Welcome to our February edition of DC
Battery management is a
Getting the very best performance from any
battery pack depends upon applying the
correct charging regime, limiting the
discharge to a safe level and making sure
batteries are operating a full capacity in
the working environment. This month, we look
the principles of battery management and how they should
be applied in the most
frequently asked how a battery charger can be built using simple
both inexpensive and reliable. In our second feature, we'll show you
how you can construct a quality charging system for small
lead-acid cells up to 60AH using thyristor
constant potential charging regime.
always, we welcome any comments you may have and hope you enjoy this
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 eighteen years and has designed
charging equipment and battery monitors for some of the world
ARTICLE: Battery Management. Author: Alan Fidler.
management is essential if an installation is to perform to the
specified in the original design. Failure
to properly maintain the cells will, at the very
cause problems and at worst, may lead to a loss of life. Imagine how
be if the battery used in a special care baby unit (Scbu)
first principle in battery care it to charge the cells at regular
intervals in accordance
battery manufacturers instructions. In some cases, this may involve
or the connection of a permanent constant potential system that
continuously. Visit the following page for a
demonstration of the three principal
charger has been selected, the next point to consider is the
installation. Lead-acid batteries should not be discharged
beyond 1.55 volts per cell
in any situation. In some cases 1.75
volts per cell is the minimum discharge voltage.
of limiting the end of discharge voltage may be
required using a low volts
disconnect circuit. Nicad batteries are
more tolerant to excessive discharge than lead acid cells are but
similar considerations should be applied for
third consideration is voltage and current monitoring as discussed
in last months issue.
imperative that the installation function within prescribed limits
for reliable operation
and systems in remote locations may
require signal telemetry or similar to warn end
potential problem has occurred. A number of alarms may be required
to achieve this,
Volts Monitor for over-charge warning, a Low Volts Monitor to
indicate that the battery
discharging or a Charge Failure Monitor to warn end users that the
batteries are off charge.
industrial battery charger manufacturers apply the basic
elements discussed above
to make sure the end customers dc supply is a reliable one.
efforts of these companies to create the perfect system, end users
the maintenance requirements laid down by the manufacturers
and wonder why
batteries fail 2 or 3 years before they should.
Batteries have a fixed life from several
years to over a decade. It is therefore
batteries are discharged at regular intervals to confirm that they
manufacturers specification. This is particularly important as the
tests would traditional be applied at a current level that is
similar to the normal
application in which the cells function.
Sadly, this obvious necessity is often ignored
is too late.
management then, encompasses the following
Selection of a battery with an appropriate voltage and current
Selection of an appropriate battery type, i.e. leisure or
Selection of an appropriate charging system to suit the battery and
Installation of appropriate discharge voltage limiting
5. Choosing appropriate voltage and
current monitors for early fault detection.
6. Battery discharge testing on a
regular basis to confirm battery performance.
manufacturers work hard to produce reliable cells. Battery
manufacturers take pride in building a
suitable charger. The rest is up to the
Remember: Look after your batteries and
your batteries will look after you!
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ARTICLE: Designing your own Charger. Author: Alan
your own battery charger may seem straight forward. After all, the
vehicle batteries consist of nothing more that a mains transformer,
a full wave bridge
rectifier and a simple moving coil ammeter
to indicate charging current.
CBC Design acknowledge the popularity of these cheap and cheerful
the business of battery management and chargers of this nature have
no place in
properly constructed system that can maintain the batteries
a charging system that can be used safely and permanently in some
more sophisticated system is required and this
is precisely what we want to help
heart of this type of battery charger is the mains
transformer. To calculate the
transformer rating we multiply the charging
current by 1.5 to derive an RMS rating.
be constructing a charger suitable for batteries up to 60AH so a 6A
require a transformer with a 9A rms rating. The transformer
be approx 17 volts for a 12V charger or 33 volts for a 24V model.
will be 110V or 230VAC depending upon your mains
need to select a suitable full wave bridge rectifier. Since the
charger has an
operating voltage of 12 or 24V, a 60V
rectifier rated at 10A will be adequate.
rectifier will need to be mounted to a metal surface so that it
stays cool when
delivering full current and because of its
mounting position must have an isolated base.
conducting element will be a Thyristor. We will require a 10A type
rating of 60VDC or above. Most thyristors of this rating are housed
in a transistor package called a TO220 can. Since the housing
includes a live metal base and tab, it
need to be mounted on a heat sink but isolated from it using a TO220
heasink will need to have a rating of at least 4oC per watt or
better to maintain
temperature of less than 24oC above ambient.
item we need is a suitable controller to switch the Thyristor.
They are generally
called series controllers and are
available from several companies for about £20.00
ratings of 5 or 10ADC at 12 or 24V.
transformer will have 4 connections, two primary (Live &
Neutral) and a secondary
of 0v & 17v or 0v & 33v depending upon the nominal charger
voltage of 12 or 24VDC.
the two secondary cable to the terminals marked AC or ~. There are
terminations, one for each secondary
connection. Make sure you use 10A rated cable
the transformer connections.
the primary connections to the incoming mains supply. One of the
connected to Neutral. The second should be connected to Live via a
fuse and switch. We
recommend fitting a fuse and rated
according to the following calculations:
Transformer secondary voltage multiplied by
the secondary current = VA1.
VA1 by the mains supply voltage and multiply by
results indicate the nearest type "T" fuse value
the live supply switch must be rated to withstand the input current
drawn by the
transformer and have a surge rating of at
least 10 times the fuse value due to transformer
when the mains supply is connected.
THYRISTOR & CONTROLLER
anode of the Thyristor must be connected via 10A cable to the
positive rectifier connection
the cathode is connected to charger output positive known as B+
using similar cable.
the controller negative terminal to rectifier
a 10A rated cable from rectifier negative to charger output
the controller battery positive cable to B+.
the controller supply to rectifier positive.
the grey controller cable to charger output negative known as
cable is connected to the Thyristor gate
check the connections with the manufacturer since they vary slightly
chargers incorporate a moving coil ammeter to indicate the charging
meter is series with the supply from the Thyristor output to the
battery positive supply
of meter to Thyristor) or between the battery negative terminal and
of meter to battery).
have a fully functional constant potential charger that can be used
acid batteries at 12 or 24V. Connect the positive charger output to
battery positive and the charger output negative to battery
negative. Switch on the mains supply to energise the
If you have any questions regarding the
controller, contact the manufacturer.
you enjoy building your own fully automatic battery charger and
enjoy many years
service from it.
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Questions from Stephanie Willis!
does CC and CP stand for?
stands for Constant Current, CP stands for Constant Potential. They
to charging methods applied to nicad (CC) or
lead-acid (CP) batteries.
batteries can be connected in series?.
as you like up to a few hundred volts or so
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