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October 1961 Electronics World
Table of Contents
Wax nostalgic about and learn from the history of early electronics. See articles
from
Electronics World, published May 1959
- December 1971. All copyrights hereby acknowledged.
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Battery technology experienced a major technology evolution in
the late 1950s similar to the one that took place in the late
1990s. Prior to the 50s, most common portable batteries were
of the carbon-zinc type and were not rechargeable. Nickel cadmium
(NiCad) cells existed, but were not in widespread use largely
because little was known about the chemistry and how it responded
to various charge and discharge cycles. Mercury, NiCad, nickel
metal hydride (NiMH), alkaline-manganese, began gaining popularity
in applications requiring longer battery life and more consistent
discharge characteristics. In the 2000s, lithium polymer (LiPo)
and lithium ion (LiIon) underwent a similar evolution. Still,
all the aforementioned battery types are in use today, so this
article is as relevant now as it was when published in 1961.
New Batteries: Progress or Confusion?
Description, characteristics, and applications of the new
alkaline-manganese and sealed nickel-cadmium types.
By D. B. Cameron
Manager, Sales Engineering, Union Carbide Consumer Products
Co.
Selecting a battery for a radio or instrument is not merely
a dollar-and-cents decision. Proper choice from the many types
now available can have a marked effect on the operation of the
device and on the user's satisfaction and convenience. Every
battery type and electrochemical system offers certain advantages
and limitations. A general understanding of battery characteristics
can eliminate confusion and permit a wise selection.
Fig. 1 - Cut-away illustration of an alkaline-manganese
cell.
Prior to World War II, practically all primary batteries
were the LeClanché or carbon-zinc type. Both flat and
cylindrical cells were available, but choice of a battery for
a particular use presented few problems. Wartime military requirements
stimulated fantastic advances in electronics and created a need
for specialized battery-power sources. Battery research and
development efforts mushroomed. Efficient miniature carbon-zinc
batteries became practical, and new electrochemical systems
were evaluated. The mercury battery system was one result of
this research.
In the years since the war, these efforts have continued.
The mercury battery system and miniature carbon-zinc batteries
were perfected, the transistor was developed, and battery-operated
devices, from toys to radios, gained wide consumer acceptance.
The need for compact, efficient, economical batteries has now
brought two additional electro-chemical systems into use: high-energy
alkaline-manganese batteries and sealed nickel-cadmium rechargeable
batteries.
The owner of a pocket radio powered by penlite cells has
a problem. Shall he use standard flashlight cells, radio-type
carbon-zinc cells, mercury batteries, alkaline-manganese energizers,
or nickel-cadmium batteries? For example, there are eight different
"Eveready" brand penlite cells, each designed for a particular
use. The multiplicity of battery types has caused confusion.
Has there also been progress?
Almost everyone, even a child, recognizes a battery and considers
it a very simple device. Appearances can be deceptive. A battery
is actually a small electrochemical plant. It must do nothing
until power is needed and yet must start operating instantly
when an electrical connection is made. It must operate in any
position and withstand rough handling. A modern battery must
be compact, efficient, foolproof, attractive, and economical;
and it must operate under all orts of adverse conditions. Consider
the characteristics that would be desirable in an ideal battery:
long shelf life, high energy, good light-drain performance,
efficiency on heavy-drain use, reliable intermittent operation,
good continuous service, high amperage, low impedance, high-temperature
stability, low-temperature capabilities, constant voltage, recharge
ability, small size, freedom from leakage, attractive appearance,
and last but not least, it must be inexpensive.
Unfortunately, it is not yet possible to maximize all of
these characteristics in a single battery. In order to supply
each type of user with the. best possible battery for his particular
application, a battery manufacturer must produce a number of
different batteries of the same size and shape, each tailored
to maximize the most essential characteristics for a specific
end use. To obtain the best battery value and satisfaction,
the consumer or the professional who advises and supplies him,
should understand at least the basic characteristics of the
new batteries now available.
Carbon-zinc and mercury batteries have been in use long enough
for most interested technical people to have a general appreciation
of their characteristics. The carbon-zinc system is the workhorse
of the industry. These batteries have the widest availability,
a broad range of desirable characteristics, and the lowest initial
cost. Mercury batteries provide longer life, a more constant
voltage, and lower impedance - but at a higher price. What do
the alkaline-manganese and nickel-cadmium batteries offer?
Alkaline-manganese batteries have a total energy almost equal
to mercury batteries and they are capable of delivering their
rated capacity even on heavy continuous drains where both the
carbon-zinc and mercury systems become inefficient. Furthermore,
this newest electrochemical system provides high amperage, low
impedance, outstanding temperature characteristics, and good
shelf life at a price between carbon-zinc and mercury battery
cost.
Fig. 2 - The type E91 alkaline cell provides
twice the service life obtainable from the standard penlite-type
cell.
The sealed nickel-cadmium system permits a maintenance-free
battery that can be recharged hundreds of times and can be left
discharged without damage. Unfortunately, practical areas of
use are limited by high initial cost and by the fact that energy-per-charge
is often much less than a primary battery can supply.
A discussion of battery performance and applications will
help clarify the relative merits of the alkaline-manganese and
nickel-cadmium battery systems.
Alkaline Primary Batteries
This cell differs from the conventional LeClanché
cell primarily in the highly alkaline electrolyte used. The
cell is a high-rate source of electrical energy. Its outstanding
advantages are derived from the unique assembly of components
and construction methods. See Fig. 1.
Two principal features are a manganese dioxide cathode of
high density in conjunction with a steel can which serves as
a cathode-current collector and a zinc anode of extra high surface
area in contact with the electrolyte. These features, coupled
with the use of a potassium hydroxide electrolyte of high conductivity,
give these cells their very low internal resistance and impedance
and high service capacity.
The cells are hermetically sealed and encased in steel, providing
virtually a leakproof package. Each cell is a nominal 1.5 volts.
The ampere-hour capacity is relatively constant over a range
of current drains and a range of discharge schedules.
The primary advantage of the new system lies in its ability
to work with a high degree of efficiency under continuous or
heavy-duty, high-drain conditions where the standard round cell
is unsatisfactory. Under certain conditions the new alkaline
cells will provide more than ten times the service of standard
round cells. Heavy current drains and continuous or heavy-duty
usage impair the efficiency of the conventional carbon-zinc
cell to the extent that only a small fraction of the built-in
energy may be removed.
On light drains, such as portable radio or instrument use,
alkaline-manganese cells often supply more than twice the service
life (Fig. 2) of carbon-zinc batteries and very nearly equal
mercury battery life. The low impedance of alkaline cells can
improve radio performance by minimizing distortion and their
low temperature characteristics result in good service life
even under outdoor winter conditions.
The good low-temperature performance of alkaline-manganese
batteries completely overcomes the temperature limitation of
mercury batteries and far surpasses standard carbon-zinc cells.
At light to intermediate drains, reasonable service can be obtained
at -40 degrees F and below. This characteristic is particularly
valuable in devices which may be stored or operated outdoors
or in automobiles in winter.
The heavy-drain, high-amperage performance of alkaline-manganese
batteries makes them particularly useful in toys and for photographic
and hobby use. These cells will make practical completely new
types of battery-operated equipment.
The E94 alkaline energizer is a new cell size. The diameter
is the same as a "D" cell but it is only one-half the height.
Two E94 cells will fit in a holder designed for a single "D"
cell. Where it is desirable, and the device will stand the higher
voltage, it is now possible to double the voltage in existing
"D"-cell-powered units. The smaller alkaline cell has a service
capacity equal to a standard "D" cell on heavy continuous drains.
For example, four "1/2 D" cells can be placed in a standard
2-cell flashlight. If the usual PR-2 lamp is replaced by a PR-13
lamp, designed for the higher voltage, the light output will
be doubled. The brilliance will approach that of a 5-cell spotlight.
The E93 "C" size alkaline energizer, like the other alkaline-manganese
cells, on heavy continuous drains will supply up to ten times
the life of a comparable carbon-zinc flashlight cell.
Its first use was in the "Futuramic II" electronic flash
unit manufactured by the Heiland Division of Minneapolis-Honeywell
Regulator Company. The high energy and high amperage of the
alkaline energizers made them ideal for this application.
Electrically powered toys are very hard on batteries because
drains are heavy and the smallest possible cells are usually
used. The majority of toys use "AA" or "C" size cells. The heavy
drain capabilities of alkaline-manganese cells make them ideal
for this use. They not only last several times as long as flashlight
batteries, but they often improve toy performance as well.
When currents of one ampere or more are required for periods
of several hours, larger alkaline-manganese cells must be used.
Both "D" and "G" size cells are available, the latter both as
a unit cell and series-connected to form the 6-volt No. 520
battery. Although the "G" size cell with insulated terminals
("Eveready" No. E97S) is about one-sixth the size and one-quarter
the weight of the No.6 cell used in the hobby field, it gives
over 70 per-cent of the service of the No.6 cell in glo-plug
ignition operation for the engines of model airplanes.
In addition to electronic, toy, hobby, and other heavy-duty
uses, the E95 "D" cell and the 6-volt battery (No. 520) are
particularly adapted for emergency lighting use. Emergency flashlights
or lanterns must be capable of supplying a bright light (high-drain
bulb), they must be capable of continuous operation for the
duration of the emergency (possibly many hours), and they must
operate under adverse temperature conditions. Furthermore, the
batteries must have a good shelf life so they will be capable
of operation when an emergency occurs. These requirements spell
out the important characteristics of alkaline-manganese cells.
The flashlight in an automobile is an emergency light- and in
winter it must be capable of operating when cold!
Battery Economics
The initial cost of alkaline-manganese batteries falls between
that of carbon-zinc and mercury batteries. On all tests they
deliver more service than carbon-zinc batteries and on heavy-drains
or in low-temperature uses, service of alkaline-manganese batteries
will exceed mercury batteries. Unless a flat discharge curve
is essential, the cost-per-hour operation of alkaline-manganese
cells is lower than for mercury batteries, It is also lower
than carbon-zinc batteries in heavy continuous use, but may
be somewhat higher in light intermittent uses. In some cases,
superior electrical device performance, resulting from the better
shelf life and lower impedance of alkaline-manganese batteries,
may offset any increased operating cost.
Rechargeable Batteries
At first glance a rechargeable power source appears to offer
the convenience of primary battery operation without the expense
of replacement batteries. In some circumstances, this could
be true and a rechargeable battery the only economical portable
power source. In other applications a casual appraisal may be
completely misleading. A primary battery may be less expensive
for both the short and long term as well as being more convenient.
Consider the hypothetical case of two men who buy identical
portable radios, operated by four penlite cells. Mr. A is a
machinist working in a noisy shop. He operates his radio ten
hours a day at high volume (45 ma. battery drain) so it can
be heard above the ambient noise. Mr. B uses his radio an hour
a day at low volume (15 ma. battery drain) in a quiet home.
The radios can operate on any of the several types of primary
batteries (assume No. 1015 radio grade carbon-zinc cells @ $1.00
per set of four) or nickel-cadmium cells can be used (No. N46
@ $11.00 per set of four plus approximately $7.00 for a charger).
Mr. A can buy nickel-cadmium cells and a charger, re-charge
them every night and recover his investment (compared to primary
battery operation) in from 2 1/2 to 3 months. A good investment.
On the same basis Mr. B would have to remember to charge his
batteries once a month and would require six years to recover
his investment-and by that time he might well need new nickel-cadmium
batteries because they do not last forever. Obviously a poor
investment. Sealed nickel-cadmium batteries are a fine product
but they should be used only where primary batteries are uneconomical
or impractical.
For use in electronic equipment, any rechargeable battery
should be hermetically sealed so that it is not necessary to
add water and so that gassing on overcharge cannot carry corrosive
vapor into the instrument. Also, the battery should be undamaged
by long periods of storage, charged or discharged, and should
have a low self-discharge rate. Sealed nickel-cadmium batteries
meet these requirements best.
Fig. 3 - Illustration above shows a cut-away
view of a typical sealed nickel-cadmium button cell that is
described in the text.
Sealed Nickel-Cadmium Batteries
The nickel-cadmium battery is a remarkable device and more
than fifty years of successful use have proved this point. Nickel-cadmium
batteries may be recharged many times, have a relatively constant
potential during discharge, and have excellent charge-retention
properties. They will stand more abuse than any other cell,
have good low-temperature performance characteristics, and are
competitive with other systems in terms of cost-per-hour use.
They are true storage batteries using one of the very best electrochemical
systems.
The nickel-cadmium cell has been used in Europe for many
years in its original form as an unsealed cell, for automobile
and truck starting and for fixed installations. Recent technological
advances have made possible the extension of the nickel-cadmium
system to small, hermetically sealed batteries - rechargeable
batteries that are free from the usual routine maintenance,
such as the addition of water. These developments have brought
the economic advantages of re-chargeability to small batteries.
A conventional vented-type nickel-cadmium battery will liberate
oxygen and hydrogen plus entrapped electrolyte (potassium hydroxide)
fumes through a valve. In order to hermetically seal a nickel-cadmium
cell, it is necessary to develop means of using up this gas
inside the cell. This is accomplished as follows:
1. The battery is constructed with excess ampere-hour capacity
in the cadmium electrode.
2. Starting with both electrodes in the fully discharged
state, charging the battery causes the positive (nickel) electrode
to reach full charge first and it starts oxygen generation.
Since the negative (cadmium) electrode has not yet reached full
charge it cannot cause hydrogen to be generated.
3. The cell is designed so that the oxygen formed can reach
the surface of the metallic cadmium electrode where it reacts,
forming electrochemical equivalents of cadmium oxide.
4. Thus, in overcharge, the cadmium electrode is oxidized
at a rate just sufficient to offset input energy, keeping the
cell in equilibrium at full charge.
Fig. 4 - Cut-away view of a cylindrical nickel-cadmium
cell.
This process can continue for long periods. The level of
oxygen pressure thus established in the cell is' determined
by the charge rate used.
Sealed nickel-cadmium cells are available in a variety of
sizes and capacities. See Figs. 3 and 4. These include: button
cells (50-500 ma.-hour capacity), cylindrical cells (450-2000
ma.-hour capacity), and rectangular cells (2-23 ampere-hour
capacity).
The capacity of most nickel-cadmium cells is specified at
the 10-hour rate (current drain required to discharge the cell
in 10 hours). When they are used at higher discharge rates,
the capacity is reduced.
Nickel-cadmium cells have the desirable flat discharge (constant-voltage)
characteristic. As shown in Fig. 5, note that the average voltage
is about 1.2 volts per cell. The initial voltage shown on the
curves is designated as the voltage under load after 10 per-cent
of the ampere-hour capacity has been removed from a fully charged
cell.
Any rechargeable battery will lose charge when stored. Nickel-cadmium
batteries have a lower self-discharge rate than any other present
secondary battery system. More important, the batteries are
not harmed even if not used for long periods of time.
Sealed nickel-cadmium cells experience a relatively small
loss of capacity at operating temperatures, ranging from -20
to +45 degrees C. Within this range, stable discharge voltage
is maintained.
Fig. 5 - Typical discharge voltages at various
drains for sealed nickel-cadmium cells.
With most nickel-cadmium cells, the 10-hour rate should not
be exceeded in constant-current charging. Fourteen hours charging
at this rate will fully charge the cell. Constant-voltage charging,
which is also acceptable, results in a higher initial charging
rate. At the start of charge the current may greatly exceed
the 10-hour rate, but the charging circuit must be designed
so that 10-hour current (or less) flows toward the end of charge.
The battery can be trickle-charged or floated. For maximum
performance in situations of continuous overcharge, with occasional
interruptions, the current should not exceed the 30-hour rate.
These cells will also stand extended overcharge at rates
considerably higher than those recommended for floating. Although
charging at the maximum rate (10 hours) is normally expected
to be completed in 14 hours, cells will not be damaged by occasional
charging at this rate even for several weeks. Continuous overcharging
at higher-than-necessary rates accelerates general degradation
of the cell but complete or sudden destruction will not result
unless the 0-hour rate is exceeded.
A typical, yet simple, charging circuit is shown in Fig.
6. Values of charging current for button and cylindrical cells
range from 5 to 150 ma., depending on cell size, for a 14-hour
charge.
When used in an appropriate application where true advantage
can be taken of their simplicity and rechargeability, sealed
nickel-cadmium batteries can make possible new battery-operated
devices which would otherwise be completely uneconomical.
Fig. 6 - Charging circuit for small sealed
nickel-cadmium batteries.
Conclusion
Is the present multiplicity of batteries worthwhile? Has
there been any real progress? The answer is an unqualified "yes."
New battery systems supplement existing batteries. They improve
the operation of many present devices, make possible new uses,
and offer the consumer new choices so that he can obtain the
best battery buy for his particular device and operating requirements.
Battery and portable-power research and development continue
unabated. Future years will bring still better primary and rechargeable
batteries and probably fuel cells and thermo-electric generators
as well. Thus more new devices will be able to operate electrically
without being tied to a power line.
Posted October 22, 2015
