nickel cad batteries

8/3/2019 Nickel Cad Batteries

1/34

ELECTRIC CIRCUITS


2/34

ELECTRIC CIRCUITS

INTRODUCTION OF Ni-Cd

BATTERIES Nickel-cadmium cells have an anode

(negative) in cadmium hydroxide and a

cathode (positive) in nickel hydroxide,immersed in alkaline solution

(electrolyte) comprising potassium,

sodium and lithium hydroxides. The

cells are rechargeable and deliver a

voltage of 1.2 V during discharge.


3/34

ELECTRIC CIRCUITS

Types of Ni-Cd batteries


4/34

ELECTRIC CIRCUITS

AMPERE- HOUR RATING FOR

BATTERIES An ampere-houroramp-

hour(symbol Ah , Ah, A h) is a unitofelectric charge, with sub units milli-

ampere-hour(mAh) and milli-amperesecond (mAs).

One ampere-hour is equal to

3,600coulombs (ampere-seconds), theelectric charge transferred by a steadycurrent of one ampere for one hour.


5/34

ELECTRIC CIRCUITS

The ampere-hour is frequently used in

measurements ofelectrochemical systems

such as electroplating and electricalbatteries.

The commonly seen milliampere-hour (mAh

or mAh) is one-thousandth of an ampere-

hour (3.6 coulombs).

A milliampere second (mAs) is a unit of

measure used in X-ray diagnostic imaging

and radiation therapy.


6/34

ELECTRIC CIRCUITS

This quantity is proportional to the total X-

ray energy produced by a given X-ray tube

operated at a particular voltage.

The same total dose can be delivered in

different time periods depending on the X-

ray tube current. The Faraday constant is the charge on

one mole of electrons; approximately

equal to 26.8 ampere-hours. It is used inelectrochemical calculations.

An ampere-hour is not a unit ofenergy.


7/34

ELECTRIC CIRCUITS

In a battery system, for example, accuratecalculation of the energy delivered

requires integration of the power delivered(product of instantaneous voltage andinstantaneous current) over the dischargeinterval.

Generally, the battery voltage variesduring discharge; an average value maybe used to approximate the integration ofpower.

In summary, the higher the mAh, thelonger the battery will last.


8/34

ELECTRIC CIRCUITS

CHARACTERSTICS OF Ni-Cd

BATTERIES 1.2 Volt secondary cells using an alkalinechemistry with energy density about doublethat of lead acid batteries.

They use nickel hydroxide Ni (OH) 2 for thepositive electrode (cathode), cadmium Cd asthe negative electrode (anode) and analkaline potassium hydroxide KOHelectrolyte.

The cells are sealed and utilize arecombinant system to prevent electrolyteloss and extend the useful life.


9/34

ELECTRIC CIRCUITS

They use nickel hydroxide Ni (OH) 2 for the

positive electrode (cathode), cadmium Cd as

the negative electrode (anode) and analkaline potassium hydroxide KOH

electrolyte.

Once the battery of choice for low power

portable products they have lost market

share to the newerNickel Metal Hydride and

Lithium batteries.

Open cells are prismatic in shape, withcasing in plastic (possibly flame retardant) or

stainless steel or nickel steel.


10/34

ELECTRIC CIRCUITS

APPLICATIONS OF Ni-Cd

BATTERIES Motorized equipment

Power tools

Two way radios

Electric razors

Commercial and industrial portableproducts

Medical instrumentation Emergency lighting

Toys


11/34

ELECTRIC CIRCUITS

ADVANTAGES OF Ni-Cd

BATTERIES Low internal resistance (less than half

the equivalent NiMH cells).

High rate charge and discharge ratespossible.

Up to 10C discharge rates for short

periods typical. Flat discharge characteristic (but falls

off rapidly at the end of the cycle) .


12/34

ELECTRIC CIRCUITS

Flat discharge characteristic (but falls

off rapidly at the end of the cycle).

Tolerates deep discharges - can be deep

cycled.

Wide temperature range (Up to 70C). Typical cycle life is over 500 cycles.

Charging process is strongly

endothermic-the battery cools during

charging.


13/34

ELECTRIC CIRCUITS

Rapid charge typically 2 hours, but can be

as low as 10 to 15 minutes.

The columbic efficiency of nickel cadmium

is over 80% for a fast charge but can drop

to below 50% for slow charging.

The sealed nickel-cadmium cell can be

stored in the charged or discharged state

without damage. It can be restored for

service by recharging severalcharge/discharge cycles.


14/34

ELECTRIC CIRCUITS

The electrolyte is commonly available,

low cost potassium hydroxide KOH.

Available in a large variety of sizes and

capacities.

This makes it possible to charge veryquickly, as the I2Rheating and

endothermic chemical reactions

counteract each other.


15/34

ELECTRIC CIRCUITS

SHORTCOMINGS OF Ni-Cd

BATTERIES A major drawback of this technology is its

susceptibility to memory effect.

Originally, the terms memory effect or memory

problem was coined to describe a cyclic memoryproblem where the NiCad battery would

"remember" the amount of discharge for previous

discharges and limit the recharge life of the

battery. The problem is less prevalent withmodern Ni-Cd batteries, which are designed to

avoid cyclic memory issues.


16/34

ELECTRIC CIRCUITS

The memory effect is caused by a change in

crystalline formation from the desirable

small size to a large size which occurs when

a NiCad battery is recharged before it is

fully discharged.

The growth of large crystals increases thecell impedance and can eventually prevent

the battery from discharging beyond that

point and/or cause rapid self-discharge ofthe battery.


17/34

ELECTRIC CIRCUITS

The growth of large crystals can be avoidedby either completely discharging it each

time it is used or by using a NiCad batterycharger which has a built-in dischargecircuit.

Memory effect can sometimes be reversed

by putting the battery through severalcomplete discharge and recharge cycleswhich helps to recover the smaller crystalformations. This is called reconditioning.

NiCad batteries are also prone to damageby overcharging.


18/34

ELECTRIC CIRCUITS

Low cell voltage of 1.2 Volts compared with

primary alkaline cells 1.5 Volts and only quarter

of the capacity of the alkaline cells. Self-re-sealing safety vents must be incorporated

to prevent damage due to overheating and

pressure build up.

Cadmium is a high cost heavy metal and its use inconsumer products is now deprecated on

environmental grounds.

The gradually being phased out in favor ofNickel

metal hydride and which superior energy density

characteristics and performance characteristics.


19/34

ELECTRIC CIRCUITS


20/34

ELECTRIC CIRCUITS

TEMPERATURE

CHARACTERSTICS

"Eveready" sealed nickel-cadmium cellsexperience a relatively small change ofoutput capacity over a wide range of

operating temperature. Charging, however, must be done in a

much narrower range.

Temperature limits applicable to operationof the cells are listed in the specificationsheets for each battery.


21/34

ELECTRIC CIRCUITS

The capacities vs. temperature curves

which are on some individual specification

sheets represent cells discharged at thetemperatures shown after charging at

room temperature for 14 hours at the 10

hour rate . This characteristic is also generalized on

the following curve.

Contd./-


22/34

ELECTRIC CIRCUITS

OPERATION OF SEALED Ni-Cd

BATTERIES

Any secondary cell is a combination of activematerials which can be electrolytic oxidized andreduced repeatedly.

The oxidation of the negative electrode occurringsimultaneously with the reduction of the positivegenerates electric power.

In a rechargeable battery both electrode reactions

are reversible and the input of current in theproper direction from an outside source will drivethe primary or discharge reaction backwards andin effect recharge the electrodes.


23/34

ELECTRIC CIRCUITS

In the uncharged condition the positive

electrode of a nickel-cadmium cell is

nickelous hydroxide, the negative cadmiumhydroxide.

In the charged condition the positive

electrode is nickel hydroxide, the negativemetallic cadmium.

The electrolyte is potassium hydroxide. The

average operating voltage of the cell under

normal discharge conditions is about 1.2

volts.


24/34

ELECTRIC CIRCUITS

The over-all chemical reaction of the nickelcadmium system can be considered as:

(Charged) KOH (Discharged). During the latter part of a recommended

charge cycle and during overcharge, nickel-cadmium batteries generate gas.

Oxygen is generated at the positive (nickel)electrode after it becomes fully charged andhydrogen is formed at the negative(cadmium) electrode when it reaches fullcharge.

Cd + 2NiOOH + 2H2O =Cd (OH) 2 + 2Ni (OH) 2


25/34

ELECTRIC CIRCUITS

DISCHARGING OF BATTERY

HIGH CURRENT PULSE DISCHARGE:-

High rate nickel-cadmium cells will deliverexceedingly high currents.

If they are discharge continuously undershort circuit conditions, self-heating may doirreparable damage.

The heat problems vary somewhat from one

cell type to another, but in most casesinternal metal strip tab connectors overheator the electrolyte boils.


26/34

ELECTRIC CIRCUITS

General overheating is normally easy to

prevent because the outside

temperature of the battery can be usedto indicate when rest, for cooling, is

required.

In terms of cut off temperature duringdischarge, it is acceptable practice to

keep the battery always below

45degreeC (113F).

The overheated internal connectors are

difficult to detect.


27/34

ELECTRIC CIRCUITS

This form of overheating takes place in a few

seconds or less, and overall cell temperature may

hardly be affected. It is thus advisable to withdraw no more ampere

seconds per pulse, and to withdraw it at no greater

average current per complete discharge, than

recommended on the data sheet for the"Eveready" cell in question.

In special cases, where cooling of the cell or

battery is likely to be poor, or unusually good,

special tests should be run to check the importanttemperatures before any duty cycle adjustment is

made.


28/34

ELECTRIC CIRCUITS

Output capacity is any discharge composed ofpulses is difficult to predict accurately becausethere are infinite combinations of current, "on"

time, rest time, and end point voltage. Testing on a specific cycle is the simplest way to

get a positive answer.

The cell is designed so that the oxygen formed inthe positive electrode can reach the metalliccadmium surface of the negative electrode which itoxidizes directly.

Thus, in overcharge, the cadmium electrode isoxidized at a rate just sufficient to offset input

energy, keeping the cell in equilibriumindefinitely.

At this point of equilibrium the positive electrodeis fully charged.


29/34

ELECTRIC CIRCUITS

SELF-DISCHARGE Self-discharge characteristics of Energizer

nickel-cadmium cells are shown in the chart

below.


30/34

ELECTRIC CIRCUITS

CONTINUOUS-OVERCHARGE

The overcharge capability of Energizer cylindricalnickel-cadmium cells is outstanding.

The next chart illustrates initial and subsequent

discharge curves after 2 years continuousovercharge without periodic discharges.

The first discharge after the 2 year charge periodyields a slightly reduced voltage curve and 65%

capacity. The second cycle after 2 years continuous

overcharge provides essentially the samedischarge curve as the initial one.


31/34

ELECTRIC CIRCUITS


32/34

ELECTRIC CIRCUITS


33/34

ELECTRIC CIRCUITS

VARIOUS OTHER BATTERIES


34/34

ELECTRIC CIRCUITS

nickel cad batteries

Documents