Conductance testing has recently been added to the IEEE draft standard
for testing sealed valve regulated lead acid batteries. Extensive field test results were presented
to Bellcore's T1Y1 Group, a Bellcore symposium on passive battery monitoring
and testing, the International Lead Zinc Research Organization and the Battery
Council International conferences in May of 1992, and the International
Telecommunications Energy Conference in October of 1992. Many battery manufacturers are using
Midtronics Conductance Testers, as well as every Regional Bell Operating
Company, global telecommunications providers and manufacturers and users of
Uninterruptible Power Supply (UPS) systems.
This acceptance of conductance methodology has resulted in a series of
questions about conductance testing.
The following are answers to some
of the most frequently asked questions:
A. Conductance
describes the ability of a battery to conduct current. It is the real part of the complex
admittance. Various test data have
shown that at low frequencies, the conductance of a battery is an indicator of
battery state-of-health showing a linear correlation to a battery's
timed-discharge capacity test result. This can be used as a reliable predictor
of battery end-of-life.
A. In
simplest technical terms, Ohmic technology is based on Ohm's law, which
expresses the relationship between volts, amperes and ohms in an electrical
circuit. Ohm's law can be expressed as
follows: Volts (E) = Amperes (I) x Ohms (R).
If any two of the three values of voltage (volts), current (amperes) or
Resistance (Ohms) are known, the third value can be calculated using the above
expression of the law.
Thus,
Ohmic technology attempts to use voltage and current to determine the resistive
characteristic of a battery. Higher
resistance equates to a reduced ability to produce current. This characteristic is translated into a
measurement of resistance or impedance (Ohms) in some Ohmic technologies; more
recent technology uses a converse measurement, called conductance.
A. Through
years of laboratory and field-based research, conductance has been found to
correlate directly with battery capacity as measured in a timed discharge
test. This correlation is nearly
linear, meaning that if conductance can be measured, timed-discharge capacity
can be predicted. Since voltage and
specific gravity testing are not predictive, timed discharge testing is very
time-consuming and expensive, and impedance testing does not correlate directly
and linearly with timed discharge capacity, conductance testing is a very
effective and economical alternative.
A. Simply
by connecting the two test set leads to the positive and negative posts of the
cell or battery under test, a measurement is taken in a matter of seconds. There is no need for additional leads to be
connected to the ends of the string, or for clamp-on current measurements. A conductance measurement is displayed in
Mhos or Siemens, sometimes abbreviated with a "G".
A. A
significant number of tests on a variety of valve regulated lead acid (VRLA)
batteries demonstrate that conductance is predictive of battery
state-of-health. Since conductance is
directly related, and very nearly linear with timed-discharge capacity, a
reading of the percentage of a known conductance reference value is a reliable
predictor of a capacity test result.
The conductance tester gives a quantitative measurement in Mhos (or
Siemens), as well as a qualitative indication (percent of reference) of a
battery as related to a standard.
A. Unlike
other testing techniques that require interpretation and mathematical
calculation, conductance readings can be read instantly and can be related
directly to the condition of the battery being tested.
Q. Since
the qualitative conductance test requires a standard, how can that standard be
established?
A. The
most effective method for the establishment of a standard requires the
performance of a timed discharge test to locate a cell or battery that performs
to 100% of the rated discharge capacity.
A conductance test can then be performed and a reference
established. A sample of 30 or more new
batteries can also be used to establish a standard. Without a set reference value, conductance testing can still be
utilized to trend state of health, as batteries can be monitored through
periodic conductance readings and the observation of deterioration over time.
Q. Can
conductance testing be used to evaluate the quality of inter-cell connections?
A Yes.
Since a conductance reading of a cell plus an inter-cell connection can easily
be related to the conductance of the cell alone, conductance provides a very
simple and reliable indication of the system's inter-cell connection quality.
Q. Can
Midtronics conductance testers measure the condition of sealed valve-regulated
batteries as well as flooded cells?
A. Yes.
Correlation studies have been performed on a significant number of valve
regulated cells. These studies have
shown that conductance test results are very predictive of battery timed
discharge capacity, while voltage measurements are shown to be of little
value. This data has been presented to
a number of international organizations. Additionally, recent data includes
gelled batteries, and Midtronics' testing will soon include NiCad batteries.
Q. What
kinds of batteries and cells can be tested utilizing conductance?
A. Typically
any 2 Volt to 12 Volt, lead-acid, 5 to 2000 ampere-hour cells can be tested.
Q. Can
Nickel Cadmium (NiCad) batteries and cells be tested utilizing conductance?
A. The
Micro Celltron (CTM) from Midtronics will accurately measure the voltage and
conductance of Nickel Cadmium batteries.
Conductance will measure and identify gross failures of NiCad batteries. The Celltron will report hard shorts
identified through low-voltage, and is a useful tool in testing the application
of NiCad battery systems.
The
feature of identifying the decline and forecasting the failure of battery
cells, a superior feature of the Micro Celltron, is not as applicable when
testing NiCads. Based upon their
construction and chemistry, all NiCads will measure consistently (good) until
there is a gross failure indicating the end of life. The Celltron will indicate this gross failure after the fact, a
limitation that is true of all Ohmic measuring devices, including all existing
impedance and resistance testers on the market.
As
mentioned above, the Celltron contains a low voltage alarm, settable by the
user to a minimum of 1.50 volts DC cell.
The Celltron will report an audible alarm when testing single cell
NiCads falling below the voltage benchmark.
Additionally, the Micro Celltron will not test any battery or cell where
the measured voltage is below 1.0 Volts DC, which would include any badly
discharged or shorted NiCad cells.
For
more information on the testing, trending and analysis of NiCad batteries,
please contact Midtronics.
Q. Can
a Midtronics conductance test be made while the battery is on float?
A. Yes.
The current test technology enables successful testing of batteries while on
float charge. In certain cases an
excessive amount of electrical noise current can interfere with any test
method.
Q. Does
the Midtronics conductance tester need to be plugged in to AC power?
A. No. Midtronics Conductance testers require no
external AC power. Midtronics testers
derive test power by removing a small (less than 1 AH) load from the battery
under test. Additionally, the testers
are powered by an on-board 9-volt alkaline battery for the test data review,
test configuration, portable printing and transfer to PC.
Q. Can
the signal from the Midtronics conductance tester interfere with or damage
electronic equipment or cause danger to a defective cell?
A. No.
Midtronics conductance testers do not apply a large current to the battery
under test, as does other test equipment.
Midtronics testers apply a signal frequency less than one Amp;
therefore, it is highly unlikely that over-current damage to sensitive
electronic equipment could result in the event of a defective cell. Testing on communication systems shows that
conductance testing does not interfere with telephone signals. Users should be
aware that other types of battery test equipment (non-conductance methods) do
use AC power to send a large current though the battery, which may affect
sensitive electronic devices.
A. All
Midtronics conductance testers are hand-held portable instruments. They are built to very rugged standards, yet
weigh less than 2 pounds (1 kilogram) each.
The testers are easily transportable and each includes some form of
protective carrying case.
Q. How
long has the Midtronics conductance test method been used for testing
batteries?
A. The original technology was developed by
Motorola in the 1970s for testing automotive batteries. Today's products are manufactured under
license from Motorola, and include many new patents in North America, Europe and
Japan. Midtronics has been developing
and manufacturing conductance testers for more than ten years, and customers
include the world's major battery manufacturers, major automotive
manufacturers, telecommunications providers, electric power utilities, UPS
manufacturers, and organizations in a variety of other industries. Midtronics has manufactured tens of
thousands of battery conductance testers under the PowerSensor™, Midtron®, and
Celltron® brands, as well as various private labels. Our products are manufactured and used extensively throughout the
globe, making Midtronics the world leader in battery management technology.
Q. Has
conductance testing been proven and accepted by the international community?
A. Yes.
Extensive data has been gathered by the global telecommunications industry,
battery manufacturers worldwide, international rail and transportation
providers, and the electric power industry.
This data has been presented to the IEEE Standards Committee, which now
includes conductance testing in its draft standard for testing sealed
valve-regulated batteries.
Additionally, The data has also been presented to the International Lead
Zinc Research Organization, the Battery Council International, and the
International Telecommunications Energy Conference.
A. Yes,
many papers have been presented which include correlation data. Midtronics will provide correlation data and
customer references upon request. Many
technical papers are currently posted on our website at www.midtronics.com.
Q. What
is the optimal point of contact when making a conductance test?
A. Making
direct contact with the lead post area is ideal for an accurate test
result. In order to facilitate this
contact (which can be difficult depending on the battery post design),
Midtronics offers a variety of battery test interfaces, including clamps and
contact probes of differing sizes.
Contact with stainless steel post hardware will skew test results.
Q. What if I cannot test my batteries directly
at the post because of physical constraints?
A. If
battery and cabinet construction makes testing at the post or lead strap
impossible, BE CONSISTENT with every test.
If you must test on the hardware, test in the same spot for every cell,
every time. If you are inconsistent with
your probe or clamp placement, your reading will be inconsistent as well.
Q. What
is a Kelvin Connection and why is it needed for accurate conductance
measurement?
A. The
Kelvin Connection is a four-point connection that is used in order to eliminate
the resistance of the test interface material.
It is necessary to ensure an accurate conductance measurement that is
not affected by test interface resistance.
All Midtronics testers and monitors utilize a Kelvin connection.
A. Yes. The actual temperature of the battery must
be considered when making a conductance test.
Battery conductance reference values (or baselines) assume the optimal
battery operating temperature of 77° Fahrenheit (25 ° Celsius). A calculation can be made to compensate for
temperature variation. The Micro
Celltron can automatically calculate the change in percent of reference, or a
chart detailing this calculation is available from Midtronics for other testers
and monitors.
Additionally,
an Infrared Temperature Sensor is available from Midtronics to accurately
determine battery temperature.
A. Yes. The new Celltron inFORM software and data logger
from Midtronics facilitates the downloading and manipulation of data collected
with the Micro Celltron. Data is
presented in a graphical format and can be utilized for trend analysis as well
as historical archiving. An infrared
strip printer is also available for on-site printing and record keeping. inFORM can be downloaded over the Internet
FOR FREE at www.midtronics.com.
Product Information Questions:
A. The
Micro Celltron cables are fixed at the current length to ensure that the cable
wiring does not skew the electronic measurements. The DB9 connector contains a calibration shunt that
"zeroes" out any interference in the conductance measurements. Any change or alteration to the cable
assembly or length would interfere with the accuracy of the measurement.
Q. How
can I test large amp batteries or batteries above 10,000 Siemens with the Micro
Celltron?
A. For
2V, 4V or 6V batteries, there is a method to "trick" the Micro
Celltron to test batteries with Siemens values above 10,000 and obtain an
estimate of the conductance value of the cell.
The procedure is not exact, and thus should not be used as a reference
or absolute value. It simply represents
a method for a customer who has a large battery to obtain a conductance value
using the Micro Celltron:
1.
Upon testing cells that reach the threshold of the CTM (over 9999 G),
simply connect the tester across 2 consecutive cells in the string, as if they
were one individual cell. Do NOT
attempt this on 8V, 10V or 12V batteries as the 16V fuse will likely be blown!
2.
The voltage of the test will be 2X the individual cell, and the
conductance will be approximately 50%.
Multiply the conductance by two to get the estimated conductance of the
individual cell. Note that the voltage
alarm will sound on the Micro Celltron during the test.
3.
Continue through the string testing cells 1&2, 2&3, and so
on. Note that you will not be able to
tell a bad cell directly, but can interpret one from the string results. For instance:
Cell
test 1&2 = 5500 Siemens
Cell
test 2&3 = 3200 Siemens
Cell
test 3&4 = 3700 Siemens
Cell
test 4&5 = 5650 Siemens
Cell
#3 is probably an issue!
Contact:
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Banchory
Aberdeenshire
AB31 5WS
Phone: +44
(0) 1330 823950
Fax: +44
(0) 1330 823966
Email: info@skylark.co.uk