DC Supply! Monthly Electrical Ezine

CBC Design (tm) - January 2002 Issue. ISSN 1475-3464
Email: cbc_design@btconnect.com

"...Maintaining a reliable DC supply."



- Editorial
Solar Power Cells. (Article)
Voltage Monitoring. (Article)
- Competition - Win FREE battery pack!.
- Readers Questions
- Subscriber Ads



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! 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 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.

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.


*** NEW! 12 and 24V DC 60 Watt lamp dimmers ***

Dims single or multiple lamp assemblies with a maximum rating of 60 watts!
Lamps can be adjusted from a dim glow to bright light!
Regular use reduces battery power consumption and increase lamp life!
Fitted with RFI Suppression!

Go to http://www.cbcdesign.co.uk/dimmer.html and take a look at the
product in more detail! ______________________________________________________________________

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
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!


*** NEW! 12 and 24V DC Low Battery Alarm ***
Protect your vehicle batteries from deep discharge with a low battery alarm.
Easy to Fit, Easy to Use and inexpensive to boot!
Designed to protect batteries in cars, trucks, boats and mobile homes!
Built in warning sounder!
Goto http://www.cbcdesign.co.uk/battalarm.html and download a data sheet or
order your alarm NOW!


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Questions from Graham PickeringWhat 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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