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Editorial.
Welcome
to issue 17 and a big thank you for continuing to subscribe to
our
publication, we appreciate your
support.
First
off all, we would like to appologise for the length of time between
this and
the
previous issue of our publication. We have been working on a number
of new
projects
and simply didn't have enough time to complete this ezine until
now.
As I
have mentioned in previous issues, it is becoming increasingly
difficult to
create
articles that avoid covering old ground. As a result, we have
decided to
reduce
the number of articles from 2 to 1. We continue to post each issue
to
our web
site and the information available is now considerable. Please feel
free
to copy
or print as many articles as you like.
Please
note that we will not accept submissions from free email addreses.
We
were
inundated with failed delivery messages when sending out our
previous
issue
and spent some hours trying to re-send the publication. Private
email
adress
subscription only from now on please.
Enjoy the content and hope you
will continue to subscribe to our
publication.
Happy
Reading!
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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 Eighteen years and
has designed
charging equipment and battery monitors for some of the world
largest companies.
_____________________________________________________________________
_____________________________________________________________________
ARTICLE: Fault Finding. Author: Alan
Fidler.
One of
the most difficult aspects of battery and charger maintenance is
actually
diagnosing what has happened when something
eventually goes wrong. With enough
experience, it is relatively simple but
even I find it tricky in some circumstances.
The best
way to start, it to examine the complete installation, stage by
stage, keeping
notes on
what is found and where. This is the best way to ensure that there
are enough
clues
upon which to piece together a failure sequence. In this respect,
the job of fault
finding
is rather like a criminal investigation.
The
first thing to check is fuses. Are they intact or have they
ruptured?
Use a
digital continuity meter set to ohms to confirm the status of
each link. A healthy
fuse
will show zero ohms, a failed fuse will show open circuit. Remember
to write down
the
status of each fuse link on paper.
Next,
examine the batteries. Measure the voltage across each battery and
make sure
they are
within a voltage band of 1.5 to 2.2 volts per cell for lead acid and
0.7-1.41 volts
per cell
for nicad cells. Many industrial chargers incorporate short circuit
protection
and will
not deliver charging current into batteries which fall outside the
above limits.
Check
the battery casing for signs of heat where they show an abnormal
result in the
above
tests. A deeply discharged battery may show a reverse voltage and
this will
certainly mean replacing it before
proceeding.
Having
confirmed that the batteries are OK or following replacement, the
next stage
involves
the charger components themselves. Most transformer based
systems
incorporate full wave bridge rectifier or
half control diode/thyristor blocks. In either
case,
the diodes should exhibit a volts drop of between 0.55 and 0.8 volts
DC using
a diode
tester. The positive probe is connected to the anode side of the
diode which
would be
rectifier negative in either configuration or either AC terminal in
full wave
bridge
rectifiers to test the forward diodes. Connect the negative probe to
each AC
termination in both configurations or
rectifier positive to test the forward diodes in
full
wave bridge rectifiers.
Look at
the transformer now by examining the windings where they are visible
for
obvious
signs of heat. A burnt out transformer will have black, heat
damaged
insulation and fused windings. If in doubt,
take the transformer to a local motor
rewind
specialist and ask them to check it for you. Burnt out
transformers
are
usually the result of over rated fuses or a total absence of one in
the mains
supply.
Rarely do industrial grade transformers suffer this kind of damage
when
properly
fused.
Lastly,
check any large capacitors fitted to the system for obvious signs
of
heat
damage. A capacitor can be checked by taking it out of circuit and
testing
it with
a digital meter set to ohms. A healthy electrolytic capacitor will
charge
up via
the test probes and the ohms reading will steadily increase as it
does so.
Any
capacitors which show zero ohms should be regarded as suspicious
and
will
need to be tested using a current limited bench type power
supply.
General
heat damage on cables and crimps needs to be examined closely.
A
loose
connections can result in localised arcing and therefore heat which
cracks
crimp
insulation and damages cable insulation. Heat damage which is
evenly
distributed across the whole length of a
cable indicates excessive current flow.
This may
have been caused by a short circuit condition or uncontrolled
current
flow,
normally the result of a short circuit diode or thyristor or
reversed battery
connections or battery polarity through
deep discharge.
Use all
of the notes you have kept to try and ascertain the failure
sequence. We
know
that fuses fail because of excessive current. If we can determine
why the
excessive current flowed in the first
place, we will know what failed first and how
the
installation was compromised.
Damaged
mains fuses may be the result of a switch-on surge, excessive
charging
current
caused by a failed component or transformer primary failure.
Check the
components first then examine the
transformer. If all is ok, replace fuse with
type "T"
Anti-surge type and test the charger.
Buckled
batteries are the result of excessive heat. If the charger is
functioning
normally
upon replacement of the cells, it is likely that the original
batteries were
exposed
to a large discharge, perhaps as the result of a short circuit or
load
failure.
Consider fitting a fuse in series with the charger supply to the
batteries
where
component failure has resulted in excessive charging current
and
consequential heat damage to the
cells.
Remember: Look after your batteries and
your batteries will look after you!
______________________________________________________________________
______________________________________________________________________
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______________________________________________________________________
______________________________________________________________________
CLASSIFIED
ADS:
12 & 24V DC
DIMMER SWITCHES
*Adjust 12 or 24V lamps from a dim
glow to bright light with a CBC Dimmer
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*Extends bulb life and reduces battery
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*Easy to install with integral
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*20 year industrial design
life*
________________________________________________________________________
________________________________________________________________________
READERS QUESTIONS.
Questions from in-house
1.
What causes batteries to buckle?
This is usually the result of heat causes by
over charging or over discharging the cells.
2. What is the maximum charging rate for
sealed lead acid batteries?
Normally 1/20th of the battery capacity.
Check the manufacturers data sheets
for
confirmation.
_________________________________________________________________________
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