Electrical 2.1

7/28/2019 Electrical 2.1

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ELECTRICAL SCIENCE Module 3 DC Circuits

INDUCTANCE

Experiments investigating the unique behavioral features of inductance led to the

invention of the transformer.

EO 1.1 DESCRIBE how magnetic field, current flow, and stored energy in an

inductor associated to one another.

EO 1.2 DESCRIBE how an inductor opposes a modification in current flow.

EO 1.3 Given a circuit containing inductors and CALCULATE total inductance

for series and parallel circuits.

EO 1.4 Given an inductive resistive circuit CALCULATES the time constant for

the circuit.

Inductors

An inductor is a circuit element which will store electrical energy in the form of a

magnetic field. It is commonly a coil of wire wrapped around a core of permeable

material. A magnetic field is generated whenever current is flowing by the wire.

If two circuits are arranged as in Figure, a magnetic field is produced around

Wire A, but there is no EMF (electromotive force) induced into Wire B

since there is no associative motion among the magnetic field and Wire B.

the current stops flowing in Wire A If we now open the switch, and the

magnetic field collapses. As the field collapses, it moves associative to Wire B.

Whenever this occurs, an EMF is induced in Wire B.


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Figure: Induced EMF

This is an instance of Faradays Law that begins in which a voltage is induced in a

conductor whenever that conductor is moved by a magnetic field, or whenever the

magnetic field moves past the conductor. While the EMF is induced within Wire

B, the current will flow whose magnetic field opposes the modify in the

magnetic field which produced it.

For this purpose, an induced EMF is sometimes known as counter EMF or

CEMF. This is an instance of Lenzs Law that states which the induced EMF opposes

the EMF which caused it.

The three needs for inducing an EMF are:

1. A conductor,

2. A magnetic field, and

3. Relative motion between the two.

The faster the conductor moves, or the faster the magnetic field collapses or expands,

the greater Coils the induced EMF. An induction could also be increased by coiling

the wire in either Circuit A or Circuit B, or both, as display in next Figure.


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Figure: Induced EMF in

Self-induced EMF is another phenomenon of induction. The circuit shown in Figure

holds a coil of wire known as an inductor (L). As current flows by the circuit, a

large magnetic field is set up around the coil. Because the current is not changing,

there is no EMF produced. The field around the inductor collapses if we open the

switch. This collapsing magnetic field generates a voltage within the coil. This is

known as self-induced EMF.

Figure: Self-Induced EMF

The polarity of self-induced EMF is provided to us through Lenzs Law. The

polarity is in the direction which opposes the modification in the magnetic field

which induced the EMF. The result is in which the current caused through the

induced EMF tends to manage the similar current which existed in the circuit

before the switch was opened. It is generally said in which an inductor tends to

oppose a change in current flow.

The counter EMF or induced EMF, is proportional to the time rate of change of the

current. The proportionality constant is known as the "inductance" (L). An

Inductance is a measure of an inductors ability to induce CEMF. That is measured

in henries (H). An inductor has an inductance of one henry if one amp per second

modify in current generates one volt of CEMF, as display in Equation (3-1).


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CEMF = -L (I/t) (3-1)

where

CEMF = induced voltage (volts)

L = inductance (henries)

I/t = time rate of change of current (amp/sec)

The minus sign displays in which the CEMF is opposite in polarity to the applied

voltage.

Example: A 4-henry inductor is in series along with a variable resistor. The

resistance is increased so in which the current drops from 6 amps to 2 amps in 2

seconds. What is the CEMF induced?

CEMF = -L (I/t)

= -4(2A-6A/2)

= -4(-2)

CEMF = +8 volts

Figure: Inductors in Series

Inductors in series are combined like resistors in series. Equivalent inductance (Leq)

of two inductors in series that was shown in the Figure is given through Equation (3-

2).

Leq = L1 + L2 + ... Ln (3-2)

Inductors within parallel are combined like resistors in parallel as given by Equation

(3-3).

1/ Leq = 1/ L1 + 1/ L2 +1/LN (3-3)

While only two inductors are in parallel, as display in Figure, Equation (3-3) might

be simplified as provided in Equation (3-4). As display in Equation (3-4), this is

valid when there are only two inductors in parallel.


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Figure: Inductors in Parallel

1/ Leq = L1 L2 / L1 + L2 (3-4)

Inductors will store energy in the form of a magnetic field. A Circuit holding

inductors will behave differently from an easy resistance circuit. Within circuits

with elements which store energy, it is general for current and voltage to exhibit

exponential increase and decay shown in the Figure.

Figure: DC Current through an Inductor

The relationship among values of current reached and the time it takes to reach them

is known as a time constant. A time constant for an inductor is declared as the time

needed for the current either to increase to 63.2 % of its maximum value or to

decrease through 63.2 % of its maximum value that was display in the Figure.


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Figure: Time Constant

The value of the time constant is directly proportional to the inductance and

inversely proportional to the resistance. The time constant can be found using

Equation (3-5) if these two values are known.

TL = L/R (3-5)

where

TL = time constant (seconds)


R = resistance (ohms)

A voltage drop across an inductor is directly proportional to the product of the

inductance and the time rate of modification of current by the inductor, as display in

Equation (3-6).

VL = L ( I/t) (3-6)

where

VL = voltage drop across the inductor (volts)


(I/t) = time rate of change of current (amp/sec)


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After five time constants, circuit parameters generally reach their last value. Circuits

which hold both resistors and inductors are known as RL circuits. The subsequent

example will demonstrate how an RL circuit reacts to modify in the circuit that was

show in the Figure.

1. Initially, the switch is in Position 1, and no current flows by the inductor.

2. Whenever we move the switch to Position 2, a battery attempts to force a

current of 10v/100 = 0.1A by the inductor. Other than as current starts to flow, the

inductor produced a magnetic field. As the field raise a counter EMF is induced

which opposes the battery voltage. Like a steady state is reached, a counter EMF

goes to zero exponentially.

3. Whenever the switch is returned to Position 1 in the magnetic field collapses,

inducing an EMF which tends to manage current flow in the similar direction by theinductor. Its polarity will be opposite to which induced when the switch was

placed in Position 2.

Figure: Voltage Applied to an Inductor

The example which follows displays how a circuit along with an inductor in parallel

within a resistor reacts to modification in the circuit. Inductors have a few small


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resistances, and this is display schematically as a 1 resistor that was display in the

Figure.

1. Although the switch is closed, a current of 20 v/1 = 20 amps flows

by the inductor. This causes an extremely huge magnetic field around the inductor.

2. While we open the switch, there is no longer a current by the inductor. As the

magnetic field starts to collapse, a voltage is induced in the inductor. The

modification in applied voltage is instantaneous; the counter EMF is of exactly the

right magnitude to avoid the current from changing initially. In sequence to manage

the current at 20 amps flowing by the inductor, the self-induced voltage

in the inductor must be enough to push 20 amps through the 101 of resistance.

The CEMF = (101) (20) = 2020 volts.

3. Along with the switch open, the circuit looks like a series RL circuit without abattery. A CEMF induced falls off, as does the current, within a time constant TL of:

Figure: Inductor and Resistor in Parallel

TL = L/R

TL= 4H/101 =0.039 sec


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CAPACITANCE

As of the effect of capacitance, an electrical circuit could store energy, even after

being de-energized.

EO 1.5DESCRIBE the construction of a capacitor.

EO 1.6DESCRIBE how a capacitor stores energy.

EO 1.7DESCRIBE how a capacitor opposes a change in voltage.

EO 1.8Given a circuit holding capacitors, CALCULATE total capacitance for series

and parallel circuits.

EO 1.9Given a circuit holding resistors and capacitors, CALCULATE the time

constant of the circuit.

Capacitor

Electrical devices which are constructed of two metal plates separated through an

insulating material, known as a dielectric, are known as capacitors that are display in

the Figure. The Schematic symbols display in Figures for apply to all capacitors.

Figure: Capacitor and Symbols

The two conductor plates of the capacitor, display in Figure, are electrically neutral,

because there are as several positive as negative charges on every plate. The

capacitor, thus, has no charge.

Now, we connect a battery across the plates. While the switch is closed the negative

charges on Plate A are attracted to the positive side of the battery, although the

positive charges on Plate B are attracted to the negative side of the battery. That


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movement of charges will be continuing until the difference in charge among Plate A

and Plate B is equivalent to the voltage of the battery. That is now a

Figure: Charging a Capacitor

"charged capacitor." Capacitors store energy as an electric field among the two

plates.

Since very few of the charges could cross among the plates, the capacitor will

remain in the charged state even if the battery is removed. Since the charges on the

opposing plates are attracted through one another, they will tend to oppose any

changes in charge. Within this manner, a capacitor will oppose any modification

in voltage felt across it.

Electrons will find a path back to Plate A if we place a conductor across the plates,

and the charges will be neutralized again. This is now a "discharged" capacitor that

was show in the Figure.

Figure: Discharging a Capacitor

Capacitance


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Capacitance is the ability to store an electrical charge. A Capacitance is equal to the

amount of charge which could be stored divided through the applied voltage, as

display in Equation (3-7).

C = Q/ V (3-7)

where

C = capacitance (F)

Q = amount of charge (C)

V = voltage (V)

The unit of capacitance is the F (farad). A farad is the capacitance which will store

one coulomb of charge whenever one volt is applied across the plates of thecapacitor.

The dielectric constant (K) declares the ability of the dielectric to store electrical

energy. Air is used as a reference and is provided a dielectric constant of 1. Thus,

the dielectric constant is unitless. A few other dielectric materials are paper, teflon,

mica, bakelite, and ceramic.

A capacitance of a capacitor depends on three things.

1. Area of conductor plates

2. Separation between the plates

3. Dielectric constant of insulation material

In the Equation (3-8) describe the formula to search the capacitance of a capacitor

along with two parallel plates.

C = K (A/d) (8.85 x 10-12) (3-8)

where

C = capacitance

K = dielectric constant

A = area

d = distance among the plates

8.85 x 10-12 = constant of proportionality


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Example 1: Find the capacitance of a capacitor that stores 8 C of charge at 4 V.

C =Q/ V

C = 8/4

C =2F

Example 2: What is the charge taken on by a 5F capacitor at 2 volts?

Q = C V

Q = (5F) (2V)

Q = 10C

Example 3: What is the capacitance if the area of a two plate mica capacitor is0.0050 m2 and the separation between the plates is 0.04 m? The dielectric constant

for mica is 7.

C = K (A/d) (8.85 x 10 12)

C = 7 (0.0050/0.04) (8.85 x 10 12)

C = 7.74 x 10 12F

C = 7.74 pF

Types of Capacitors

All commercial capacitors are named according to their dielectrics. The most general

are air, paper, mica, and ceramic capacitors, plus the electrolytic type. These

categories of capacitors are compared in Table 1.


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Capacitors in Series and Parallel

Capacitors in series are combined like resistors in parallel. The total capacitance,

CT, of capacitors connected in series Figure, is shown in Equation (3-9).

Figure: Capacitors Connected in Series

1/CT =1/C1 +1/C2 +1/C3+1/CN (3-9)

While only two capacitors are in series in the Equation (3-9) might be simplified as

provide in Equation (3-10). As display in Equation (3-10), this is valid whenever

there are only two capacitors in series.

CT =C1 C2/ C1+C2

While all the capacitors in series are the similar value, the total capacitance could be

found through dividing the capacitors value through the number of capacitors in

series as provided in Equation (3-11).

CT = C/ N

where


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C = value of any capacitor in series

N = denotes number of capacitors in series along with the similar value.

Capacitors in parallel are combined such as resistors in series. Whenever capacitors

are connected in parallel that was show in the Figure, the total capacitance, CT, is thesum of the individual capacitances as given in Equation (3-12).

CT = C1 + C2 + C3 + ... + CN (3-12)

Figure Capacitors Connected in Parallel

Example 1: Find out the total capacitance of 3F, 6F, and 12F capacitors connected

in series (Figure).

1/CT =1/C1 +1/C2 +1/C3

= 1/3 +1/6 +1/12

=4/12+ 2/12+ 1/12

=7/12

CT =12/7 =1.7 f


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Figure Example 1 Capacitors Connected in Series

Example 2: Find out the total capacitance and working voltage of two capacitors in

series, whenever both have a value of 150 F, 120 V (Figure).

CT= C/N

=150/2

CT =75 fTotal voltage which could be applied across a group of capacitors in sequence is

equal to the sum of the working voltages of the individual capacitors.

working voltage = 120 V + 120 V = 240 volts

Figure Example 2 Capacitors Connected in Series

Example 3: Find the total capacitance of three capacitors in parallel, if the values

are 15 F-50 V, 10 F-100 V, and 3 F-150 V (Figure). What would be the working

voltage?

CT = C1 +C2 +C3

= 15 F+10 F+3 F

CT=28 F

The working voltage of a group of capacitors in parallel is just as high as the lowest

working voltage of an individual capacitor. Thus, the working voltage of this

combination is only 50 volts.


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Figure: Example 3 - Capacitors Connected in Parallel

Capacitive Time Constant

While a capacitor is linked to a DC voltage source, it charges extremely rapidly. The

capacitor would become charged almost instantaneously if no resistance was present

in the charging circuit. A Resistance within a circuit will cause a delay in the time for

charging a capacitor. The exact time needed to charge a capacitor depends on the R

(resistance) and the C (capacitance) in the charging circuit. In the Equation (3-13)

describes this relationship.

TC = RC (3-13)

where

TC = capacitive time constant (sec)

R = resistance (ohms)

C = capacitance (farad)

The capacitive time constant is the time needed for the capacitor to charge to 63.2 %

of its fully charged voltage. Within the following time constants, the capacitor will

charge a further 63.2 % of the remaining voltage. A capacitor is considered fullycharged after a period of five time constants that was show in the Figure.


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Figure Capacitive Time Constant for Charging Capacitor

The capacitive time constant also display which it needed five time constants for the

voltage across a discharging capacitor to drop to its minimum value show in the

Figure.

Figure Capacitive Time Constant for Discharging Capacitor

Example: Find the time constant of a 100 F capacitor in series with a 100

resistor (Figure 20).

TC = RC

TC = (100 ) (100 F)


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TC = 0.01 seconds

Figure Example - Capacitive Time Constant


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ELECTRICAL SCIENCE Module 4 Batteries

BATTERY TERMINOLOGY

Batteries are used for a huge variety of services by technology today. For starts to

study battery operation and features, a few terms which are used within batteries

must be understood.

EO 1.1 DEFINE the following terms as they associate to batteries and voltaic

cells:

a. Voltaic cell

b. Battery

c. Electrode

d. Electrolyte

e. Specific gravity

f. Ampere-Hour

Voltaic Cell

The word voltaic cell is declared as a combination of materials used to convertchemical energy into electrical energy. The voltaic or chemical cell consists of two

electrodes made of various categories of metals or metallic compounds placed in an

electrolyte solution.

Battery

A battery is a group of two or more linked voltaic cells.

Electrode

An electrode is a metallic compound or a metal that has an abundance of electrons

(negative electrode) or an abundance of positive charges (positive electrode).

Electrolyte

An electrolyte is a solution that is capable of conducting an electric current. The

electrolyte of a cell might be a liquid or a paste. The cell is referred to as a dry cell if

the electrolyte is a paste; it is called a wet cell if the electrolyte is a solution.

Specific Gravity


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Specific gravity is declared as the ratio comparing the weight of some liquid to the

weight of an equal volume of water. A specific gravity of pure water is 1.000. Lead-

acid batteries use an electrolyte that holds sulfuric acid. Pure sulfuric acid has a

specific gravity of 1.835, since it weighs 1.835 times as much as pure water per unit

volume.

Since the electrolyte of a lead-acid battery consists of a mixture of water and sulfuric

acid, the specific gravity of the electrolyte will fall between 1.000 and 1.835.

Normally, the electrolyte for a battery is mixed such that the specific gravity is less

than 1.350.

Specific gravity is measured with a hydrometer. A simple hydrometer consists of a

glass float inside a glass tube, as shown in Figure 1. The hydrometer float is

weighted at one end and sealed at both ends. A scale calibrated in specific

gravity is positioned lengthwise along the body of the float. The float is placed inside

the glass tube, and the fluid to be tested is drawn into the tube. As the fluid is

drawn into the tube, the hydrometer float will sink to a certain level in the fluid.

The extent to which the hydrometer float protrudes above the level of the fluid

depends on the specific gravity of the fluid. The reading on the float scale at the

surface of the fluid is the specific gravity of the fluid.

Ampere-Hour

An ampere-hour is defined as a current of one ampere flowing for one hour. If youmultiply the current in amperes by the time of flow in hours, the result is the total

number of ampere-hours. Ampere- hours are normally used to indicate the amount

of energy a storage battery can deliver.


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Figure Simple Hydrometer


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Figure Basic Chemical Production of Electrical Power

This action causes electrons to be erased from the copper electrode, leaving it along

with an excess of positive charge. The forces of attraction and repulsion will cause

the free electrons in the negative zinc electrode to move by the connecting wire

and load if a load is connected across the electrodes, and toward the positive

copper electrode that was show in the Figure.

The potential difference which results permits the cell to function as a source of

applied voltage.

Figure Electron Flow Through a Battery


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Discharge and Charging of Lead-Acid Battery

Within a lead-acid battery, two categories of lead are acted upon electro-chemically

through an electrolytic solution of diluted sulfuric acid (H2SO4). A positive plate

consists of lead peroxide (PbO2) and the negative plate is sponge lead (Pb), display

in Figure.

Figure Chemical Actions during Discharge

Whenever a lead-acid battery is discharged, the electrolyte divides within H2 and

SO4. The H2 will combine with some of the oxygen that is formed on the positive

plate to generate water (H2O), and thus decrease the amount of acid in the

electrolyte. The sulfate (SO4) combines with the lead (Pb) of both plates, forming

lead sulphate (PbSO4), as display in Equation (4-1).

PbO2 + Pb + 2H2SO4 discharge 2PbSO4 + 2H2O (4-1)

As a lead-acid battery is charged in the reverse direction, the action declared within

the discharge is reversed. The lead sulphate (PbSO4) is driven out and back into the

electrolyte (H2SO4). A return of acid to the electrolyte will reduce the sulphate in

the plates and increase the specific gravity. That will continue to happen until all of

the acid is driven from the plates and back into the electrolyte, as display in

Equation (4-2) and Figure.


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Figure 5 Chemical Actions during Charging

charge

PbO2 +Pb +2H2SO4 2PbSO4 + 2H2O (4-2)

As a lead-acid battery charge nears finishing, hydrogen (H2) gas is liberated at the

negative plate, and oxygen (O2) gas is liberated at the positive plate. That actionoccurs because the charging current is commonly greater than the current necessary

to decrease the remaining amount of lead sulfate on the plates. The excess current

ionizes the water (H2O) in the electrolyte. Because hydrogen is highly explosive, it is

necessary to gives adequate ventilation to the battery whenever charging is in

progress. Also, electric sparks, no smoking, or open flames are permitted near a

charging battery.

The reduction in specific gravity on discharge is proportional to the ampere-hours

discharged. Although charging a lead-acid battery, the rise within specific gravity isnot proportional or uniform, to the amount of ampere-hours charged that was show

in the below Figure.


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Figure Voltage and Specific Gravity During Charge and Discharge

The electrolyte in a lead-acid battery plays a direct role in the chemical reaction. The

specific gravity reduces as the battery discharges and rise to its normal, real value as

it is charged. Because specific gravity of a lead-acid battery reduces proportionally

during discharge, the value of specific gravity at some provided time is an

approximate denotes of the batterys state of charge. For determine the state of

charge, compare the specific gravity, as read by using a hydrometer, along with thefull charge value and the manufacturers published specific gravity drop that is the

reduction from full to nominal charge value.

Example: A lead-acid battery reads 1.175 specific gravity. Their average full

charge specific gravity is 1.260 and has a normal gravity dropped of 120 points

(or.120) at an 8 hour discharge rate.

Solution:

Fully charged - 1.260

Present charge - 1.175

The battery is 85 points below its fully charged state. It is thus about 85/120, or 71

percent, discharged.


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BATTERY OPERATIONS

Once a general theory behind the operation of batteries is understood, we could

apply these concepts to better know the way batteries are utilized.

EO 1.6DESCRIBE the relationship among total cell voltage and battery voltage for a

series-connected battery.

EO 1.7STATE the benefits of connecting a battery in parallel along with respect to

current-carrying capability.

EO 1.8 STATE the difference among primary and secondary cells within respect to

recharge capability.

Series Cells

When various cells are linked in series as like in the Figure, the total voltage output

of the battery is equal to the sum of the individual cell voltages. In the instance of

the battery in Figure, the four 1.5V cells give a total of 6 volts. Whenever we

connect cells in series, the positive terminal of one cell is linked to the negative

terminal of the next cell. The current flow by a battery connected in series is the

similar as for one cell.

Figure 7 Cells Connected in Series


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Parallel Cells

Cells linked in parallel show in the Figure, provide the battery a greater current

capacity. Whenever cells are linked in parallel, all the positive terminals are

connected together and whole the negative terminals are connected together. The

total voltage outcome of a battery connected in parallel is the similar as in which of a

single cell. Cells connected in parallel have the similar effect as increasing the size of

the electrodes and electrolyte in a single cell. The benefits of connecting cells in

parallel are which it will raise the current-carrying capability of the battery.

Figure Cells Connected in Parallel

Primary Cell

Cells which cannot be returned to good recharged or condition after their voltage

outcome has dropped to a value which is not usable, are known as primary cells.

Dry cells which are used in flashlights and transistor radios example for AA cells, Ccells are instances of primary cells.

Secondary Cells

Cells which could be recharged to nearly their original condition are known as

secondary cells. The most general instances of a secondary and rechargeable cell, is

the lead-acid automobile battery.


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Capacity

The capacity of a storage battery determines how long the storage battery will

operate at a certain discharge rate and is rated in ampere-hours. For instance, a 120

ampere-hour battery have to be recharged after 12 hours if the discharge rate is 10

amps.

Internal Resistance

Internal resistance in a chemical cell is due commonly to the resistance of the

electrolyte among electrodes in the Figure.

Any current in the battery have to flow by the internal resistance. The internal

resistance is in series along with the voltage of the battery, causing an internal

voltage drop show in the Figure.Along With no current flow, the voltage drop is zero; therefore, the full battery

voltage is established across the output terminals (VB). Load resistance (RL) is in

series with internal resistance (Ri) if a load is placed on the battery.

Figure Internal Resistance in a Chemical Cell

Figure Internal Voltage Drop


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Whenever current flows in the circuit (IL) than the internal voltage drop (ILRi) drops

the terminal voltage of the battery as shown in Equation (4-3). Thus, internal

resistance decreases the current and voltage both available to the load.

VL = VB - ILRi (4-3)

Shelf Life

The shelf life of a battery is the time that a battery might be stored and not lose more

than 10 % of its original capacity.

Charge and Discharge

The charge of a battery might refer to as one of two things: (1) the associative state

of capacity of the battery, or (2) the fact act of applying current flow within the

reverse direction to return the battery to a fully-charged state.

Discharge, simply begins, is the act of drawing current from a battery.


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TYPES OF BATTERIES

The lead-acid battery is the most general categories of battery in use today. There

are other categories of storage batteries, each of them having certain benefits.

EO 1.9 STATE the benefits of each of the following categories of batteries:

a. Carbon-zinc cell

b. Alkaline cell

c. Nickel-cadmium cell

d. Edison cell

e. Mercury cell

Wet and Dry Cells

Wet and dry cells are categorized through the type of electrolyte the battery uses.

The electrolyte of a cell might be a liquid or a paste. The cell is referred to as a dry

cell if the electrolyte is a paste. The cell is known as a wet cell if the electrolyte is a

solution.

Carbon-Zinc Cell

The carbon-zinc cell is one of the oldest and most hugely used types of dry cells. The

carbon in the battery is in the form of a rod in the middle of the cell that acts as the

positive terminal. The case is made from zinc and acts as the negative electrode. The

electrolyte for this category of cell is a chemical paste-like mixture that is housed

among the carbon electrode and the zinc case. The cell is then sealed to avoid any of

the liquid in the paste from evaporating.

The benefits of a carbon-zinc battery are in which it is durable and extremely

inexpensive to generate. The cell voltage for these categories of cell is about 1.5

volts.

Alkaline Cell

The alkaline cell is so known as since it has an alkaline electrolyte of potassium

hydroxide. A negative electrode is made from zinc, and the positive electrode is

made of manganese dioxide. The classical alkaline cell produces 1.5 volts. The

alkaline cell has the benefits of an extended life over which of a carbon-zinc cell of

the similar size; therefore, it is commonly more expensive.


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Nickel-Cadmium Cell

The nickel-cadmium cell is a secondary cell and the electrolyte is potassium

hydroxide. A negative electrode is creating of nickel hydroxide and the positive

electrode is creating of cadmium hydroxide. A nominal voltage of a nickel-cadmium

cell is 1.25 volts. It has the benefits of being a dry cell which is a true storage battery

along with a reversible chemical reaction that is it could be recharged. The nickel-

cadmium battery is a rugged and dependable battery. It provides dependable

service under extreme conditions of shock, temperature, and vibration. It is

ideally suited for use in portable communications equipment due to its

dependability.

Edison Cell

Within an edison cell the positive plate consists of nickel hydrate and nickel, and thenegative plate is made of iron. An electrolyte is an alkaline. Classical voltage output

is 1.4 volts, and it should be recharged whenever it reaches 1.0 volts. The edison cell

has the benefits of being a lighter and more rugged secondary cell than a lead-acid

storage battery.

Mercury Cell

Mercury cells come in two categories; one is a flat cell which is shaped such as a

button, although the other is a cylindrical cell which is looks like a regular

flashlight battery. Every cell produces about 1.35 volts. These cells are extremely

rugged and have an associatively long shelf life. The mercury cell has the benefits of

maintaining a fairly constant output under varying load conditions. By this reason,

they are used in products like as cameras, hearing aids, electric watches and test

instruments.


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BATTERY HAZARDS

Because batteries store huge amounts of energy, there are certain hazards which are

related along with battery operation. These hazards must be fully understood to

ensure safe operation of batteries.

EO 1.10 EXPLAIN the adverse effects of a shorted cell.

EO 1.11 EXPLAIN how gas generation is minimized for a lead-acid battery.

EO 1.12 EXPLAIN how heat is produced in a lead-acid battery.

Shorted Cell

Cell short circuits could be caused through various conditions that involve the

following: faulty separators; other metals forming or lead particles a circuit among

the negative and positive plates; buckling of the plates; or excessive sediments in the

bottom of the jar. The main cause of some of these occurrences is overcharging and

over discharging of the battery that causes sediment to build up due to flaking of

active buckling and material of cell plates.

Overcharging and over discharging should be prevented at all costs. Short circuits

cause a wide reduction in battery capacity. Along with every shorted cell, battery

capacity is decrease through a percentage equal to one over the total number of cells.

Gas Generation

A lead-acid battery cannot absorb all the energy from the charging source whenever

the battery is nearing the completion of the charge. This excess energy dissociates

water through way of electrolysis into oxygen and hydrogen. Oxygen is generates

through the positive plate, and hydrogen is produced through the negative plate.

This procedure is known as gassing.

Gassing is first remember when cell voltage reaches 2.30-2.35 volts per cell and

increases as the charge progresses. At full charge, the amount of hydrogen generates

is about one cubic foot per cell for each 63 ampere-hours input. An explosive

mixture of hydrogen and oxygen can be readily produced if gassing occurs and the

gases are prevents to collect. It is necessary, thus, to ensure in which the area is well

ventilated and in which it remains free of any open flames or spark- producing

equipment.

As long as battery voltage is greater than 2.30 volts per cell, gassing will occur and

cannot be prevented entirely. To decrease the amount of gassing, charging voltages

above 2.30 volts per cell should be minimized example for 13.8 volts for a 12 voltbattery.


34/34

Battery Temperature

The operating temperature of a battery should preferably to be maintained within

the nominal band of 60-80F. Every time the battery is charged, a current flowing by

the battery will cause heat to be produced through the electrolysis of water. The

current flowing by the battery (I) will also cause heat to be produce (P) during

charge and discharge as it passes by the internal resistance (R i), as describes using

the formula for power in Equation (4-4).

P = I2Ri (4-4)

Higher temperatures will provide a few additional capacities, but they will

eventually decrease the life of the battery. Extremely high temperatures, 125F and

higher, could actually do damage to the battery and cause early failure.

Low temperatures will lower battery capacity but also prolong battery life under

floating that is slightly charging operation or storage. Very low temperatures could

freeze the electrolyte other than only if the battery is low in specific gravity.

Electrical 2.1

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