad or
any other type, they
will all
slowly decay due to inherent leakage within the battery. Left in
really poor
conditions they leak both electrically and
physically in some situations and this is
the
stage when dangerous chemicals emerge.
Electrical cell leakage is caused by a very
gradual reduction of the chemical reaction
which
generates free electrons. Take a look at last months article on cell
operation for
an
explanation of cell function. Anyway, as I was saying, the battery
gradually decays
by a
specific amount over time. Of course it generally takes 4-5 weeks
for this to happen
by any meaningful amount which is
why stored batteries are normally recharged once
a month
to overcome this self discharge characteristic.
Battery
management charging systems maintain the battery at the recommended
float
voltage
of 2.25 volts per cell at 20oC so self discharge is totally
eliminated but this
is not
necessarily the case with all so called automatic chargers. There
are a number
of
manufacturers who produce systems that switch off when the battery
reaches the
fully
charged voltage. Systems of this nature are not entirely successful
in overcoming
self
discharge in stand by applications and are more suited to cyclic
modes of operation.
Most
battery manufacturers specify the discharge characteristics of their
products so
it is a
fairly straight forward process to access trickle charging
requirements. It can be
estimated at Total battery Amphour rating
divided by 600.
As well
as electrical leakage, wet lead acid batteries have a habit of
becoming slightly
damp due
to vented gas produced during the charging cycle. It is important
that the
battery
case is kept as clean and dry as possible to prevent excessive self
discharge.
It is an
unfortunate fact that the moisture which accumulates on batteries of
this type
is often
mildly conductive which results in excessive self discharge
current.
Sadly,
batteries sometimes split and the evidence is clearly visible either
as liquid
electrolyte or corrosion where is should
not be. Once a battery is damaged this
severely, it is dangerously damaged and
must be discarded in accordance with
the
local tipping regulations for your area. It goes without saying that
batteries
must be
disposed of safely for both our sakes and the
environment.
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______________________________________________________________________
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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 Donald Hicks!
Question 1.
Why does aH
mean?
aH means
Amphour. It is an expression of battery
capacity.
Question 2.
Can
batteries be used upside down?.
Sealed
lead acid and sealed nicad batteries can be
used in
any orientation. It depends entirely on the
electrolyte
used in
the construction. A liquid electrolyte cell must be
kept
upright
at all times.
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