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LW1DSE > TECH 31.08.08 18:04l 266 Lines 13820 Bytes #999 (0) @ WW
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The nickel-cadmium battery (commonly abbreviated NiCd and pronounced
"nye-cad" is a type of rechargeable battery using nickel oxide hydroxide and
metallic cadmium as electrodes.
The abbreviation NiCad is a registered trademark of SAFT Corporation
and should not be used to refer generically to nickel-cadmium batteries,
although this brand-name is commonly used to describe all nickel-cadmium
batteries. On the other hand, the abbreviation NiCd is derived from the
chemical symbols of nickel (Ni) and cadmium (Cd), though it isn't to be
confused with a chemical formula.
There are two types of NiCd batteries: sealed and vented. This
article mainly deals with sealed cells.
Contents:
1 Advantages
2 Applications
3 Voltage
4 History
4.1 Production in the United States
4.2 Recent developments
4.3 Popularity
5 Nickel-Metal Hydride
6 Battery Characteristics
6.1 Comparison to Other Batteries
6.1.1 Advantages
6.1.2 Disadvantages
6.2 Availability
7 Characteristics
7.1 Charging
7.2 Inspecting
7.3 Charge condition
7.4 Charging method
8 Electrochemistry
9 Problems with NiCd
9.1 Overcharging
9.2 Cell reversal
9.3 Memory and lazy battery effects
9.4 Dendritic shorting
9.5 Environmental consequences of Cadmium
1) Advantages:
The principal advantages of NiCd over other rechargeable types is
lower weight for a given quantity of stored energy, good charging efficiency,
small variation in terminal voltage during discharge, low internal resistance,
and non-critical charging conditions. They can be used in place of regular
batteries in most applications.
2)Applications:
Sealed NiCd cells may be used individually, or assembled into battery
packs containing two or more cells. Small NiCd dry cells are used for portable
electronics and toys, often using cells manufactured in the same sizes as
primary cells. When NiCds are substituted for primary cells, the lower
terminal voltage and smaller amperehour capacity may reduce performance as
compared to primary cells.
Specialty NiCd batteries have a niche market in the area of cordless
and wireless telephones, emergency lighting, model airplanes, as well as power
tools.
With a relatively low internal resistance, a NiCd battery can supply
high surge currents. This makes them a favourable choice for remote controlled
electric model aeroplanes, boats, and cars, as well as cordless power tools
and camera flash units. Larger flooded cells are used for aircraft starting
batteries, electric vehicles, and standby power.
3) Voltage:
Nickel-cadmium cells have a nominal cell potential of 1.2V. This is
lower than the 1.5 V of many popular primary cells, and consequently they are
not appropriate as a replacement in all applications. Unlike common primary
cells, a NiCd cell's terminal voltage only changes a little as it discharges.
Because many electronic devices are designed to work with primary cells that
may discharge to as low as 0.90 to 1.0 V per cell, the relatively steady 1.2V
of a NiCd is enough to allow operation. Some would consider the near constant
voltage a drawback as it makes it difficult to detect when the battery charge
is low.
NiCd batteries used to replace nominally 9-V "transistor radio"
batteries usually only have six cells, for a terminal voltage of 7.2 volts.
While most pocket radios will operate satisfactorily at this voltage, some
manufacturers such as Varta made 8.4 volt batteries with seven cells, for more
critical applications.
12 V NiCd batteries are made up of 10 cells connected in series.
4) History:
Waldemar Jungner of Sweden created the first nickel-cadmium battery
in 1899 which was based on Thomas Edison's first alkaline battery, with the
difference that Cadmium (Cd) instead of Iron (Fe) was used as the cathode. At
that time the only direct competitor was the lead-acid battery which was less
physically and chemically robust. With minor improvements to the first
prototypes, energy density rapidly increased to about half of that of primary
batteries, and significantly greater than lead-acid batteries. In 1906,
Jungner established a factory in Sweden to initially produce industrial nickel
-iron and later nickel-cadmium batteries.
4.1) Production in the United States
The first production in the United States began in 1946. Up to this
point, the batteries were "pocket type," constructed of nickel-plated steel
pockets containing nickel and cadmium active materials. Around the middle of
the twentieth century, sintered plate nickel-cadmium batteries became
increasingly popular. Fusing nickel powder at a temperature well below its
melting point, using high pressures creates sintered plates. The plates thus
formed are highly porous, about 80 percent by volume. Positive and negative
plates are produced by soaking the nickel plates in nickel and cadmium active
materials, respectively. Sintered plates are usually much thinner than the
pocket type, resulting in greater surface area per volume, and higher
currents.
In general, the more surface area of reactive materials in a battery,
the lower its internal resistance.
4.2) Recent developments:
In the past few decades, this has resulted in nickel-cadmium batteries
with internal resistance as low as alkaline batteries. Today, all consumer
nickel-cadmium batteries use the "jelly-roll" design. This design incorporates
several layers of anode and cathode material rolled into a cylindrical shape.
4.3) Popularity:
Advances in battery manufacturing technologies throughout the second
half of the twentieth century have made batteries increasingly cheaper to
produce. Battery-powered devices in general have increased in popularity. As
of 2000, about 1.5 billion nickel-cadmium batteries were produced annually.
While Ni-Cd never became widely used as a replacement for lead-acid batteries
in the areas where those batteries dominate, up until the mid 1990s, Ni-Cds
had an overwhelming majority of the market share for rechargeable batteries
in consumer electronics.
5) Nickel-Metal Hydride:
Recently, Nickel-Metal Hydride (Ni-MH) and lithium ion batteries
(Li-ion) have become more commercially available and cheaper, though still
more expensive than Ni-Cds. Where energy density is important, Ni-Cds
batteries are at a distinct disadvantage over Ni-MH and Li-ion batteries,
especially when the cost of the battery is small compared to the cost of the
device, such as in cell phones.
6 Battery Characteristics:
6.1 Comparison to Other Batteries:
6.1.1) Advantages:
When compared to other forms of rechargeable battery, the nickel
cadmium battery has a number of distinct advantages.
The batteries are more difficult to damage than other batteries,
tolerating deep discharge for long periods. In fact, NiCd batteries in
long-term storage are typically stored fully discharged. This is in contrast,
for example, to lithium ion batteries, which are highly volatile and will be
permanently damaged if discharged below a minimum voltage. In addition, NiCd
batteries typically last longer, in terms of number of charge/discharge
cycles, than other rechargeable batteries, and have faster charge and
discharge rates than lead-acid batteries, with minimal loss of capacity even
at high discharge rates.
The most common alternative to NiCd batteries are lead-acid batteries.
Compared to these, NiCd batteries have a much higher energy density. This
means that, for a given battery capacity, a NiCd battery is smaller and
lighter than a comparable lead-acid battery. In cases where size and weight
are important considerations (for example, some transportation applications),
NiCd batteries are preferred over the cheaper lead-acid batteries.
In consumer applications, NiCd batteries compete directly with
alkaline batteries. A NiCd cell has a lower capacity than that of an
equivalent alkaline cell, and costs slightly more. However, since the
alkaline battery's chemical reaction is typically not reversible, a reusable
NiCd battery has a significantly longer total lifetime. There have been
attempts to create rechargeable alkaline batteries, such as Rayovac's
rechargeable alkaline, Renewal, or specialized alkaline battery chargers, but
none that has seen wide usage. In addition, a NiCd battery maintains a
constant voltage as it discharges. Since an alkaline battery's voltage drops
as the charge drops, most consumer applications are well equipped to deal
with the slightly lower NiCd voltage with no noticeable loss of performance.
Nickel metal hydride (NiMH) batteries are the newest, and most similar,
competitor to NiCd batteries. Compared to NiCd, NiMH batteries have a higher
capacity and are less toxic, but are still slightly more expensive. In
addition, a NiCd battery has a lower self-discharge rate (for example, 20%
per month for a NiCd, versus 30% per month for a NiMH under identical
conditions). This results in a preference for NiCd over NiMH in applications
where the current draw on the battery is lower than the battery's own
self-discharge rate (for example, television remote controls) In both types
of cell, the self-discharge rate is highest for a full charge state and drops
off somewhat for lower charge states. In addition, like alkaline batteries,
NiMH batteries experience a voltage drop as it nears full discharge, which a
NiCd does not. Finally, a similarly-sized NiCd battery has a slightly lower
internal resistance, and thus can achieve a higher maximum discharge rate
(which can be important for applications such as power tools).
6.1.2) Disadvantages:
The primary trade-off with NiCd batteries is their higher cost and
the extreme toxicity of cadmium. They require extra labor to manufacture, and
thus, are typically more costly than lead-acid batteries. Typically nickel
and cadmium are more costly materials than those used for lead-acid cells.
Another disadvantage of NiCds is that certain usage patterns may cause a
"false bottom" effect. Specifically, if the battery is consistently discharged
to the same level, then fully recharged, the battery will eventually stop
discharging on its own upon reaching this threshold. (See Memory and lazy
battery effects below for more details on this effect). One of the NiCd's
biggest disadvantages was that the battery exhibited a very marked negative
temperature coefficient. This meant that as the cell temperature rose, the
internal resistance fell. Thus could pose considerable charging problems
particularly with the relatively simple charging systems employed for
lead-acid type batteries. Whilst lead-acid batteries could be charged by
simply connecting a dynamo to it, with a simple electromagnetic cut out
system for when the dynamo is stationary, or an over current occurs, the
nickel-cadmium under a similar charging scheme would exhibit thermal runaway,
where the charging current would continue to rise until the over current cut
out operated or the battery destroyed itself. This was the principal factor
that prevented its use for engine starting batteries. Today with alternator
based charging systems with solid state regulators, the construction of a
suitable charging system would be relatively simple, but the car manufacturers
are reluctant to abandon tried and tested technology. In any event, NiCd
technology is falling out of favour.
6.2) Availability:
NiCd cells are available in the same general purpose physical sizes
as alkaline batteries, from AAA through D, as well as several multi-cell
sizes, including the equivalent of a 9 volt battery. Each cell has a nominal
potential of 1.2V, compared to the nominal 1.5V potential for alkaline
batteries. More specifically, a fully charged single NiCd cell, under no load,
carries a potential difference of between 1.25 and 1.35 volts, which stays
relatively constant as the battery is discharged. Since an alkaline battery
near fully discharged may see its voltage drop to as low as 0.9V, NiCd cells
and alkaline cells are typically interchangeable for most applications.
Miniature button cells are sometimes used in photographic equipment,
hand held lamps (flashlight or torch), computer memory standby, toys, and
novelties. In addition to single cells, batteries exist that contain up to
300 cells (nominally 360 volts, actual voltage under no load between 380 and
420 volts). This many cells are mostly used in automotive and heavy duty
industrial applications. For portable applications, the number of cells is
normally below 18 cells (24 V). Industrial-sized flooded batteries are
available with capacities ranging from 12.5Ah up to several hundred Ah.
End part 1 of 2
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บ Compilled from Wikipedia.com . Translatted to ASCII by LW1DSE Osvaldo บ
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บ September 01, 2008 บ
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