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Battery Analyzers for Maintenance-Free Batteries
In the past, the purpose of battery analyzers
was to restore NiCd batteries affected by ‘memory’. With today’s
nickel-free batteries, memory is no longer a problem and the
modern battery analyzer assumes duties other than conditioning
weak batteries. In an environment with nickel-free batteries,
the purpose of an analyzer is shifting to performance verification,
quality control, quick testing and quick priming.
 Common
sense suggests that a new battery should always perform flawlessly.
Yet even brand new batteries do not always meet manufacturer's
specifications. With a battery analyzer, all incoming batteries
can be checked as part of a quality control procedure and
a warranty claim can be made if the capacity drops below the
specified level toward the end of the warranty period.
The typical life of a Li-ion battery is
300 to 500 discharge/charge cycles or two to three
years from the time of manufacturing. The loss of battery
capacity occurs gradually and often without the knowledge
of the user. The function of the battery analyzer is to identify
weak batteries and “weed’ them out before they become a problem.
A battery analyzer can also trouble-shoot the
cause of short runtimes. There are several reasons for this
common deficiency. In some cases, the battery may not be properly
formatted when first put in service; or the original charger
does not provide a full charge. In other cases, the portable
device draws more current than specified. Many of today’s
battery analyzers can simulate the load signature of a digital
device and verify the runtime according to the load requirements.
Lithium-based batteries are sensitive to aging.
If stored fully charged and at elevated temperatures, this
battery chemistry deteriorates to a 50 percent performance
level in about one year. Similar performance degradation can
be seen on NiMH batteries when used under these conditions.
Although still considered new, the user will likely blame
the equipment rather than the battery for its poor performance.
The analyzer can isolate this problem.
Before adding new batteries to the battery fleet,
a battery analyzer can be used to perform a spot check to
ensure proper operation. If a battery shows low performance
due to aging, the inventory practices may be changed to the
‘just in time’ method. Storage facilities with improved temperature
control may also be sought.
An important new function of a battery analyzer
is the ability to quick test batteries. No longer is it necessary
to guess a battery’s condition by reading the terminal voltage,
measuring the internal resistance or in enrolling lengthy
charge and discharge cycles to determine its performance.
Modern quick test programs using artificial intelligence are
amazingly accurate and work independently of SoC.
Battery quick testing is finding a ready market
niche with mobile phone dealers. This feature saves money
because batteries returned under warranty can be tested. Replacements
are only issued if a genuine problem is found. Once battery
quick testing has been further refined, this technology will
also find applications in the fields of biomedical, broadcast,
aviation and defense.
Battery Throughput
The quantity of batteries which an analyzer is
capable of servicing depends on the number of battery bays
available. The type of service programs and the conditions
of the batteries serviced also play a role. Li-ion and
lead acid batteries take longer to charge than nickel-based
packs. Analyzers with fixed charge and discharge currents
require added time, especially for larger batteries.
 The four-station Cadex 7400 battery analyzer is
capable of processing four nickel-based batteries every 4
to 8 hours on a full-service program. Based on two batches
per day (morning and evening attendance) and 20 working
days per month, one such analyzer can service 160 batteries
every month. The throughput of batteries with ratings higher
than 2000mA or those that need to be charged and discharged
at lower C-rates will take longer. To allow extra analyzer
capacity, including reconditioning of old batteries, one four-station
analyzer is recommended for a fleet of 100 batteries.
When first servicing a fleet of batteries with
a battery analyzer, extra runtime will be required, especially
if a large number of batteries need to be restored with the
recondition cycle. Once the user-defined target capacity has
been reached, maintaining that level from then on will be
easier and take less time. When first installing a battery
maintenance program, some older packs will likely need replacing
because not all batteries recover with exercise and recondition
programs.
Quick test methods require the least amount of
time. The Cadex Quicktest™ available on the Cadex
7000 Series takes three minutes per battery. The time
is prolonged if a brief charge or discharge is needed prior
to testing. A charge or discharge is applied automatically
if the battery resides outside the SoC requirements of 20
to 90 percent. Unlike the maintenance program, the Cadex
Quicktest™ does not improve the battery’s performance;
it simply measures its SoH.
The Ohmtest™measurement of the Cadex
7000 Series analyzer takes ten seconds to complete.
Large numbers of batteries can be examined if the packs are
charged prior to the test. Measuring the internal battery
resistance works reasonably well if reference readings are
on hand. However, there are batteries that measure good internal
resistance but do not perform well. This is especially common
with nickel-based chemistries.
There are a number of factors which affect the
accuracy of the internal resistance readings, one of which
is SoC and the settling time allowed immediately after a recharge.
A newly charged battery exhibits higher resistance readings
compared to one that has rested for a while. The increased
interfacial resistance present after charging causes this.
Allow the battery to rest for one hour or more before measurement.
Temperature and the number of cells connected in series also
affects the readings. Many batteries contain a protection
circuit that distorts the readings further.
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