Breakthrough in Battery Quick Testing
By Isidor Buchmann, President, Cadex Electronics
Inc.
isidor.buchmann@cadex.com
February 2001
When Sanyo, one of the largest battery manufacturers
in the word was asked, “Is it feasible to quick test batteries?”
the engineer replied decisively, “No”. He based his conclusion
on the difficulty of using a universal test method that applies
to all battery applications, — from wireless communications
to mobile computing, and from power tools to forklifts and
electric vehicles.
Several universities, research organizations and private
companies, including Cadex Electronics, are striving
to find a workable solution to battery quick testing. Many
methods have been tried, and most have failed because they
were inaccurate, inconsistent and impractical.
When studying the characteristics relating to battery state-of-health
(SoH) and state-of-charge (SoC), some interesting effects
can be observed. Unfortunately, these properties are cumbersome
and nonlinear, and worst of all, the parameters are unique
for every battery type. This inherent complexity makes it
difficult to create a formula that works for all batteries.
In spite of these seemingly insurmountable odds, battery
quick testing is possible. But the question is, “how accurate
will it be, and how well will it adapt to continuously changing
battery chemistries?” The cost of developing a commercial
quick tester and ease of use are also issues of concern.
The secret of battery quick testing lies, to a large extent,
in understanding how the battery is being loaded. Battery
loads vary from short current bursts for a Global System for
Mobile Communications (GSM) mobile phone, to long and fluctuating
loads on laptops, to intermittent heavy loads for power tools.
The first step in obtaining quick test readings is measuring
the battery’s internal resistance. Resistance measurements
take only a few seconds to complete and provide a reasonably
accurate indication of the battery’s condition, especially
if a reference reading from a good battery is available for
comparison.
Unfortunately, the impedance measurement alone provides only
a rough sketch of the battery’s performance. Various battery
conditions affect the readings. For example, a fully charged
battery that has just been removed from the charger shows
a higher impedance reading than one that has rested for a
few hours after charge. The elevated impedance is due to increased
interfacial resistance present after charging. Allowing the
battery to rest for an hour or two will normalize the battery.
Temperature also affects the readings. In addition, the chemistry,
the number of cells connected in series and the rating of
a battery influence the results. Many batteries also contain
a protection circuit that further distorts the readings.
The
evolving lithium ion battery
The Li-ion battery has not yet matured. According to Moli
Energy, a large manufacturer of Li-ion batteries, the
chemical composition of Li-based batteries changes every six
months. New chemicals are discovered that provide better load
characteristics, higher capacities and longer storage life.
Although beneficial to users, these improvements wreak havoc
with battery testing equipment that base their quick test
algorithms on fixed parameters. The following paragraphs explain
why these changes in battery composition affect the results
of a quick tester.
The early Li-ion batteries, notably the coke-based variety,
exhibited a gradual drop of voltage during discharge. With
newer graphite-based lithium-ion batteries, flatter voltage
signature is achieved. Such batteries provide a more stable
voltage during most of the discharge cycle. The rapid voltage
drop only occurs towards the end of discharge.
A ‘hardwired’ tester looks for an anticipated voltage drop
and estimates the SoH according to fixed knowledge that is
available as a reference. If the voltage-drop changes due
to improved battery technology, erroneous readings will result.
Different metals for the positive electrode alter the open
terminal voltage. Manganese, also referred to as spinel, has
a slightly higher terminal voltage compared to the more traditional
cobalt. In addition, spinel ages differently from cobalt.
Although the cobalt and spinel systems belong to the Li-ion
family and its identity is unknown to the user, differences
in readings are likely when the batteries are quick tested
side-by-side.
The Li-ion Polymer has a dissimilar composition to the Li-ion
and responds differently when tested. Instruments capable
of checking Li-ion batteries may not provide reliable readings
when quick testing Li-ion Polymer batteries.
Commercial
quick test platforms
A battery quick test must be capable of adapting to new chemical
combinations as introduced from time to time. Cadex solves
this problem by using a self-learning fuzzy logic algorithm.
Used for various other applications to measure analog variances,
fuzzy logic is known to the industry as a universal approximator.
In conjunction with a unique learning algorithm, this system
is capable of adapting to new trends. Similar to a student
adapting to the complexity of a curriculum, the system learns
with each battery tested. In fact, the more batteries that
are serviced, the higher the accuracy becomes.
The Cadex QuickTest is built on the new C7000 Series
battery analyzer platform. This system features interchangeable
battery adapters that contain the battery configuration codes,
also known as C-codes. The C-code is unique for each battery
type. When installed, the adapter sets the analyzer to the
correct battery parameters (chemistry, voltage rating, etc.).
Figure 1 illustrates the two-station Cadex C7200
battery analyzer equipped with the QuickTest™ feature.
Figure 1:
Cadex C7200 battery analyzer with QuickTest function.
To enable quick testing, the battery adapters must also contain
the matrix settings for the battery serviced. While most common
battery adapters will include the matrices at time of purchase,
the user is asked to enter the information on adapters that
have not yet been prepared for quick testing. This can be
done in the field by ‘scanning’ the working battery. The Learn
program of the C7200 performs this task by applying charge-discharge-charge
activities on the test battery. Similar to downloading a program
into the PC, the information derived from the battery sets
the matrices and initiates the QuickTest function. The Learn
programs last about five hours and needs to be done only once
per battery.
With only one battery scanned, the confidence level will
be ‘marginal’ because only one learning cycle is available.
Running additional batteries on the lean program fills
the ‘capacity registers’ and the confidence level increases.
Like a bridge that needs several pillars for proper support,
the most accurate quick test results are achieved by scanning
individual batteries with state-of-health readings of around
100%, 80% and 60%.
Early lab tests have revealed amazingly accurate SoH test
results using this method. More tests will be needed to evaluate
the consistency and repeatability on a broad spectrum of batteries
that are in common use. This includes Lithium Ion, Nickel
Metal Hydride, Nickel Cadmium, and Lead Acid chemistries.
Can
the system learn incorrectly?
Once the learning cycles of a given battery type have been
completed, the matrix settings are firm and resilient to testing
any battery. Spoilage is only possible if a number of bad
batteries are put on the learn program. Such would be the
case when ‘scanning’ a batch of batteries that have not been
properly formatted or have been in prolonged storage. Before
a new vector reading is stored as a learned reference, its
integrity is checked. Readings from defective batteries are
rejected.
If a battery adapter has lost its integrity as part of “bad
learning,” the matrix setting can be erased and re-taught.
Once a good set of matrices are on hand, users may want to
exchange this information with each other. Copying battery
adapters by inserting the learned adapter into the analyzer
will achieve this. Another method will be ‘Webcasting’ the
matrices over the Internet.
The QuickTest can be performed with charge levels
between 20 and 90 percent. Within this range, different charge
levels do not affect the readings. If the battery is insufficiently
charged, or has too high a charge, a message appears and the
analyzer automatically applies the appropriate charge or discharge
to bring the battery within testing range. The test lasts
about three minutes per battery. Each station of the C7200
battery analyzer can test batteries independently.
Artificial intelligence, the heart of the Cadex QuickTest
The Cadex QuickTest works on a neuro-logic network
based on fuzzy logic and resembles the thinking process of
the human brain. First, multiple vector settings are fed to
the micro controller and fuzzified. The data is then processed
through parallel logic. The information is averaged and weighted
according to the battery application. Figure 2 illustrates
the general structure of such a network:
Figure 2:
Flowchart of the neuro-network based on fuzzy logic
The raw data consisting of three or more items flows through
the input layer. Vectors leading from the input layer are
weighted and the derived values are passed through a function
in the hidden layer. The information then proceeds towards
the output by using another vector set.
The weights are highly significant and function as the learning
facility of the network. For example, a run would proceed
with a certain set of weights. If the result is off by a certain
range, the weights are changed and the process is re-run.
This process repeats itself until either a certain number
of iterations have passed or the algorithm produces the correct
output.
Of course, artificial intelligence is a complicated subject,
and greater details are beyond the scope of this article.
In respect to complexity, Dr. Lotfi A. Zadeh, Professor
of the University of California and developer of the fuzzy
logic, spoke these famous words, “As complexity rises,
precise statements lose meaning and meaningful statements
lose precision.”
Battery
testing and the Internet
Increasingly, the Internet plays a pivotal role in assisting
battery testing. One application is to send all battery test
results to a central database. With this information on hand,
the battery manufacturer can perform extensive battery analysis
based on battery type, geographic area and user pattern. Field
failures can be detected quickly and the appropriate corrections
applied.
Another application of the Internet is establishing a global
database for all major battery types, complete with vector
settings. With compatible systems, the user would be able
to select and download battery information from a central
database. Batteryshop™, a software product offered
by Cadex provides such a service. Batteryshop’s database lists
all major commercial batteries in circulation, complete with
battery specifications and matrix information. Clicking the
mouse on the desired battery programs the analyzer to the
correct parameters. The user only needs to slide the battery
into the configured adapter and the system takes care of the
rest.
Collaborating with battery manufactures will enable Cadex
to create the most accurate matrix settings. Manufacturers
welcome such a system because it shortens the development
cycle of new battery types, reduces beta testing and puts
the manufacturer in closer contact with the battery user.
Another powerful feature of the Internet is downloading new
software for hardware upgrades. Since battery quick testing
is still in its infancy, improved software will be available
that can upgrade existing equipment to the latest technological
findings.
Summary
When studying the history of time, one can observe periods
when the world focused on certain technologies. Much effort
was place on the clock in the 1700s, steel construction and
railways during the 1800s, the atomic bomb in the World War
II, and the Internet during the last two decades. Technology
comes, perfects itself, and then proceeds at a more controlled
pace. It leaves behind a legacy, a stepping-stone, which our
forefathers embraced to advance to where we are today.
Much activity is visible in battery quick testing today.
There is a race towards commercializing a product that is
accurate, easy to use and cost effective. With modern microelectronics,
such a task is more feasible today than ever. The true winner
of the battery quick test challenge may not be an individual
or organization that amasses the largest number of patents,
but a company that can truly offer a product that works.
This article contains excerpts from the second edition book
entitled Batteries in a Portable World — A Handbook
on Rechargeable Batteries for Non-Engineers. In the book,
Mr. Buchmann evaluates the battery in everyday use and explains
their strength and weaknesses in laymen’s terms. The 300-page
book is available from Cadex Electronics Inc. through book@cadex.com, tel. 604-231-7777 or most bookstores.
About the Author
Isidor Buchmann is the founder and CEO of Cadex Electronics
Inc.in Vancouver, British Columbia, Canada. Mr. Buchmann has
a background in radio communications and has studied the behavior
of rechargeable batteries in practical, every day applications
for two decades. The author of many articles and books on
battery maintenance technology, Mr. Buchmann is a well-known
speaker who has delivered technical papers and presentations
at seminars and conferences around the world. He can be reached
at Tel: 604-231-7777; Fax: 604-2317755; E-mail: Isidor.Buchmann@cadex.com.
About the Company
Cadex Electronics Inc.
is a world leader in the design and manufacture of advanced
battery analyzers and chargers. Their award-winning products
are used to prolong battery life in wireless communications,
emergency services, mobile computing, avionics, biomedical,
broadcasting and defense. Cadex products are sold in over
100 countries.
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