CHAPTER ONE

INTRODUCTION

1.1 Background of the Study

In this modern society, electricity has great control over the most daily activities

for instance in domestic and industrial utilization of electric power for

operations. Electricity can be generated from public supply to consumers in

different ways including the use of water, wind or steam energy to drive the

turbine as well as more recently the use of gas. Generators, solar energy and

nuclear energy are also source of electricity. In Nigeria, there is inconsistence

supply of electricity by the power supplying company to the consumers. The use

of additional electric power source such as electric power generators and most

recently the use of semiconductor power devices such as the Bipolar Transistor,

Thyristors and particularly MOSFET to generate electric power in conjunction

with a DC battery in few kilowatts are necessary. An Inverter offers a better

additional power source to Generators considering its long duration, cost

effectiveness and maintainability. Inverters are commonly used to supply AC

power from DC sources such as solar panels or rechargeable batteries. (IEEE

Press, 2020) Uninterruptible Voltage supply is an electronic control circuit or

device that is capable of providing a constant output voltage even when there is

variation in load or input voltage as low as 160 volt can be boosted up to 240

volt by stabilizer at output stage without any voltage fluctuation with a backup

1
battery which provide additional power to the device during mains power

outage.

It is designed to meet up with the AC voltage safety, stability and accuracy

demand in industries and in homes. Uninterruptible power supply is useful in

devices such as computer Power supplies, alternators and central power station

generator plants, voltage regulators control the output of the plant. In an electric

power distribution system, voltage regulators may be installed at a substation or

along distribution lines so that all customers receive steady voltage independent

of how much power is drawn from the line.

An uninterruptible power supply is designed to automatically maintain a

constant AC voltage level. An AC Voltage supply may be a simple “feed-

forward” design or may include negative feedback control loops. It makes use

of an electromechanical mechanism, and other electronic components.

Depending on the design, it may be used to regulate one or more AC voltages.

This project is designed to stabilize an AC input voltage of 160-250V to give an

AC output voltage of 240V at 50Hz automatically. The automatic feature can be

achieved by the electronics devices used such voltage comparator IC,

electromagnetic device (relay), auto- transformer and other electronics devices.

Commonly called the UPS, this device is a cleaver threefold package-a set of

battery, an inverter that transforms the low-voltage direct current of the batteries

into the standard alternating current equivalent to your wall outlet, and a battery

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charger that assures that reserve powers to rage system (the batteries) with

interfaces to match it to utility power and your computer system. AUPS differs

from an auxiliary emergency power system or standby generator in that it will

provide instantaneous or near-instantaneous protection from input power

interruptions by means of one or more attached batteries and associated

electronic circuitry for low power users, and or by means of diesel generators

and flywheels for high power users. While not limited to protecting any

particular type of equipment, a UPS is typically used to protect computers, data

centers, telecommunication equipment or other electrical equipment where an

unexpected power disruption could cause injuries, fatalities, serious business

disruption and/or data loss. (Solter, 2022)).

UPS units range in size from units designed to protect a single computer

without a video monitor (around 200VA rating) to large units powering entire

data centers, buildings, or even cities. The UPS is designed to protect against

changes, specifically a temporary loss of electrical supply. This project focuses

on conversion of AC to DC and from DC to AC power inverters, which aim to

efficiently transform a DC power source to a high voltage AC source, similar to

power that would be available at an electrical wall outlet. Inverters are used for

many applications, as in situations where low voltage DC sources such as solar

panels or fuel cell must be converting electrical power from a car battery to run

a laptop, TV or cell phone (Rodriguez, Jose; et al., August 2022).

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 1.2 Statement of the Problem

The primary problem statement for Uninterruptible Power Supplies (UPS)

revolves around ensuring continuous and stable power delivery, particularly in
the face of power outages or fluctuations. UPS systems are designed to mitigate
the negative impacts of utility power failures, such as data loss, hardware
damage, and operational disruptions. This includes addressing issues like
voltage spikes, sags, and noise that can compromise equipment and data.
Here's a more detailed breakdown of the problem statement:
i) Power Outages:
UPS systems are crucial for preventing data loss, system crashes, and damage
to sensitive equipment during power outages.
ii) Power Fluctuations:
UPSs protect against voltage spikes, sags, and other power disturbances that
can damage or damage equipment.
iii) Data Loss and Damage:
Without a UPS, a power outage can lead to unsaved data, corrupted files, and
even physical damage to hardware.
iv) Operational Disruptions:
Power outages disrupt business processes, delay critical tasks, and impact
productivity.
v) Cost and Efficiency:
UPS systems can help minimize the costs associated with data loss, downtime,
and equipment repairs, as well as improve overall operational efficiency.
1.3 Aim and Objective

1.3.1 Aim

The main aim of designing an uninterruptible power supply (UPS) is to provide

a reliable and stable backup power source to critical loads, especially during

power outages or fluctuations. This ensures that sensitive equipment can

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continue operating without interruption and is protected from potential damage

caused by power anomalies like voltage surges or sags.

1.3.2: Objective

The specific objectives include:

i) Design a modified sine wave inverter using a 555 timer as a pulse

generator.

ii) To use two set of transistor array and a high voltage chopper transformer

as a statics switch and output power amplification respectively.

iii) Apply new technologies in the design of a light and cost effective UPS

due to the sizes of transformer and battery involved

iv) To provide additional power automatically at 50Hz using 3.7V or 12V

battery

1.4 Significance of the Study

The main problem in Nigeria within the energy sector recently is the generation

and distribution of electrical power. This situation has been attributed to a local

word known as ‘Epileptic power supply’ meaning excessive fluctuation of

electric power supply.

The main significance of this project is to help solve this epileptic power supply

problem in the country, by providing a prolonged backup system of electrical

power.

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Another problem this project will solve is the pollution of the environment by

generator sets which burns fossil fuel and releases carbon monoxide into the

environment, accompanied by noise.

This problem will be solved because the inverter does not depend on fossil fuel

and does not produce excessive noise, making it environmentally friendly.

1.5 Scope of the Study

The study will cover the design and construction of uninterruptible power

supply. When this system is plugged into the socket or supply, It will receive a

minimum voltage of 220V AC and filter the current and voltage thereby brings

out suitable voltage output to be used by the devices in it, then when there an

unexpected power outage from the utility mains the system will automatically

switch over to the inverter source thereby providing additional power to the

appliances in use thereby reducing the risk and damages the fluctuation caused

by power fluctuations and unexpected power interruption.

Finally, the circuit is designed to produce a maximum of 1000W of power

supply

1.6 Limitation of the Study

The design of uninterruptible power supplies (UPS) faces several limitations,

including runtime constraints due to battery capacity, potential harmonic

distortion from inverter output, and the need to balance cost, size, and

efficiency. Additionally, high-demand environments require larger batteries and

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robust inverters, while switching time and voltage regulation capabilities also

pose challenges. Also its inability to power load beyond 1000W capacity.

1.7 Theoretical background of the study

The theoretical foundation for using uninterruptible power supplies (UPS) stems
from the need to mitigate the detrimental effects of power outages and
fluctuations on critical systems and equipment. UPSs are designed to provide a
temporary, reliable power source, allowing devices to continue operating or
shut down gracefully during power disruptions, thus preventing data loss,
damage, and potential business disruption.
Here's a more detailed look at the theoretical underpinnings:
i. Power Outages and Their Consequences:
Data Loss and Corruption:
Sudden power outages can lead to incomplete data files, corruption of stored
information, and the loss of ongoing work.
Equipment Damage: Unexpected power fluctuations, including surges and
brownouts, can damage sensitive electronic equipment.
Business Disruption: Power outages can cause significant disruptions in
business operations, especially for organizations that rely heavily on
computers and other electronic equipment.
System Failures: Unexpected power interruptions can cause system failures,
particularly in critical systems like those used in hospitals, data centers, and
telecommunications.
ii. UPS as a Solution:
Backup Power Source: A UPS provides a temporary, battery-powered
alternative to the main power source, allowing devices to continue operating
during a power outage.
Data Protection: UPS systems allow for orderly shutdowns, minimizing the
risk of data loss and corruption.
Equipment Protection:
UPS can help prevent damage to sensitive equipment by mitigating power
surges and fluctuations.
Time to Critical Actions:

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UPS provides enough runtime to allow for actions like saving work, shutting
down systems gracefully, or activating alternative power sources like
generators.
iii. UPS Types and their Functions:
Online UPS: Provides continuous power from the battery, offering the highest
level of protection.
Offline UPS: Provides power only when the main power source fails, offering
basic protection.
Line-Interactive UPS: Uses the battery to provide power during fluctuations
or outages, offering a balance between cost and protection.
iv. Benefits of Using a UPS:
Data Integrity: Prevents data loss and corruption during power outages.
Equipment Reliability: Protects equipment from damage caused by power
fluctuations.
Business Continuity: Enables businesses to maintain operations during power
outages.
Peace of Mind: Provides assurance that critical systems will continue to
function during power disruptions.
In summary, the theoretical basis for using a UPS is rooted in the need to
protect sensitive equipment and data from the damaging effects of power
outages and fluctuations. By providing a temporary backup power source, UPS
systems allow for safe shutdowns, data protection, and business continuity,
making them an essential tool for organizations that rely on electrical power for
their operations.

1.8 Definition of Terms

i) Uninterrupted Power Supply (UPS): A device that provides backup power

to electronic equipment during a power failure or when the main power source

becomes unstable. It ensures continuous operation of devices by instantly

supplying power from its internal battery.

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ii) Battery Bank: A group of batteries connected in series or parallel to provide

the necessary power storage for a UPS system. It stores energy for use when the

main power supply is unavailable.

iii) Inverter: An electronic device that converts DC (Direct Current) from the

battery into AC (Alternating Current), which is used to power most electronic

devices. In a UPS, the inverter ensures that the power supplied during an outage

is suitable for the devices being powered.

iv) Rectifier: A component in a UPS system that converts AC power from the

electrical grid into DC power to charge the UPS’s battery bank. It plays a

crucial role in ensuring that the UPS is ready to provide backup power when

needed. v) v) Load Capacity: The total amount of power a UPS system can

support without failure. In this case, the load capacity of the UPS is 1000 watts,

meaning it can power equipment that consumes up to 1000 watts.

vi) Voltage Regulation: The process of maintaining a consistent output voltage

from the UPS, regardless of variations in the input voltage from the main power

source.

This ensures that the connected equipment receives stable power.

Vii) Surge Protection: A feature in a UPS that safeguards connected devices

from power surges or spikes, which can occur due to lightning strikes, grid

instability, or other electrical issues.

viii) Transfer Time: The duration it takes for the UPS to switch from using the

main power source to its backup battery when an outage or power failure

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occurs. A fast transfer time is essential to prevent disruption to sensitive

equipment.

ix) Overload Protection: A feature in a UPS that prevents the system from

delivering power beyond its rated capacity. If the connected load exceeds the

UPS’s maximum capacity, it automatically shuts down or activates safety

mechanisms to protect both the UPS and the equipment.

x) AC Power: Alternating Current power, which is the type of electricity commonly

supplied by utility companies. AC is used to power most household and industrial

devices.

xi) DC Power: Direct Current power, which is the type of electricity supplied

by a battery or other similar sources. It is converted to AC by the UPS for use

by most electrical devices.

CHAPTER TWO

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 LITERATURE REVIEW

2.0 Introduction

An inverter is an electrical device that converts direct current (DC) to

alternating current (AC) or signal. The converted AC can be at any required

voltage and frequency with the use of appropriate transformers, switching, and

control circuits. Solid-state inverters have no moving parts and are used in a

wide range of applications, from small switching power supplies in computers,

to large electric utility high-voltage direct current applications that transport

bulk power. Inverters are commonly used to supply AC power from DC sources

such as solar panels or batteries. The inverter performs the opposite function of

a rectifier.

(James Hahn, 2021).

2.1 Types of Inverters

There are three basic types of dc-ac converters: square wave, modified sine

wave, and pure sine wave (see the diagram below). The square wave is the

simplest and cheapest type, but nowadays it is practically not used commercially

because of low power quality. The modified sine wave topologies (which are

actually modified square waves) provide square waves with some dead spots

between positive and negative half-cycles. They are suitable for many electronic

loads, although their THD (total harmonic distortion) is about 25%. The quality

of the inverter output waveform can be expressed by using the Fourier analysis

data to calculate the total harmonic distortion (THD). The total harmonic
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distortion (THD) is the square root of the sum of the squares of the harmonic

voltages divided by the fundamental voltage as shown in equation 2.1.

Priced in the range of $.05-$0.10 per watt, modified Sinewave models are the

most popular low-cost inverters on the consumer market today, particularly

among car and domestic inverters. If you are buying a model whose description

does not state that it is a pure Sinewave type, then most likely it is a modified

one. Note that output voltage waveform in conventional modified Sinewave

DC-AC circuits has only two levels: zero or peak voltage of both polarities. By

adding another voltage level, a designer can reduce THD typically from 25% to

6.5%.

Periodically connecting the output to a specific voltage level with proper timing

can produce a multiple-level waveform which is closer to sinusoidal than

conventional modified Sinewave. A Sinewave inverter produces output with

low total harmonic distortion (normally below 3%). It is the most expensive

type of AC power source, which is used when there is a need for clean

sinusoidal output for some sensitive devices such as medical equipment, laser

printers, stereos, etc. (Barnes, Malcolm, 2023)

There are a number of topologies used in the inverter circuits. Cheap square

wave circuits suitable primarily for hobbyist’s projects may use just a push-pull

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converter with a step-up transformer. Most commercially manufactured models

use a multi-stage concept. With such technique, first a Switching-Mode Power

Supply (SMPS) steps up a voltage from an input source to another DC voltage

corresponding to the peak value of the desired sinusoidal voltage. The output

stage then generates an AC. This stage usually uses a full- bridge or half- bridge

configuration. If a half-bridge is used, the DC-link voltage should be more than

twice the peak of the generated output. Input to output galvanic isolation is

provided by either a high-frequency transformer in the SMPS pre-regulator, or

by a large low-frequency output transformer. If a low-frequency transformer is

used, the sinusoidal voltage is generated on its primary side and transformed to

the secondary side. The output can be controlled either in square-wave mode or

in pulse width-modulated (PWM) mode. Sine wave circuits use PWM mode, in

which the output voltage and frequency are controlled by varying the duty cycle

of the high frequency pulses. Chopped signal then passes through a low pass

Filter to supply a clean sinusoidal output. Although such approach is more

expensive, it is usually employed in the backup devices for home or business

use, which require high quality of AC power. (Rodriguez, August 2022)

2.2 Basic Designs

In one simple inverter circuit, DC power is connected to a transformer through

the center tap of the primary winding. A switch is rapidly switched back and

forth to allow current to flow back to the DC source following two alternate

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paths through one end of the primary winding and then the other. The

alternation of the direction of current in the primary winding of the transformer

produces alternating current (AC) in the secondary circuit.

The electromechanical version of the switching device includes two stationary

contacts and a spring supported moving contact. The spring holds the movable

contact against one of the stationary contacts and an electromagnet pulls the

movable contact to the opposite stationary contact. The current in the

electromagnet is interrupted by the action of the switch so that the switch

continually switches rapidly back and forth. This type of electromechanical

inverter switch, called a vibrator or buzzer, was once used in vacuum tube

automobile radios. A similar mechanism has been used in door bells, buzzers

and tattoo guns. (Owen, 2016)

As they became available with adequate power ratings, transistors and various

other types of semiconductor switches have been incorporated into inverter

circuit designs.

2.3 Advanced Designs

There are many different power circuit topologies and control strategies used in

inverter designs. Different design approaches address various issues that may be

more or less important depending on the way that the inverter is intended to be

used. (Owen, 2021)

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The issue of waveform quality can be addressed in many ways. Capacitors and

inductors can be used to filter the waveform. If the design includes a

transformer, filtering can be applied to the primary or the secondary side of the

transformer or to both sides. Low-pass filters are applied to allow the

fundamental component of the waveform to pass to the output while limiting the

passage of the harmonic components. If the inverter is designed to provide

power at a fixed frequency, a resonant filter can be used. For an adjustable

frequency inverter, the filter must be tuned to a frequency that is above the

maximum fundamental frequency.

2.4 Power Inverters and Waveforms

Inverters, besides coming in a wide variety of power capacities, are

distinguished primarily by the shape of the alternating current wave they

produce. The three major waveforms are square-wave, modified sine-wave and

true sine-wave as shown in Figure 2.1. Almost all inverters rely on push pull

class B amplifier but the wave of the power output largely depends on the type

of oscillator used in the design. For example, if an astable multi-vibrator is used

as the oscillator in an inverter, the wave form at the output would be square

wave because the multivibrator is a square wave oscillator. (Edward Hughes,

2020)

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 Fig 1: Types of inverters’ wave forms
2.5 Square Wave Inverters

Square wave inverters are largely obsolete, as the waveform shape is not well

suited for running most modern appliances. The oscillator as mentioned earlier

determines the output wave form. Therefore, emphases would be laid on the

square wave oscillator. The most common type of square wave inverters is

based on astable multi-vibrator.

2.6 Multi-vibrator

A multi-vibrator is basically an electronic circuit constituting two amplifier

circuits arranged with regenerative feedback used to implement a variety of

simple two-state systems such as oscillators, timers and flip-flops. One of the

amplifiers is conducting while the other is cutoff.

When an input signal to one amplifier is large enough, the transistor can be

driven into cutoff, and its collector voltage will be almost VCC. However, when

the transistor is driven into saturation, its collector voltage will be about 0 volts.

A circuit that is designed to go quickly from cutoff to saturation will produce a

square or rectangular wave at its output. This principle is used in multivibrator.

Multivibrators are classified according to the number of steady (stable) states of

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the circuit. A steady state exists when circuit operation is essentially constant;

that is, one transistor remains in conduction and the other remains cut off until

an external signal is applied. (http://en.wikipedia.org/wiki/Renewable_energy)

The three types of multivibrators are the ASTABLE, MONOSTABLE, and

BISTABLE.

2.6.1 Astable multi-vibrator

The astable circuit has no stable state. With no external signal applied, the

transistors alternately switch from cutoff to saturation at a frequency determined

by the RC time constants of the coupling circuits. It continuously oscillates from

one state to the other. Due to this, it does not require an input (Clock pulse or

other).

2.6.2 Monostable multi-vibrator

The monostable multi-vibrator has in one of the states is stable, but the other is

not. The monostable circuit has one stable state; one transistor conducts while

the other is cut off. A signal must be applied to change this condition. After a

period of time, determined by the internal RC components, the circuit will

return to its original condition where it remains until the next signal arrives.

This circuit is also known as a one shot multivibrator. Bistable multi-vibrator:

The bistable multivibrator has two stable states. It remains in one of the stable

states until a trigger is applied. It then FLIPS to the other stable condition and

remains there until another trigger is applied. The multivibrator then changes

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back (FLOPS) to its first stable state. Such a circuit is important as the

fundamental building block of a register or memory device. This circuit is also

known as a latch or a flip-flop. ( Berndt D, 2022). In its simplest form the multi-

vibrator circuit consists of two cross-coupled transistors. Using resistor-

capacitor networks within the circuit to define the time periods of the unstable

states, the various types may be implemented. Multivibrators find applications

in a variety of systems where square waves or timed intervals are required.

Simple circuits tend to be inaccurate since many factors affect their timing, so

they are rarely used where very high precision is required.

Before the advent of low-cost integrated circuits, chains of multi-vibrator found

use as frequency dividers. A free-running multi-vibrator with a frequency of

onehalf to one-tenth of the reference frequency would accurately lock to the

reference frequency. This technique was used in early electronic organs, to keep

notes of different octaves accurately in tune. Other applications included early

television systems, where the various line and frame frequencies were kept

synchronized by pulses included in the video signal.

2.6.3 Astable Multi-vibrator Circuits

An astable multi-vibrator is also known as a free-running multi-vibrator. It is

called free- running because it alternates between two different output voltage

levels during the time it is on. The output remains at each voltage level for a

definite period of time. If you looked at this output on an oscilloscope, you

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would see continuous square or rectangular waveforms. The astable multi-

vibrator has two outputs, but no inputs as shown in Fig. 2. (Dr. Ulrich, 2021)

Fig. 2. Astable Multi-vibrator

The astable multi-vibrator is said to oscillate. To understand why the astable

multivibrator oscillates, assume that transistor Q1 saturates and transistor Q2

cuts off when the circuit is energized. This situation is shown in Figure 3. We

assume Q1 saturates and Q2 is in cutoff because the circuit is symmetrical; that

is, R1 = R4, R2 = R3, C1 = C2, and Q1 = Q2. It is impossible to tell which

transistor will actually conduct when the circuit is energized. For this reason,

either of the transistors may be assumed to conduct for circuit analysis purposes.

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 Fig. 3: Astable multi-vibrator(Q1saturated) (Gibilisco, 2021)

Essentially, in figure 3, all the current in the circuit flows through Q 1; Q1 offers

almost no resistance to current flow. Notice that capacitor C 1 is charging. Since

Q1 offers almost no resistance in its saturated state, the rate of charge of C 1

depends only on the time constant of R2 and C 1 (recall that T = RC). Notice that

the right-hand side of capacitor C 1 is connected to the base of transistor Q 2,

which is now at cutoff.

Analysis of what is happening is that, the right-hand side of capacitor C 1

becomes increasingly negative. If the base of Q 2 becomes sufficiently negative,

Q2 will conduct. After a certain period of time, the base of Q 2 will become

sufficiently negative to cause Q2 to change states from cutoff to conduction. The

time necessary for Q2 to become saturated is determined by the time constant

R2C1.

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 Fig. 4 : Astable multi-vibrator (Q2 saturated)

The next state is shown in Fig. 4. The negative voltage accumulated on the right

side on capacitor C1 has caused Q2 to conduct. Now the following sequence of

events takes place almost instantaneously. Q 2 starts conducting and quickly

saturates, and the voltage at output 2 changes from approximately -VCC to

approximately 0 volts. This change in voltage is coupled through C 2 to the base

of Q1, forcing Q1 to cutoff. Now Q1 is in cutoff and Q 2 is in saturation. This is

the circuit situation shown in Fig. 4.

Notice that Figure 2.4 is the mirror image of Figure 2.3. In Figure 2.4 Fig. 4 the

left side of capacitor C2 becomes more negative at a rate determined by the time

constant R3 C2. As the left side of C2 becomes more negative, the base of Q1 also

becomes more negative. When the base of Q 1 becomes negative enough to allow

Q1 to conduct, Q1 will again go into saturation. The resulting change in voltage

at output 1 will cause Q2 to return to the cutoff state.

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The output waveform from transistor Q2, is shown in Fig. 5. The waveform of

the output voltage (from either output of the multi-vibrator) alternates from

approximately zero volts to approximately -VCC, remaining in each state for a

definite period of time. The time may range from a microsecond to as much as a

second or two. In some applications, the time period of higher voltage (-VCC)

and the time period of lower voltage (0volts) will be equal. For example, timing

and gating circuits often have different pulse widths as shown in Figure 2.6.

(www.powermaster.com/dashboarding/power-inverters.htm)

Fig. 5 : Square wave output from Q2.

Fig. 6: Rectangular waves

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2.6.3.1 Astable Multivibrator using 555 Timer

An Astable Multivibrator is an oscillator circuit that continuously produces

rectangular wave without the aid of external triggering. So Astable

Multivibrators are known as free running oscillators. Astable Multivibrator

using 555 Timer is very simple, easy to design, very stable and low cost. It can

be used for timing from micro seconds to hours. Due to these reasons, 555 timer

has a large number of applications. (en.wikipedia.org/wiki/power inverter)

Fig. 7: Astable Multivibrator using 555 Timer Circuit Diagram

Fig. 7 shows the circuit diagram of a 555 Timer wired in Astable Mode. 8th pin

and 1st pin of the IC are used to give power, Vcc and GND respectively. The

4th pin is RESET pin which is active low and is connected to Vcc to avoid

accidental resets. 5th pin is the Control Voltage pin which is not used. So, to

avoid high frequency noises it is connected to a capacitor C’ whose other end is

23
connected to ground. Usually C’= 0.01μF. The Trigger (pin 2) and Threshold

(pin 6) inputs are connected to the capacitor which determines the output of the

timer. Discharge pin (pin 7) is connected to the resistor Rb such that the

capacitor can discharge through Rb. Diode D connected in parallel to Rb is only

used when an output of duty cycle less than or equal to 50% is required. For the

sake of explain the working, Circuit Diagram with Internal Block diagram is

shown in Figure 2.8. Since the Control Voltage (pin 5) is not used the

comparator reference voltages will be 2/3Vcc and 1/3Vcc respectively. So, the

output of the 555 will set (goes high) when the capacitor voltage goes below 1/3

Vcc and output will reset (goes low) when the capacitor voltage gets to 2/3 Vcc.

When the circuit is switched ON, the capacitor(C) voltage will be less than

1/3Vcc.

So, the output of the lower comparator will be HIGH and of the higher

comparator will be LOW. This SETs the output of the SR Flip-flop.

Thus, the discharging transistor will be OFF and the capacitorC starts charging

from Vcc through resistor Ra & Rb.

When the capacitor voltage becomes greater than 1/3 Vcc ( less than 2/3 Vcc ),

the output of both comparators will be LOW and the output of SR Flip-flop will

be same as the previous condition. Thus, the capacitor continuous to charge.

Capacitor voltage goes above 2/3 Vcc. (en.wikipedia.org/wiki/power inverter)

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 Fig. 8. Astable Multivibrator using 555 Timer Working

Fig. 8 shows the Astable Multivibrator using 555 Timer Working. When the

capacitor voltage will become slightly greater than 2/3Vcc the output of the

higher comparator will be HIGH and of lower comparator will be LOW. This

resets the SR Flip-flop.

Thus, the discharging transistor turns ON and the capacitor starts discharging

through resistor Rb.

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Soon the capacitor voltage will be less than 2/3 Vcc and output of both

comparators will be LOW. So, the output of the SR Flip-flop will be the

previous state.

So, the discharging of capacitor continuous.

When the capacitor voltage will become less than 1/3Vcc, the output SETs since

the output of lower comparator is HIGH and of higher comparator is LOW and

the capacitor starts charging again.

This process continuous and a rectangular wave will be obtained at the output.

(www.powerelectronics.com)

Capacitor Charges through Ra and Rb.

Thigh = 0.693(Ra + Rb)C 2

Capacitor Discharges through Rb Tlow = 0.693RbC 3

Duty Cycle = Thigh 4

(Thigh +Tlow)

Where Thigh and Tlow are the time period of HIGH and LOW of the output of 555.

From this we can find that Duty Cycle less than or equal to 50% cannot be

obtained. There are two ways to obtain this.

• Inverting the output

• Using a Diode Parallel to resistor Rb

2.7 Inverting the Output

In this method, just compliment the output. Thus,

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 Duty Cycle = T low 5
(Tlow + Thigh).
Where Tlow and Thigh are the time period of LOW and HIGH of output of 555. In

this method, the duty cycle of the output of 555 will be greater than 50% and

that of inverter will be less than 50%.

Duty Cycle of 555 = 1– DutyCycle of inverter. 6

Using a Diode Parallel to resistor Rb,

In this method we will connect a diode parallel to resistor Rb as shown dotted in

the figure 2.7. Thus the charging current of capacitor will bypass the resistor Rb.

Thus Thigh = 0.693RaC (www.powerelectronics.com)

Thus a Duty Cycle less than or equal to 50% can easily obtained.

2.8 Constraints of Square Wave Inverters

Even though the square wave is highly economical due its affordability in terms

of cost of production, it has some clampdown such as:

• High audio noise which turns to be very visible when it is being used to

operate an audio system.

• Incompatibility with certain communication gadgets such as fax machine,

modems, routers and other equipment which run on motors such as fun,

printers, photocopiers etc.

• Low surge power

It is to this fact that new system like the modified sinewave which is built on the

foundations of modified square wave is being introduced.

27
2.9 Pure Sine Wave

Pure or True Sine Wave inverters provide electrical power similar to the utility

power you receive from the outlets in your home or office, which is highly

reliable and does not produce electrical noise interference associated with the

other types of inverters. With its “perfect” sine wave output, the power

produced by the inverter fully assures that your sensitive loads will be correctly

powered, with no interference. Some appliances which are likely to require Pure

Sine Wave include computers, digital clocks, battery chargers, light dimmers,

variable speed motors, and audio/visual equipment. If your application is an

important video presentation at work, opera on your expensive sound system,

surveillance video, a telecommunications application, any calibrated measuring

equipment, or any other sensitive load, you must use a Pure Sine Wave inverter.

(diffenderfes, 2020)

2.10 Modified Square/SineWave Inverter

An inverter allows the use of 230V electrical appliances from a battery or a

solar battery. It must therefore supply a voltage that corresponds to an RMS of

230 Volts sine-wave like household main supply or similar. Sine-wave voltages

are not easy to generate. The advantage of sine-wave voltages is the soft

temporal rise of voltage and the absence of Harmonic oscillations, which cause

unwanted counter forces on engines, interferences on radio equipment and surge

currents on condensers. On the other hand, square wave voltages can be

28
generated very simply by switches, e.g. electronic valves like MOSFET

transistors. In former times electromagnetically switches, which operated like a

door bell were used for this task. They were called “chopper cartridge” and

mastered frequencies up to 200 cycles per second. The efficiency of a modified

square wave inverter is higher than the appropriate sine wave inverter, due to its

simplicity. With the help of a transformer the generated modified square wave

voltage can be transformed to a value of 230 Volts or even higher (radio

transmitters). (Martindale, 2022)

Fig. 9: Sine-wave voltage and conventional square wave voltage with both

230 Volt R.M.S

Fig. 9 above shows a sine-wave as well as a square wave voltage with in each

case an rms of 230 Volts. In both cases an electric lamp would light with the

same intensity. This is, as we know, the definition of rms. As we recognize in

Fig.7. However, the peak value of the sine-wave voltage is 325 Volts, i.e. factor

√2 more than rms. For electric lamps this is insignificant and electric engines

are appropriate for it. Electronic devices were even designed for the peak

voltage of sine-wave voltage, because internally they generate DC voltage from

29
the AC supply voltage. A condenser will be loaded on exactly the peak value of

the sinewave voltage. Electronic devices thereby usually cannot be operated on

230Volts square waves. The industry nevertheless manufactured modified

square wave inverters according to this principle in former times.

The inverter works with a trick, to obtain the same results from square wave

voltage as for modified sine-wave voltage.

Fig .10 : Voltage with duty cycle 25% for 230 Volts r.m.s (“Modified sine”)

Square wave voltage in Fig. 10 develops the same peak value as sine-wave

voltage of 230Volts, i.e. 230 Volt * √2 = 325 Volts and nevertheless thereby

obtains the demanded r.m.s. of 230 V. Square wave voltage as shown in the

previous Figure (full half wave) with peak value of the corresponding sine-wave

voltage would cause double amount of electrical power on electric consumers.

The trick is, to switch the output power only for one half of every conducting

cycle, thus resulting on a duty cycle of 25% on behalf of the complete

oscillation period. If the calculated double amount of electric power will be

generated only half the time effective power remains the same. Industry called

this cam shape “modified sine”, in order to be able to differentiate the devices

from conventional square wave inverters. (Martindale, 2022)

30
The inverter may feed nearly all electrical appliances, designed for 230 Volts,

with exception of rotary field engines that use condensers for generation of an

auxiliary phase (condenser engines). Engines of this type are used in most

refrigerators, washing machines, dishwashers and some few machine tools.

Fluorescent lamps with a series inductivity to limit the operating current won’t

work correctly on our inverter not necessary problem with the output waveform

but in terms of power rating and specific function the inverter is designed for.

This problem can be solved by increasing the duty cycle on more than 25%

while decreasing the peak voltage to 275 Volts. Instead, fluorescent lamps with

electronics (energy saving lamps) will work very well on the inverter. There

may also be problems with some small plug power supplies. An increased

magnetizing current results on square wave voltages, while there would be a

predominantly inductive load

(cosj<< 1). Dutycycle 25% and cosj =0 will result in load currents up to factor p

/2 (approx. factor 1.5).

This project is suitable for:

• Electric drills, fretsaws, circular saws, electric chain saws, grinders

• Vacuum cleaners, coffee machines, irons, dryers, mixers, sewing

machines, electric razors, etc.

• lamps, energy-savings lamps

• Electronic devices, e.g. music amplifiers, battery chargers

• Computers and accessories

31
 • Televisions and radios

• Radio transmitters, high voltage generators, among other things.

2.10.1 Modifying Sine Wave Using Discrete Square Waves

Fig. 11: Modified sine wave

Fig. 11 provide an interesting design of a single modified sine wave cycle made

by chopping a few square waves. Here, each positive and negative half cycle

contain 3 discrete individual narrow square waves, each block is separated by a

notch, the center two―pillars‖ are identical but are twice in magnitude than the

extreme ones.

The average value of this special arrangement of discrete square waves

effectively imitates a sinusoidal wave. This configuration is as good as a pure

sine AC waveform and thus will be suitable to operate almost all appliances

safely. In fact, the present design is much more efficient than the usual circuits

used in many inverters. From this circuit it’s possible to get an efficiency of

almost 90%, because here the output devices are either turned fully on or fully

off.

32
2.11 Transistor

A bipolar transistor is a three terminal (base emitter and collector) circuit

amplifying device in which a small input current can control the magnitude of a

much longer output current. The term “bipolar” means that the device is made

from mi conductor materials in (majority and minority) charge carriers.

The transistor is made from a three layer sandwich of N-type and P- type

semiconductor materials with the base terminal connected to the control layer

and the collector and emitter terminals connected to the outer layers. If it uses

NPN condition sandwich as in Fig. 12 (a), it is known as an NPN transistor and

uses the standard symbol of Fig. 12 (b): if it uses a P-N-P structure as in Fig. 13

(a) it is known as a PNP transistor and uses the symbol of Fig. 13 (b).

Fig. 12: Basic Construction and symbol of NPN transistor

33
 Fig. 13: Basic Structure A, symbol, B, of PNP transistor

2.12 Transformer

Alternating current and voltage can be increased or reduced with ease. This is

one tremendous advantage it has over direct current the equipment used for the

purpose of varying ac voltage is called a transformer. It is basically a device that

transfers energy from one circuit to another by electromagnetic induction. This

transfer is usually, but always accompanied by a change of voltage.

2.12.1 Principle of Transformer

Fig. 14: A Transformer Schematic

34
Fig. 14 shows the general arrangement of a transformer. An iron core, C

constitute of lamented sheet about 0.35mm thick insulated from one another by

thin layers of paper or by spraying the lamination with a mixture of flows chalk

and water which when dried adheres to the metals. The purpose of laminating

the core is to reduce losses by the core. The core (laminated iron core) is

referred to as the limbs and the top and bottom portion are the yokes. Coils P

and S are wound on the Limbs. Coil P is connected to the supply and is termed

the primary coils and coil S is connected to the load and is termed the

secondary. An alternating voltage applied to P circulates on alternating current

through p and this current produces an alternating flux in the iron core, the mean

path of this flux being represented by the dotted line D. If the whole of the flux

produce by P passes through S, the e.m.f. induced in each turn is the same for P

and S. Hence, if N1 and N2 be the number of turns on p and s respectively.

Total emf induced is S = N2 x emf per turn = N2 7

Total emf induced in P N1 x emf per turn N1

When the secondary is on open- circuit its terminal voltage is the same as the

induced e.m.f. The primary current is then very mall so that the applied voltage

Ns is practically equal and opposite to the emf induce in p, hence,

V2 N2
8 =

V1 N1

35
Equation 8 is the turn ratio of primary and secondary of the transformer. Since

the full load efficiency of a transformer is nearly100 percent. I, V, x primary

power factor = I2V2 × secondary power factor 9

Note: Power factor is defined as the ratio of true power (or watts) to apparent

power (or volt-amps). They are identical only when the current and voltage are

in phase then power factor will be 1.0.

But the primary and secondary power factors at full load are nearly equal:

I1 = V1 10
I2 V2

Equation 10 shows the relationship between the primary and secondary current

of the transformer.

An alternative eliminating method of deriving the relationship between the

primary and secondary current is based upon a comparison of the primary and

secondary ampere-turns, when the primary ampere-turns are just sufficient to

produce the flux necessary to induce an e.m.f. That is practically equal and

opposite to the applied voltage. This magnetizing current is usually about 3-5

percent of the full-load primary current. Also, the flux and the e.m.f. induced in

the primary are reduced slightly. But this small change may increase the

difference between the applied voltage and e.m.f. induced in the primary from

0.05 percent to, say, 1% in which cases the new primary current would be 20

times the no-load current. The demagnetizing ampere-turns of the secondary are

thus nearly neutralized by the increase in the primary ampere-turns and since the
36
primary ampere-turns on no-load are very small compared with the full load

ampere turns:

Full-load primary ampere-turns = full-load secondary ampere turns

i.e. I1N1 = I2N2 11

So that,

I1 = N2 = V2 12

I2 N1 V1

Equation 12 shows the relationship between the primary and secondary ampere

–turns ratio of the transformer.

It will be seen that the magnetic flux forms the connection between the primary

and secondary circuit and that any variation of the secondary current is

accompanied by a small variation of the flux and therefore of the e.m.f induced

in the primary, thereby enabling the primary current to vary approximately

proportionally to the secondary current.

This balance of primary and secondary ampere-turns is an important

relationship where ever transformer action occurs (Lasance, 2020).

2.13 Power Supply

All electronic and electrical appliances require some kind of direct or converted

power to function. Most devices also require that such power be maintained in a

specified range by a process known as power regulation. The equipment or

37
circuit used to achieve this purpose is called a power circuit (or power supply).

(Edward

Huglies Electrical Technology. Fourth Edition)

2.14 Battery

A battery is an energy storage device that can deliver energy to electronic circuit

using direct current (D.C.). There are many different battery technologies

available today. However, one of the oldest, is the Lead-acid battery, which is

the most suitable to stationary solar power applications. There are two main

reasons for this, a large amount of energy storage costs very little compared to

other technologies and it operates over a narrow voltage range which makes it

ideal for powering common appliances. This type of battery does have its

disadvantages, notably the fact that it is easily damaged by excessive discharge.

Each cell of a lead acid battery has a nominal voltage of 2 volts; hence a 12

volts battery is constructed of 6 cells in series. A standard car battery is an

example of a 12-volt monobloc. (29)

2.14.1 Primary Battery

This is an energy storage device that can deliver energy but cannot be
recharged.

2.14.2 Secondary Cell or Gel Batter

This is a type of battery that uses a galled electrolyte solution. These batteries

are sealed and are virtually maintenance-free. Not all sealed batteries are the gel

cell type.

38
2.14.3 Deep-cycle batteries

The term deep-cycle battery simply refers to batteries that are designed for

regular discharging by 50% or more. The term is applied to many different

forms of battery from small 6- or 12-volt batteries to much larger batteries

consisting of separate two cells. Most traction batteries, that is those designed to

propel electric vehicles such as fork-lift trucks, can be considered to be deep-

cycle.

2.14.4 Leisure Batteries

The term ‘leisure battery’ refers to a battery which is a compromise between the

low cost of a car battery and the long life of a true deep-cycle battery. They

have much longer life that the car battery when regularly discharged and are

much less expensive than a true deep-cycle battery. Their use is common in

applications such as caravans, where the usage pattern is not as intensive.

2.14.5 Battery Operation

(a) Charging: The voltage at which a lead-acid battery is charged must be

strictly regulated. If the charging voltage is too high, then excessive gassing

will occur, leading to a loss of electrolyte and possible plate damage. On the

other hand, tool low a battery will lead to the plates becoming sulphated

which cause a loss of capacity.

(b) Discharge: Battery must be protected from damage by over-charging. As

the battery discharges, the voltage at the terminal decreases.

39
(c) Battery Ratings: Batteries come in different sizes and designs and their

storage capacity is determined by their volume. Batteries are mostly rated as

ampere/hour, that is the current it can deliver continuously for one hour

before it is completely discharged. the battery sizes range from 12volt/7Ah

the small ones found in UPS to 12V/200Ah used in the industrial backup power

supplies, 12volts/18Ah, 12volt/60Ah, 12volts/100Ah, etc.

2.14.6 Ampere-Hour (Amp-Hr, All)

A unit of measurement for battery electrical storage capacity, obtained by

multiplying the current in amperes by the time of discharge in hours (examples

a battery delivers 5 amperes for 20 hours has 100 amp-Hr rating).

2.14.7 AH Capacity

The ability of a fully charge battery deliver a specified quantity of electricity

(AmHr, AH) at a given rate (Amp, A) over a definite period of time (Hr). The

capacity of a battery depends on a number of factors, efficiency and

compatibility of the charge discharge circuit active materials, adhesion to grid,

number design and dimension of plate spacing design of separators, specific

gravity and quantity of available electrolyte grid alloys final limiting (voltages

discharge/charge) rate, temperature, internal and external resistance age and life

of the battery (bank).

40
 CHAPTER THREE

MATERIAL AND METHOD

3.1 MATERIAL

List of Components

R1 = 1.5kΩ, 0.25watts (Resistor)

R2 = 143kΩ, 0.25watts (Resistor)

R3 = 143kΩ, 0.25watts (Resistor)

Q1 = C1815 (Transistor)

Q2 = C1815 (Transistor)
C₁ = 0.1μF, 50Hz (Capacitor)

C2 = 0.1μF, 50Hz (Capacitor)

MJ1503 (Transistor)
Q3 =

Q4 = MJ1503 (Transistor)

T1 = Transformer 3/240Volts

3.2: Method

For smooth implimentation of this project the system was divided into four main

sectors as shown in the block diagram of fig. 15

The essential architecture of a basic inverter is as shown in the block diagram of

fig. 15.

41
 Fig. 15: Inverter Block Diagram

3.2.1 Design of the Oscillator Circuit

In this section, an astable multivibrator, transistor version was used as a uniform

wave generator. Fig. 16 shows the diagram of Transistor in Astable mode.

Fig. 16: Transistor Astable

42
The input and output waveforms to fig. 16 circuit are as shown in fig. 17(a) and

(b). Note again that this circuit as an oscillator is self-triggered, as soon as

power is restored to the circuit, oscillation commences automatically.

Fig. 17: (a and b) Dc Power Input Signal

(a) Output from transistor Q1

(b) Output from transistor Q2

43
Note that from Fig. 17 that the output from the two transistors is

complementing, in other words opposite to each other.

T = 1.4 RC 13

and since,

F= 1 14

F = 1 15

1.4RC

The oscillator must run at 50 cycles per second. That is 50HZ.

Let C = C1= C2= 0.1μF 16

and R₁= R4 = 1.5Ohms 17

Also,

F =50Hz

So, we need to find the value of R=R2=R3 needed for 50Hz operation.

If the circuits to generate the required uniform square waveform are necessary
for inverter operations, the following conditions need to be met.
R₁ = R4

R2 = R3 18
C1 = C2

Q₁ = Q₂

44
Usually, period of oscillation for a uniform transistor astable multivibrator is

determined by or proportional majorly to the resistance and capacitance time

delay component as expressed in equation 13.

So, we need to find the value of R=R2=R3 needed for 50Hz operation. From the

equation 3.3, we have

F= 1

1.4RC

R= 1

1.4FC 19

R = 1 = 142857.134 = 142.8k or
143k(approximately)

1.4 x 50 x 0.1 x 10-6

Q1 was chosen as C1815, a general-purpose transistor. The resulted circuit with

values is shown in fig. 18

45
 Fig.18 final output of the oscillator circuit

The circuit of Fig. 18 is the final output of the oscillator circuit which will then

drive the switching circuit.

3..2.3 Design of the Electronic Switch

The electronic switch is none other but a transistor biased in its switching or

saturation mode. Transistors are specially packaged to handle currents as small

as several Ampere, up to tens of amps.

For this design, after a careful browsing of the data books, the transistor that

best suit our purpose is:

Transistor identify - MJ15003

Junction arrangement - NPN

Application - audio output, switching and high-power stages.

46
Maximum supply voltage, VCE - 140 Volts

Maximum fed collector current lc - 20 Amps

Maximum power dissipation Pcmax - 200Watts

Maximum operating frequency 2mHz

The transistors are two in number, a kind of complementary or push pull

configuration.

One transistor switches the positive cycle while the other switches the negative

as shown in fig. 19

47
 Fig. 19: Power Switching Stage

The result of this kind of switching configuration is an alternating square wave

which can be fed to a transformer as we shall see in the next stage.

48
3.2.4 Design of Output Stage

Certain parameters in the inverter, will determine the selection of the

transformer for this stage.

(a) The transformer must have the following configurations shown is fig. 20.

Fig. 20 Transformer architecture

Effective turn’s ratio for the full coil is

Effective turn’s ratio for the half coil is expressed as,

49
(b) Power calculations

To drive a load of 1000watts at 240 volts, we shall estimate the current rating

(which also determines its physical size) of the transformers as follows:

Power (P) = current (1) ×voltage (v), P = 1 × V 20

21

In this case:

I= 4.17Amps

To drive a 500 watts load,

50
I = 2.1 Amps

However, in the 1000 watts range, the standard rating available was 4amps, so

the power that we could get from this rating will be.

P = 1 × v = 4×240 = 960

P =960 watts

The next commercial specification was 5amps which will be much too high.

3.2.3 Heating and Cooling

Inverter operation involves a lot of heat generation. The heat producing

components are power transistors and transformer. For prolonged operation, an

internal cooling fan will be required and in addition, the transistors will be

placed on a heat sink using the appropriate insulator to isolate both of them

electrically.

3.2.4 Battery

The inverter is not complete without a battery. The best battery to be used in an

inverter is a deep cycle type which has a long span of depth of discharge. Much

as we are not expressed to design the battery there are the specifications for the

battery selected for this project.

Voltage (v): 3.7 to12

Capacity (AH): 7

Electrolyte: Lead acid

51
The complete circuit diagram of the inverter is shown in fig. 21

52
 Fig. 21 Inverter circuit

Basic Working Principle of an Inverter

Once the circuit is switched on, the 12V DC battery supplies voltage to the

switching characteristics of the semiconductor devices (transistors), to control

the power supply voltage and current through rapid switching, thereby

53
converting the DC power into alternating current of corresponding frequency

and voltage.

Specifically, when the input DC power passes through the transistor in the

inverter, it is divided into a series of pulse signals, which are filtered and

adjusted to produce AC power with the same frequency, amplitude and

waveform as the desired output.

Finally, the AC power produced by the transistors is further stepped up to an

output of 240V by the step-up transformer which can act as the input to load

such as lighting bulb, charging of phone, etc.

3.2.5 System Development

The construction of this system requires several tools and equipment other than

the specific electrical and electronics components required for this system.

Some of this tool involves testing and measuring, soldering and joining,

tightening and loosing.

3.3 Hand Tools

3.3.1 Soldering iron

For electronics work the best type is one powered by mains electricity it should

have a heatproof cable for safety. The iron’s power rating should be 15 to 25W

and it should be fitted with a small bit of 2 to 3mm diameter for heat sensitive

components like ICs and small transistors and 60 to 100watts for thick cables

and joints. The soldering iron is shown in fig. 22

54
 Fig. 22 Soldering iron

Low voltage soldering irons are available, but their extra safety is undermined if

one have a mains lead to their power supply. Temperature controlled irons are

excellent for frequent use, but not worth the extra expense if one are a beginner.

Gas-powered irons are designed for use where no mains supply is available and

are not suitable for everyday use. Pistol shaped solder guns are far too powerful

and cumbersome for normal electronics use. (Pipemaster Soldering Tool”

Retrieved 2022-07-20).

3.3.2 Soldering iron stand

One must have a safe place to put the iron when one not using it. The stand

should Include a sponge which can be dampened for cleaning the tip off the

iron. Fig. 23 shows the picture of a soldering iron stand. (Pipemaster Soldering

Tool”

Retrieved 2022-07-20)

55
 Fig. 23 Soldering iron stand

3.3.3 De-soldering pump (solder sucker)

A tool for removing solder when de-soldering a joint to correct a mistake or

replace a component. This is shown in fig. 24 ( Pipemaster Soldering Tool”

Retrieved 2022-07-20)

Fig. 24 De-soldering pump (solder sucker)

3.3.4 Reel of solder

The best size for electronics is 22swg (SWG =standard wire gauge). The fig. 25

shows the pictures of reel of solder.

Fig. 25 Reel of solder

56
3.3.5 Side Cutter

For trimming component leads close to the circuit board. (Scott P. Schneider

(2021)

Fig. 26: Side cutter

Figure 3.12 above shows the picture of side cutter.

3.3.6 Wires tripper

Most designs include a cutter as well, but they are not suitable for trimming

component leads. Fig. 27 below shows the picture of wire stripper. (Scott P.

Schneider (2019)

Fig. 27 Wire Stripper

3.3.7 Small pliers

Usually called ‘snipe nose’ pliers, these are for bending component leads etc. If

one put a strong rubber band across the handles the pliers make a convenient

57
holder for parts such as switches while one solder the contacts. Fig. 28 shows

the picture of small plier (Scott P. Schneider (2019)

Fig. 28: Small plier

3.3.8 Small flat-blade screwdriver

For scraping away excess flux and dirt between tracks, as well as driving

screws. Shown below in fig. 29 is the picture of small flat-blade screwdriver

Fig.29: Small flat-blade screw driver

3.3.9 Heatsink

One can buy a special tool, but a standard crocodile clip works just as well and

is cheaper. Fig. 30 below shows the picture of heatsink (Eggink, H.J., 2021)

Fig.30 Heatsink

58
3.3.10 PCB rubber

This is an abrasive rubber for cleaning PCBs. It can also be used to clean strip

board where the copper tracks have become dull and tarnished. Fig. 31 shows

the figure of PCB rubber. (Lasance, 2019)

Fig. 31. PCB rubber

3.3.11 Small electric drill

Ideally this should be mounted in a drill stand. One will need a range of small

drill bits, but for most holes a 1mm bit is suitable. Larger holes can be drilled

with a hand drill but 1mm bits are too fragile to use reliably in a hand drill. Fig.

32 shows the picture of a small electric drill

Fig. 32. Small battery powered electric drill

59
3.4 Testing and Measuring Tools

These instruments are used to measure frequency, waveform, voltage, current

and resistance.

3.4.1 Oscilloscope

An oscilloscope’s primary function is to provide a graph of a signal’s voltage

over time. This is useful for measuring such things as clock frequencies, duty

cycles of pulse-width- modulated signals, propagation delay, or signal rise and

fall times. It can also alert one to the presence of glitches in one logic or

bouncing switches. (Kularatna, Nihal, 2023)

The oscilloscope (also known as a scope, CRO, DSO or, an O-scope) is a type

of electronic test instrument that allows observation of constantly varying signal

voltages, usually as a two-dimensional graph of one or more electrical potential

differences using the vertical or ‘Y’ axis, plotted as a function of time,

(horizontal or ‘x’ axis). Although an oscilloscope displays voltage on its vertical

axis, any other quantity that can be converted to a voltage can be displayed as

well. In most instances, oscilloscopes show events that repeat with either no

change, or change slowly.

Oscilloscopes are commonly used to observe the exact wave shape of an

electrical signal. In addition to the amplitude of the signal, an oscilloscope can

show distortion, the time between two events (such as pulse width, period, or

rise time) and relative timing of two related signals.

60
One of the most frequent uses of scopes is troubleshooting malfunctioning

electronic equipment. One of the advantages of a scope is that it can graphically

show signals: where a voltmeter may show a totally unexpected voltage, a scope

may reveal that the circuit is oscillating. In other cases, the precise shape or

timing of a pulse is important.

In a piece of electronic equipment, for example, the connections between stages

(e.g. electronic mixers, electronic oscillators, amplifiers) may be ‘probed’ for

the expected signal, using the scope as a simple signal tracer. If the expected

signal is absent or incorrect, some preceding stage of the electronics is not

operating correctly. Since most failures occur because of a single faulty

component, each measurement can prove that half of the stages of a complex

piece of equipment either work, or probably did not cause the fault. Fig. 33

shows the picture of an Oscilloscope. (Kularatna, Nihal, 2023)

Fig. 33. Oscilloscope

61
3.4.1.1 The Basic Oscilloscope Controls

i) Vertical - Controls the vertical alignment of the traces as well as which traces

are shown, their scale, which one is the selected one, etc. Note that only the

currently selected trace will be affected by the controls in this group.

ii) Horizontal - Controls the time scale and position. Note that all traces are

affected simultaneously by these controls.

iii) Trigger - Controls the triggering. This is useful for horizontally aligning a

repeating signal with itself.

iv) Acquire - Controls the method of acquiring samples. It also has the auto set

button that will cause the oscilloscope to automatically choose settings for all

the other controls that it thinks will best display the current waveforms.

v) Miscellaneous - This section is the unlabeled set of controls that is at the top

of the control panel. The controls in this section are mostly high-level functions

that are not specific to a given waveform. It is in this section that one finds the

“General Purpose Knob” referred to later.

Selector buttons along the right and bottom of the screen (not shown in picture)

– These are used to select from menus that appear on the bottom and right of the

screen, just like one would do with an ATM machine at the bank.

62
3.4.2 AVOmeter

The AVO meter was a British brand of multimeter, latterly owned by Megger.

The most widespread of the range was the Model 8, which was produced in

various versions from the 1950s until 2008, the last version being the Mark 7.

It is often called simply an AVO and derives its name from the first letter of the

word’s amperes, volts, and ohms. It was conceived by the Post Office engineer

Donald Macadie in 1923.

3.4.2.1 Technical Features

It was by far the best instrument of its kind in the UK from 1923 to at least

the1960s. Almost uniquely for a radio repairman’s multimeter it measures

alternating current up to 10 A as well as AC and DC voltages up to at least 1000

V. The Model 8 Mk. V included additional inputs to measure up to3000V. As

an ohmmeter it measures from 0.1 Ω upto 200 kΩ in three ranges. The

instrument has an accuracy of ±1% of FSD on DC ranges and

±2% on AC ranges. Its maximum current draw of 50 μA at full-scale deflection

(corresponding to 20,000 ohms per volt) is sufficient in most cases to reduce

voltage measurement error due to circuit loading by the meter to an acceptable

level. A pair of rotary switches are used to select the range to be measured,

being arranged in such a way as to minimize the risk of damage to the

instrument should

63
the wrong range be selected. Further protection is provided by an overload

cutout and fuses. Fig. 34: shows the picture of an AVO metre.

Fig. 34: AVO meter

64
 CHAPTER FOUR

RESULTS

4.1 Result

The Simulated Circuits at various stages are shown in Fig 34 to 36 using a Simulink
(MATLAB) software.

The typical wave pattern of a modified sine wave inverter is shown in fig 34 below.

Fig. 34: Simulated wave pattern of a modified sine wave inverter

Fig. 35: Simulated waveform at the output of the transformer

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Finally, the fig: 36 below is the simulated Waveform after proper filtration using

capacitors at the output of the transformer.

Fig. 36: The simulated Waveform after proper filtration using capacitors at the

output of the transformer.

To confirm that the output of the uninterrupted power supply is a desired one,

the simulation of the circuit was carried out using Simulink software.

Observations from the simulated output signals were taken into cognizance,

hence the simulation was a success and the systems produces the required

waveform.

Hence, the fact remains undisputed that it is possible to generate electricity even

though for a limited period, but without noise and instantly consumable fuel

using the power inverter.

4.2 Cost Benefits Analysis

The cost of the system would have been lower if the components were

purchased on a high quantity.

66
The system was designed based on the electronics components available in the

country.

4.2.1 Material List

Table 4.1 Material List
ITEM UNIT TOTAL
PARTS DESCRIPTION QUANTITY
NO COST (#) AMOUNT (#)
1 Bulb 1 600 600

2 50V/0.1uf 2 200 400

3 1.5kΩ 2 500 1000

4 143 kΩ 2 600 1200

5 MJ15003 2 1000 2000

6 100AFuse 1 200 400

7 Veroboard 1 1000 1000

8 Power Cable 1 1000 1000

220V/9-0-9 Centre-Tapped
9 1 5000 5000
Transformer
10 13Amps mains socket 1 500 500

11 Casing 1 1000 1000

12 10mmAuto flex cable 1 1000 1000

13 Battery 1 6000 6000

14 Heat sink 2 400 800

transportation 5000 500

Sub Total 26,100

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 CHAPTER FIVE

DISCUSSION OF RESULT, SUMMARY, CONCLUSION AND

RECOMMENDATION

5.1 Discussion of the Result

5.1.1 Modified Sine Wave Electricity Effect on Loads

Different appliances were affected to greater and lesser degrees by the different

forms of AC.

Resistive loads such as incandescent light bulbs and heat producing appliances

such as kettles, jugs, irons, radiators and stoves overloaded the system during

testing. Universal motors with brushes and commutators which are found in

most hand tools and many kitchen appliances such as food processors, blenders

and centrifugal type juice extractors operated well with the modified sine wave

inverter.

Inductive loads ran with a little noise and got warmer. Inductive loads with

voltage transformers and motors like those often found in refrigerators, freezers

and washing machines. Induction motors also need a comparatively high surge

current to start up and as such could not run with the system due to the capacity.

For a ‘modified sine wave inverter to handle an inductive load well, it needs to

have a good surge capacity, but it also needs to have a feature referred to as

‘deadspace clamp’. Some appliances run better with modified sinewave which

noticeably would operate less well on square and stepped wave AC inverters.

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Those affected include:

• Some of the latest sewing machines

• Some programmable timers

• Microwave ovens (which operate more slowly)

• Some battery chargers

• Some cordless appliances

• Some dimmer switches

• Some digital clocks

• Some variable speed devices such as fans

• Some hi-fi and other sound equipment

• Some TVs and video equipment • Some Fax’s and Laser Printers

• Iron ballasted fluorescent lights.

This inverter is accompanied by the following features making it very

significant;

• The system uses micro components that do not only reduce the weight or

size of the circuit but also reduce the cost of operation as DC battery of as

low as 3.7V can be used to power the circuit.

• Low cost modified sine wave inverter to upgrade on the square wave inverter

without increasing cost of production.

• Microsecond automatic load transfer and switching to avoid computer based

systems from restarting.

Low battery power consumption.

69
70
5.2: Summary

A modified sine wave UPS design involves converting DC power from a battery into

an AC output that resembles a sine wave but with a stepped or "modified"

waveform. This design prioritizes cost and simplicity over the perfectly smooth

output of a pure sine wave UPS.

5.3 Recommendations

This circuit will need to be modified to perform the function such as enable low
shutdown to avoid damage to cells thereby prolonging battery life.

Also, Adequate time should be allotted for research.

This project is highly recommended for schools, churches industries and in

situation where there is need for alternative power backup.

5.4 Conclusion

At the end of the experiment the inverter proved to be a huge success. The

success of this whole is evident from the success of its component parts. First

the battery was able to withstand the current because its cells were still very

active and its electrolyte intact and of the optimum specific gravity value.

Secondly, the Oscillator was able to generate the right frequency. The

measurement of the frequency at the oscillator output gives a value of 50Hz.

Using this frequency from the oscillator, the power transistor was able to pulse

the battery power at the rate of 50 times per second, when this pulsating power

signal was fed to the transformer using a multimeter give a value 240V.

71
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