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EDITORIAL.
Welcome to our first publication of
2002.
We
hope you had a good Christmas and a happy new year and would like
to
welcome new subscribers who have recently
joined us.
This month we continue looking at ways of
generating DC power from another free
energy
source, the sun. Whilst solar panels are not the most
efficient component
available, in sufficient numbers a
considerable amount of electrical energy can be
generated if enough cells are linked
together. We'll show you how to get the best
performance from a typical solar
panel.
One of
the most overlooked aspects of any installation is the ability to
see what the
system
is doing as a whole. Without appropriate monitoring, the
installation could
be
working perfectly or on the verge of catastrophic failure. Some
form of continuous
measurement is required for reliable
operation and voltage or current monitors are
an ideal
way of solving this problem.
We hope
you enjoy reading this months issue and wish
you a prosperous new
year!
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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 seventeen years and has designed charging
equipment and battery monitors for some of the world largest
companies.
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ARTICLE: Solar Power Cells. Author: Alan Fidler.
Solar
panels can be an effective way of generating FREE power from the
most dependable
energy
source, the sun. In some areas of the world where the sun shines
almost
daily,
solar can be the main contributor to power
generation.
Unfortunately, solar panels are extremely
inefficient converting less that 10% of the
suns
energy into useable electrical power although recent
developments have increased
this
figure to approximately 16%. Even so, this still leaves a whopping
84% of untapped
solar
power and it is for this reason that panels tend to be rather
large.
Hopefully, there will be further
developments in solar technology that will enable
some
of the
wasted heat to be converted into electricity. Peltier pump devices
convert electricity
to heat
so it may be possible to reverse this
function, combine the two elements and greatly
increase
the energy output of a typical solar panel. Time will
tell.
A
typical 12V 500mA (0.5A) panel measures 360mm x 285mm x 17mm and
weight
around
700 grams. They can be wired in series to increase the output
voltage or
parallel
to increase the output current. A typical installation would consist
of a series
parallel
configuration designed to harness as much energy as required.
Panels vary in price from approx
$80.00 for a 12W panel up to $700.00 for a 120W
panel
but
since many have a life expectancy of over 25 years they can,
over time not only recoup
the
initial purchase price but save money too.
Installation methods vary from rooftop
layouts to ground based motorised assemblies.
The best
systems incorporate solar tracking technology that moves the panel
throughout
the day
so it harness as much power as possible. Solar panels work best when
pointing
directly
at the sun and solar tracking devices make sure the panel is always
in direct
alignment with it for maximum
efficiency.
If you
are interested in generating your own electrical supplies and you
live in an area
where
the sun shines regularly, solar panels may be an ideal solution.
Demand for
solar
energy in California is now at an all time high. Clearly, solar is a
valuable energy
source
and best of all, it's FREE. As the demand for panels increases,
prices will fall
and
eventually, we may all be able to generate our own supplies
relatively cheaply.
Contact
your local wind and sun energy store and discuss your solar
requirements
with an
expert. Many suppliers have a wealth of experience from which they
can
draw
upon to design the perfect system for your individual needs, making
sure you
get the
best performance from the outset.
Solar
panels are not cheap so don't be tempted to buy the first unit
you see.
Take
your time, research the subject in full, talk to as many
experts and end users
as
possible and you should be able to construct a near perfect
system.
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______________________________________________________________________
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ARTICLE: Voltage Monitoring. Author: Alan
Fidler.
Maintaining
a reliable DC supply in unattended applications can
be almost impossible
unless monitoring
the system as a whole from a remote location
can be achieved.
Fortunately, there are a number of
manufacturers who produce a variety of voltage
and
current monitors that make the above quite straight
forward.
Lead
Acid batteries need to be maintained within a given
voltage band of around
1.75-2.25 volts per cell from
fully discharged to a fully charged state.
Clearly,
it is imperative that the batteries are
inspected regularly either locally or
remotely to make sure they are neither
under-charged, over-charged or left in a
discharged condition for any length of
time.
Voltage
monitors are the best way to measure the battery since they can
be
configured as High Voltage or Low Voltage
monitors or a combination of the two.
A High
Volts Monitor will alarm should the battery voltage rise above a
maximum
limit
whilst a Low Volts Monitor makes sure the
batteries are not over discharged.
Low
voltage monitors can also be used to disconnect loads from the
batteries to
protect
the cells from deep discharge.
Many
industrial grade monitors include two pole changeover relay contacts
for
remote
indication via telemetry, fault detection to relay de-energisation
delays
to avoid
false signals during an engine crank for example, and local led
healthy
and
failure indicators.
Current
monitors are generally used to measure the performance of the
charger
assembly. In all charging conditions,
including trickle, a small amount of current
should
be delivered to the battery to compensate for self discharge. A
current monitor
alarms
if the current flow drops below a pre-determined minimum and
indicates a
charge
failure condition.
As well
as charge failure, current monitors are also ideal where critical
equipment
needs to
be permanently energised. The monitor measures the current flow
to
the
critical appliance and alarms if it drops below a safe
level.
Earth
leakage monitors do exactly what there name suggests. They alarm if
current
flows
from either pole of the DC installation to earth, an important
element of design
in many
industrial and marine applications. They normally include a volt
free relay
for
remote signals and status led indicators.
Less
complicated alarms are available for semi attended applications
on
vehicles
or boats. High or Low Battery alarms can monitor the battery and
if the
voltage rises above or falls below a safe limit and sound
an on-board siren or
buzzer.
Regardless of price and sophistication,
most voltage & current monitors are fully
adjustable to allow the user to compensate
for volts drops in cables or semi
conductors such as diodes
installed in series with the loads.
One
final point: Which ever monitor you use, make sure it is fitted
properly.
The
number of installations I have visited over the last
ten years or so that failed
as a
result of a total lack of monitoring is high. I have
even visited a site where
monitors
were included with a charging system but never
wired to remote annunciators
so the
initial failure was never detected and the result was
destroyed batteries. Unwired
alarms
are a waste of money, time and power. Fit them
properly or not at all.
Sadly,
many of us must seem destined to learn the hard way and will end up
writing off
batteries that could have easily been
protected for an extra ten or twenty dollars. To use
an old
analogy, nobody builds a stable without
doors since the consequences are obvious.
Similarly, it is not
cost effective to install batteries
costing anything from tens to hundreds
of
dollars only to end up replacing them a year or two
early because we cut corners.
Voltage
and/or current monitors give us peace of mind and
can extend the life of an
installation considerably.
Remember: Look after your batteries and
your batteries will look after you!
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CLASSIFIED ADS:
*** NEW! 12 and 24V DC Low Battery
Alarm ***
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deep discharge with a low battery alarm.
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and inexpensive to
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and mobile homes!
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order your alarm NOW!
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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 Graham Pickering! What does "C/10" mean?
Battery capacities, i.e. how much energy
they contain is expressed
as
an amp hour rating. C/10 is the capacity of the battery in a 10
hour
period. A 100AH battery has a C/10
rating of approx 8A.
Question 2! How should a battery be sized for a given application?
A
given discharge current can be drawn from a battery to a
specified
end of discharge voltage. If a 10A load was
required within a given
voltage range of 21-27 volts DC, a battery
with a 100A rating down
to 1.75 Volts per cell will be required. In
practice an allowance of
20% is given for self discharge and
temperature variations so a 120AH
battery would be the minimum
size
required.
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