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G4WYW > TECH 09.04.08 13:00l 162 Lines 6118 Bytes #999 (0) @ WW
BID : DC0281G4WYW
Read: GUEST
Subj: Charging Nicads part 1 of 4
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Sent: 080409/1013Z @:GB7FCR.#16.GBR.EU #:1551 [Blackpool] FBB-7.03a $:DC0281G4W
From: G4WYW@GB7FCR.#16.GBR.EU
To : TECH@WW
Part 1 of 4
Originally From : G1XOW @ G1XOW.GB7BAD.#23.GBR.EU
Rapid charge controller for Nickel-Cadmium Batteries.
Features :
Uses patented Reflex (R) charging system
Capable of full charge in 20 minutes
Minimizes memory effects
Restores faded capacity
Increases battery life and improves reliability
Improves charge acceptance
Increases charge efficiency
Sophisticated multiple charge termination methods
Insures safe charging
Excessive heating eliminated
Lower internal pressure avoids cell venting
Detects defective cells
The ICS1700 Rapid charge controller is an LSI device using CMOS technology
specifically designed for the intelligent charging of nickel-cadmium
batteries.
The Reflex method allows the safe charging of nickel-cadmium batteries in
as little as 20 minutes.
Alkaline nickel plate technology began with the 1899 invention of a vented
nickel-cadmium battery by Waldmar Jungner. Around the same time Thomas
Eddison
experimented with a rechargeable nickel-iron battery for use in electric
automobiles. Unfortunately, the materials for these alkaline storage
batteries
were expensive in comparison with other types of batteries, so their
practical
use was severely limited.
Since then, several major refinements to Jungner's nickel-cadmium battery
have
dramatically enhanced the characteristics of nickel-cadmium technology. An
improvement in 1932 was a method to place the active materials inside a
porous nickel plate electrode, which was then packed inside a metal tube
container. By 1947, research had begun on the development of a sealed
nickel-
cadmium battery that recombined the internal gases caused by the chemical
reactions instead of venting them. The successful resolution of that
problem
has lead to a wide range of possible uses of nickel-cadmium batteries.
The advantages of sealed nickel-cadmium batteries include excellent
efficiency,
long discharge life, high cycle lifetimes and high energy density in a
small,
lightweight, compact design. Nickel-cadmium batteries are cost effective,
require no maintenance and are very rugged. These attributes continue to
make
these batteries a popular choice for industrial and consumer applications.
BATTERY PARAMETERS.
Batteries are defined as consisting of one or more cells, usually
connected in
series for higher output voltages. Cells are the individual building
blocks
containing a positive cadmium plate, a negative nickel plate, an
insulating
separator and an alkaline electrolyte.
Cell capacity specified as the rate of current a cell can supply over time
under discharge, usually measured in units of ampere-hours. The quality of
reactive materials inside a cell determines the charge a cell can contain;
therefore, the bigger the cell, the more capacity it has.
The parameter for describing current flow is known as the C rate. The C
rate
is defined as the current flow rate that is equal to the battery rated
capacity. For example, applying a 2 ampere charge to a 1 ampere-hour
battery
is a 2C charge rate. The C rate scales with the battery capacity.
The voltage that a nickel-cadmium cell can supply is typically around 1.3
volts
under no-load conditions. The internal electrochemical reactions determine
the
no-load voltage of the cell. The voltage changes slightly with ambient
temperature, age and condition of the cell. The no-load voltage also
varies as
a function of the amount of capacity already removed from the cell.
The effective internal impedance (Zi) is determined by two factors: the
resistance of the internal plates in the cell and the degree of difficulty
of
the ionic flow through the separator and the electrolyte. The resistance
of the
plates is constant; however, the impedance due to the ionic flow varies
dramatically during the application of charge to the cell.
CELL ELECTROCHEMISTRY.
When a cell is charged or discharged the nickel and cadmium plates undergo
an oxidation reduction (redox) reaction. This means oxygen, in an ionized
form,
is transferred between the positive and negative plates.
The redox reaction between the plates occurs without changing the physical
condition of the plates. The reaction is entirely self-contained and
completely
reversible, since the charge or discharge process consumes non of the
active
materials on the plates. While under charge, the positive plate reduces
from
cadmium hydroxide to cadmium by releasing oxygen into the electrolyte and
by
accepting electrons from the charging circuitry.
The alkaline electrolyte in the cell does not undergo a chemical change.
Its
purpose is only to transfer hydroxide ions from one set of plates to the
other.
The oxygen gases that are generated and recombined at the positive and
negative
plates are exothermic reactions. This means that heat is created during
the
reaction. The exothermic heating is a potential problem when charging
nickel-cadmium batteries.
The application of a steady charging current to a discharged battery
causes an
immediate jump in the cell voltage, due to the cells internal impedance.
The
cell voltage continues to rise at a much slower rate as the battery begins
to
accept a charge. In this region the oxygen gas generated by the
electrochemical
reaction is being recombined at the same rate, so the internal cell
temperature
and pressure remains low.
Oxygen and hydrogen are the two gases that are generally present during
cell
charging. Oxygen, which is present in much greater amounts than hydrogen,
causes pressure build-up when more oxygen is created than can be absorbed.
A nominal pressure undercharge of about 1lb/sq.in. will increase rapidly
during
overcharge to 100lbs/sq.in. or higher, depending on the charge rate.
At some time during the charge, the cell voltage begins to rise much more
sharply. This change in slope is caused by an increase in the internal
impedance and signals that the battery is nearing its capacity to accept
charge. The increase in impedance is due to fewer and fewer sites
remaining
on the positive electrode that can generate oxygen.
73 - Mel, G4WYW
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