BATAAN PENINSULA STATE UNIVERSITY

COLLEGE OF ENGINEERING AND ARCHITECTURE

DEPARTMENT OF ELECTRONICS ENGINEERING

City of Balanga, Bataan

A Project Study on

SOLAR-POWERED AC/DC POWER SUPPLY FOR

ELECTRONICS ENGINEERING LABORATORY

In partial fulfillment of the requirements for the degree of Bachelor of Science in

Electronics and Communications Engineering for the subject ECPF – 521

(Project/Feasibility Study)

By:

Caraan, Irish Jane D.

De Leon, Teddy M.

De Jesus, Kimberly Rose P.

Llamzon, Syrah Dee O.

Parreño, Christian Joseph M.

April 2015

ABSTRACT

This project study aims to design and construct a solar independent AC

and DC power supply for powering low voltage experiment boards and

breadboard circuits in laboratory exercises of electronics engineering students.

By utilizing solar energy as a source, energy consumption from the electrical

power grid is lessened. It also provides students with a way to conduct their

experiments even in cases of power outage. The power supply will also have a

USB port similar to a universal charger that can charge smartphones and tablets

which are often used by students to search for datasheets, proper usage, and

calibrations of the different components and equipment used during experiments.

The prototype is design with consideration to voltage range, duration of use and

power requirement. The performance of the power supply will be assessed in

terms of time of operation, voltage stability, voltage regulation and efficiency.

A C K N O W L E D G E M E N T S

The proponents would like to extend their gratitude and appreciation to the

following persons who have shown their support and have been an integral part

in the progress and completion of this design.

To Engr. Rodrigo C. Muñoz, Jr., their project adviser, for his patience and

assistance in the preparation and completion of this study,

To their instructors and mentors, especially Engr. Jane Salenga and Engr.

Greg Mallari, for sharing their professional and educational knowledge that

served as the foundation of this project,

To their classmates, for supporting them despite undergoing the same

hardships in their own project studies,

To their families and friends, for inspiring them to work hard in this project

and for understanding and attending to their needs,

And above all, to the Lord God, who bestowed them with intelligence and

provided them with the determination to put this project together up to the end.

Chapter 1

INTRODUCTION

Background of the Study

Laboratory experiments play a crucial role in developing the skills and

knowledge of electronics engineering students. It serves as their stepping stone

in knowing the fundamentals of the ECE principles. It also familiarizes them to

the different components and equipment that they might encounter in their future

trainings or work. Furthermore, by performing these experiments and proving that

the principles are true and valid, students will become more appreciative of their

chosen course.

To provide a good learning experience, a laboratory must be well-

equipped with apparatus needed in the experiments. Since most laboratory

exercises for electronics engineering need to input different values of currents

and voltages to the circuit to be tested, a power supply is also required. However,

the power supply is useless in times of power outage because it is dependent on

the ac mains power source. This will interrupt or halt the ongoing experiments

and time will be wasted in waiting for the power to return. The inability of the

students to perform or finish the scheduled experiments due to power outage can

also fade the enthusiasm of the students in doing hands-on practicum.

As an alternative to the ac mains power source, a solar power supply can

be used. It can be used not only during power outage but also as a way to lessen

off the grid power consumption. Running the electric grid in the presence of

increasing fuel costs and growing environmental concerns will require new

technologies and ways to use them. Utilizing electricity from renewable energy

sources such as solar energy can reduce fossil fuel consumption and minimize

the environmental impact of electricity use.

Statement of the Problem

This project study aims to design and construct an AC and DC power

supply for electronics engineering laboratory by using solar energy instead of

using electricity from the AC mains outlet as with power supplies typically used in

school laboratories. Specifically, this study seeks to answer the following

questions?

1. How can solar energy be used as a power source for the power supply?

2. How long should the solar panel be exposed to sunlight before desired

results is acquired?

3. How can circuits for ac and dc voltage source be combined in the power

supply?

4. How can the prototype be designed to achieve high reliability and high

efficiency?

5. What are the materials to be used in constructing the prototype?

Significance of the Study

Power supply plays a vital role during laboratory activities of students in

the field of electronics. The students will benefit by using the solar powered AC

and DC power supply to continue their experiments even in times of power

outage.

This study may also spark the interest of succeeding graduating

electronics engineering students to utilize renewable energy in their projects.

Objectives

General Objective

To design and construct a prototype AC and DC power supply using solar

energy for the use of electronics engineering student in their laboratory

experiments.

Specific Objectives

1. To construct a solar powered power supply that can output an adjustable

DC output from 0 to 40 V DC, an adjustable AC output from 0 to 40 V AC

and charger output of 5V DC to charge portable devices like tablets,

smartphones and cellular phones.

2. To make a power supply that will last ten (10) hours using DC output, six

(6) hours using AC output and one and a half (1½) hours using the

charger for portable devices.

3. To assess the performance of the prototype power supply by computing

its efficiency and by testing its voltage regulation and output stability.

Scope and Delimitation

This study is limited on the use of AC and DC power supply for laboratory

experiments. The power supply is designed to be used on laboratory

experiments performed by Electronics Engineering students and may not reach

the requirements for experiments by Electrical, Mechanical and other engineering

students.

Since the power supply is battery based, it should be recharged when

there is sunlight for it to be useable in times of power outage. This study will

spend two months to be finished.

Chapter 2

Review of Related Literature

This chapter includes discussion on relevant facts about solar energy and

its application in electricity generation.

Presently, the world is highly dependent on petroleum, coal and natural

gas for its energy consumption. These fossil fuels amount to 78.4% of the total

world energy consumption compared to 2.6% for nuclear energy and 19% for

renewable energy (REN21 Renewables 2014 Global Status Report, 2014).

These fossil fuels are expended not only to run our vehicles and supply us with

all types of consumer goods thru manufacturing but also to provide us with

electricity.

Fossil fuels are exhausted to supply over 65% of the world’s electrical

energy needs. They are converted to electrical energy by steam turbine

generators and large scale fossil fuelled plants before distribution via the

electrical power grid. Since fossil fuels are non-renewable energy sources, they

are considered gone once they are used up because it will take millions of years

to replenish them. (Electricity Generation from Fossil Fuels, Retrieved from

http://www.mpoweruk.com/fossil_fuels.htm)

Due to our reliance to fossil fuels, a lot has been already said about

shifting from non-renewable resources to renewable resources, especially solar

energy. American inventor and businessman Thomas Edison (1931) said, “I'd

put my money on the sun and solar energy. What a source of power! I hope we

don't have to wait until oil and coal run out before we tackle that.” In one of her

speeches, Senator Hillary Clinton (2005) stated, “Clearly, we need incentives to

quickly increase the use of wind and solar power; they will cut costs, increase our

energy independence and our national security and reduce the consequences of

global warming.” Even Nobel Prize in Chemistry (1967) awardee Sir George

Porter remarked that, “I have no doubt that we will be successful in harnessing

the sun's energy... If sunbeams were weapons of war, we would have had solar

energy centuries ago.”

The Report of the Basic Energy Sciences Workshop on Solar Energy

Utilization (2015) states that the sunlight received by the Earth in one hour (4.3 ×

1020 J) is more than all the energy consumed on the planet in a year (4.1 × 1020

J). Yet, in 2001, solar electricity only provided less than 0.1% of the world's

electricity needs. The huge gap between our present use of solar energy and its

enormous undeveloped potential defines a grand challenge in energy research.

Sunlight is a compelling solution to our need for clean, abundant sources of

energy in the future. It is readily available, secure from geopolitical tension, and

poses no threat to our environment through pollution or to our climate through

greenhouse gases.

According to Solar, an info book by The National Energy Education

Development Project (The NEED Project, 2014), photovoltaic or solar cells are

used to convert solar energy into direct current electricity using semiconducting

materials that exhibit the photovoltaic effect. A photovoltaic system employs solar

panels composed of a number of solar cells to supply usable solar power.

Electricity is produced when radiant energy from the sun strikes the solar cell,

causing the electrons to move around. The action of the electrons starts an

electric current.

Solar Photovoltaic Electricity Empowering the World by European

Photovoltaic Industry Association (EPIA) and Greenpeace (2011) mentions the

present status and the expected advancements of solar PV as an electricity

generator.

At the end of 2009 the world was running 23 GW of photovoltaic (PV)

electricity, the equivalent of 15 coal-fired power plants. At the end of 2010, this

number should reach more than 35 GW. The cost to produce solar power has

dropped by around 22% each time world-wide production capacity has doubled,

reaching an average generation cost of 15c€/KWh in EU. Average efficiencies of

solar modules have also improved a couple percentage points per year. The

most efficient crystalline silicon modules go to 19.5% in 2010 with a target of

23% efficiency by 2020, which will further lower prices.

Solar PV applications can be grid connected systems or stand-alone, off-

grid and hybrid systems. When a PV system is connected to the local electricity

network, any excess power that is generated can be fed back into the electricity

grid. The owner of the PV system is paid according to the law for the power

generated by the local electricity provider. This type of PV system is referred to

as being “on-grid”. On the other hand, off-grid PV systems have no connection to

an electricity grid. An off-grid system is usually equipped with batteries, so power

can still be used at night or after several days of low irradiation.

Example of an off-grid PV system is in consumer goods. PV cells are now

found in many everyday electrical appliances such as watches, calculators, toys,

and battery chargers. Services such as water sprinklers, road signs, lighting and

telephone boxes also often rely on individual PV systems.

In his white paper Photovoltaic Power Systems, Dahl discusses the design

requirements in employing a remote power or off-grid power system. These

design requirements are solar panels, batteries, charge controller and inverter.

Solar panels charge the batteries, and the charge controller prevents the

batteries from being overcharged when there is abundant solar insolation

available. The batteries provide DC voltage to the inverter, and the inverter

converts the DC voltage to AC voltage for various loads.

In Design and Construction of Variable DC Source for Laboratory Using

Solar Energy, Hnin Mar Wai and Zaw Min Min Htun of Mandalay Technological

University design and construct a variable DC power supply for laboratory using

switch mode DC to DC converter. In their design, 80W solar panel is used which

has 17.6V and 4.55A. Using a charge controller, voltage is charged into 12V

battery which is used as the source for the DC to DC converter. The regulated

power of the variable output voltage ranges from 0 to 36 V with a maximum

output current of 3A. The variable DC power supply is based on the step-down

and step-up output voltage process which use both buck and boost converter

topologies. A switching converter comprise of capacitors, an inductor, a diode

and a switch. A microcontroller is used to control output voltage for precision and

stability. The output voltage and duty cycle is displayed with LCD display.

Chapter 3

Theoretical Framework

This chapter discusses the founding theories and principles of the project

to provide an understanding of the operation of the different parts of the system.

Linear Series

Regulator

Variable DC

(0 - 50V)

Inverter

AC Regulator

Variable AC

(0 - 50V)

Buck Converter

USB Port

(Fixed 5V DC)

Battery Bank (Lead-Acid Batteries)

Input

(Sunlight)

Solar Panel

SOLAR CHARGER

Voltage Regulator

Boost Converter

MCU (Gizduino

ATMega328) LCD

Battery

The diagram shows the building blocks in the design of the solar

independent power supply that outputs an adjustable AC and DC voltage of 0 to

40V and a constant 5V DC for charging portable devices via a USB port. The

system is divided into two modes: charging mode and power supply mode.

During charging mode, the power discharged by the battery bank is replenished

by harnessing solar energy into electricity. In power supply mode, the battery

bank is used as the power source to produce the necessary AC and DC output.

In charging mode, the solar panel converts solar light energy or sunlight

into direct current voltage or electricity. This voltage is feed into the solar charger

circuit composed of a voltage regulator and a boost converter. The voltage

regulator is used to maintain a fixed voltage output regardless of the varying

amount of electricity produced by the solar panel due to the changing amount of

sunlight that it absorbs. The boost converter amplifies the fixed voltage output

from the voltage regulator to obtain sufficient voltage to charge the battery bank.

During power supply mode, the battery bank supplies three different

circuits depending on the desired output: the linear series regulator for adjustable

DC, the inverter and AC regulator for adjustable AC and the buck converter for

charging portable devices. The linear series regulator operates by using a

variable resistance element to change the value of the output voltage, thus

resulting to an adjustable DC output. The inverter converts the DC voltage from

the battery into AC voltage then feeds the output to an AC regulator to obtain

variable AC voltage. The buck converter down converts the higher battery bank

voltage into 5V to match the charging voltage of portable devices.

Solar Charger

A solar charger employs solar energy to supply electricity to devices or

charge batteries. They can charge lead acid or nickel-cadmium (Ni-Cd) battery

bank up to 48V and hundreds of ampere-hours (up to 400Ah) capacity. For such

type of solar chargers, charge controllers are used and solar panels are

connected to the battery bank.

A solar panel can produce a range of charging voltages depending upon

sunlight intensity, so a voltage regulator must be included in the charging circuit

so as to not over drive (over voltage) a device such as a twelve-volt battery.

Lead Acid Battery

All lead acid batteries consist of flat lead plates immersed in a pool of

electrolyte. Regular water addition is required for most types of lead acid

batteries although low-maintenance types come with excess electrolyte

calculated to compensate for water loss during a normal lifetime.

A battery cell consists of two lead plates: a positive plate covered with a

paste of lead dioxide and a negative made of sponge lead, with an insulating

material (separator) in between. The plates are enclosed in a plastic battery case

and then submersed in an electrolyte consisting of water and sulfuric acid. Each

cell is capable of storing 2.1 volts.

In order for lead acid cell to produce a voltage, it must first receive a

(forming) charge voltage of at least 2.1 volts/cell from a charger. Lead acid

batteries do not generate voltage on their own; they only store a charge from

another source. This is the reason lead acid batteries are called storage

batteries, because they only store a charge. The size of the battery plates and

amount of electrolyte determines the amount of charge lead acid batteries can

store. The size of this storage capacity is described as the amp hour (Ah) rating

of a battery. Lead acid batteries can be connected in parallel to increase the total

Ah capacity.

Figure 1. Lead Acid Battery Cell

In figure 2, a 12.6 volts fully charged battery is connected to a load (light

bulb) and the chemical reaction between sulfuric acid and the lead plates

produces the electricity to light the bulb. This chemical reaction also begins to

coat both positive and negative plates with a substance called lead sulfate, also

known as sulfation (shown as a yellow build-up on plates). This build-up of lead

sulfate is normal during a discharge cycle. As the battery continues to

discharge, lead sulfate coats more and more of the plates and battery voltage

begins to decrease from fully charged state of 12.6 volts.

In figure 3, the battery is now fully discharged, the plates are almost

completely covered with lead sulfate (sulfation) and voltage has dropped to 10.5

volts. Lead sulfate (sulfation) now coats most of the battery plates. Lead sulfate

is a soft material which can be reconverted back into lead and sulfuric acid,

provided the discharged battery is immediately connected to a battery charger. If

a lead acid battery is not immediately recharged, the lead sulfate will begin to

Figure 2. 12.6V Lead Acid Battery Powering a Light Bulb

form hard crystals, which cannot be reconverted by a standard fixed voltage

(13.6 volts) battery charger.

In order to recharge a 12-volt lead acid battery with a fully charged

terminal voltage of 12.6 volts, the charger voltage must be set at a higher

voltage. Most chargers on the market are set at approximately 13.6 volts. During

the battery recharge cycle lead sulfate (sulfation) begins to reconvert to lead and

sulfuric acid. As shown in figure 4 below, the discharged battery is connected to

a charger with its output voltage set at 13.6 volts.

Figure 3. 12.6V Lead Acid Battery Discharged to 10.5V

Figure 4. 12.6V Lead Acid Battery Connected to 13.6V

charger

During the recharging process, as electricity flows through the water

portion of the electrolyte and water, (H2O) is converted into its original elements,

hydrogen and oxygen. These gasses are very flammable and the reason lead

acid batteries must be vented outside. Gassing causes water loss and therefore

lead acid batteries need to have water added periodically. Sealed lead acid

batteries contain most of these gasses allowing them to recombine into the

electrolyte. If the battery is overcharged, pressure from these gasses will cause

relief caps to open and vent, resulting in some water loss. Most sealed batteries

have extra electrolyte added during the manufacturing process to compensate for

some water loss.

The battery shown in figure 5 has been fully recharged using a fixed

charging voltage of 13.6 volts. Notice that some lead sulfate (sulfation) still

remains on the plates. This build-up will continue after each recharging cycle and

gradually the battery will begin to loose capacity to store a full charge and

eventually must be replaced. Lead sulfate build up is reduced if battery is given

an equalizing charge. An equalizing charge increases charging voltage to 14.4

volts. This higher voltage causes gassing that equalizes (re-mixes) the electrolyte

solution.

The following factors are considered in the selection of batteries for PV

applications:

Deep discharge (70–80% depth discharge)

Low charging - discharging current

Long-duration charge (slow) and discharge (long duty cycle

Irregular and varying charge and discharge rate

Low self-discharge

Long lifetime

Less maintenance requirement

High energy storage efficiency

Low cost

Figure 5. Gassing in the Lead Acid Battery

Linear Power Supplies

A linear regulated power supply regulates the output voltage by dropping

excess voltage in a dissipative component. They use a moderately complex

regulator circuit to achieve very low load and line regulation. Linear regulated

power supplies also have very little ripple and very little output noise.

Linear power supplies gain their name from the fact that they use linear,

i.e. non-switching techniques to regulate the voltage output from the power

supply. The term linear power supply implies that the power supply is regulated

to provide the correct voltage at the output. Sometimes the sensing of the voltage

may be accomplished at the output terminals, or on some occasions it may be

achieved directly at the load. There are two main types of linear power supply:

series regulator and shunt regulator.

The series voltage regulator format or as it is sometimes called the series

pass regulator is the most commonly used format for providing the final voltage

regulation in a linear voltage regulator circuit. As the name suggests, the series

voltage regulator or series pass voltage regulator operates by using a variable

element in series with the load. By changing the resistance of the series element,

the voltage dropped across it can be varied to ensure that the voltage across the

load remains constant. The advantage of the series voltage regulator is that the

amount of current drawn is effectively used by the load, although some will be

consumed by any circuitry associated with the regulator. Unlike the shunt

regulator, the series regulator does not draw the full current even when the load

does not require any current. As a result the series regulator is considerably

more efficient.

Although the shunt voltage regulator is not widely used to provide the

main regulation in many applications, it nevertheless finds uses in many other

areas of circuitry. Essentially the load is operated with a resistor in series with the

voltage source and the shunt regulator then in parallel with the load. In order to

keep the voltage across the load constant, a level of current must be drawn

through the series resistor to maintain the required voltage across the load. The

load will take some and the remaining current is drawn by the shunt voltage

regulator. The circuit is designed so that at maximum load current the shunt

regulator draws virtually no current and at minimum load current, the shunt

voltage regulator passes the full current. As a result, it can be seen that shunt

regulators are inefficient because maximum current is drawn from the source

regardless of the load current, i.e. even when there is no load current.

While linear power supplies may not be as efficient as other types of

power supply technology, they offer the best performance and are therefore used

in many applications where noise is of great importance. Often audio amplifiers

and many other items of electronic equipment use linear power supplies to obtain

the best performance.

The use of any technology is often a careful balance of several

advantages and disadvantages. This is true for linear power supplies which offer

some distinct advantages, but also have their drawbacks.

The advantages of linear power supplies are low noise and its reputation

as an established technology. The use of the linear technology without any

switching element means that noise is kept to a minimum and the annoying

spikes found in switching power supplies are not found. It has also been in

widespread use for many years and their technology is well established and

understood.

On the other hand, efficiency, size and dissipation are the disadvantages

of linear power supplies. In view of the fact that a linear power supply uses linear

technology, it is not particularly efficient. Efficiencies of around 50% are not

uncommon, and under some conditions they may offer much lower levels. The

use of linear technology means that the size of a linear power supply tends to be

larger than other forms of power supply. The use of a series or parallel (less

common) regulating element means that significant amounts of heat are

dissipated and this needs to be removed.

Despite the disadvantages, linear power supply technology is still widely

used; although it is more widely used where low noise and good regulation is

needed. Typical applications of linear regulated power supplies

include but are not limited to the following:

Low noise amplifiers

Signal processing

Data acquisition - including sensors, multiplexers, A/D converters, and

sample & hold circuits.

Automatic test equipment

Laboratory test equipment

Control circuits

Anywhere that excellent regulation and/or low ripple is required

Switched Mode Power Supplies

A switched-mode power supply (switching-mode power supply, switch-

mode power supply, SMPS, or switcher) is an electronic power supply that

incorporates a switching regulator to convert electrical power efficiently. Like

other power supplies, an SMPS transfers power from a source, like mains power,

to a load, such as a personal computer, while converting voltage and current

characteristics. Unlike a linear power supply, the pass transistor of a switching-

mode supply continually switches between low-dissipation, full-on and full-off

states, and spends very little time in the high dissipation transitions, which

minimizes wasted energy. Ideally, a switched-mode power supply dissipates no

power. Voltage regulation is achieved by varying the ratio of on-to-off time. In

contrast, a linear power supply regulates the output voltage by continually

dissipating power in the pass transistor. This higher power conversion efficiency

is an important advantage of a switched-mode power supply. Switched-mode

power supplies may also be substantially smaller and lighter than a linear supply

due to the smaller transformer size and weight.

The main advantage of the switching power supply over linear power

supply is greater efficiency because the switching transistor dissipates little

power when acting as a switch. Other advantages include smaller size and

lighter weight from the elimination of heavy line-frequency transformers, and

lower heat generation due to higher efficiency. Disadvantages include greater

complexity, the generation of high-amplitude, high-frequency energy that the low-

pass filter must block to avoid electromagnetic interference (EMI), a ripple

voltage at the switching frequency and the harmonic frequencies thereof.

There are several topologies commonly used to implement SMPS. Any

topology can be made to work for any specification; however, each topology has

its own unique features. SMPS can be buck, boost or buck-boost type.

Buck Converter

A buck converter is a voltage step down and current step up converter.

The simplest way to reduce the voltage of a DC supply is to use a linear

regulator, but linear regulators waste energy as they operate by dissipating

excess power as heat. Buck converters, on the other hand, can be remarkably

efficient (95% or higher for integrated circuits), making them useful for tasks such

as converting the main voltage in a computer (12 V in a desktop, 12 – 24 V in a

laptop) down to the 0.8 – 1.8 volts needed by the processor.

The buck converter is used in SMPS circuits where the DC output voltage

needs to be lower than the DC input voltage. The DC input can be derived from

rectified AC or from any DC supply. It is useful where electrical isolation is not

needed between the switching circuit and the output, but where the input is from

a rectified AC source, isolation between the AC source and the rectifier could be

provided by a mains isolating transformer.

The switching transistor between the input and output of the buck

converter continually switches on and off at high frequency. To maintain a

continuous output, the circuit uses the energy stored in the inductor, during the

on periods of the switching transistor, to continue supplying the load during the

off periods. The circuit operation depends on what is sometimes also called a

flywheel circuit. This is because the circuit acts rather like a mechanical flywheel

that, given regularly spaced pulses of energy keeps spinning smoothly

(outputting energy) at a steady rate.

Figure 6. Basic Buck Converter Circuit

Boost Converter

A boost converter (step-up converter) is a DC-to-DC power converter with

an output voltage greater than its input voltage. It is a class of switched-mode

power supply containing at least two semiconductors (a diode and a transistor)

and at least one energy storage element, a capacitor, inductor, or the two in

combination. Filters made of capacitors (sometimes in combination with

inductors) are normally added to the output of the converter to reduce output

voltage ripple.

Switched mode supplies can be used for many purposes including DC to

DC converters. Often, although a DC supply, such as a battery may be available,

its available voltage is not suitable for the system being supplied. For example,

the motors used in driving electric automobiles require much higher voltages, in

the region of 500V, than could be supplied by a battery alone. Even if banks of

batteries were used, the extra weight and space taken up would be too great to

be practical. The answer to this problem is to use fewer batteries and to boost

the available DC voltage to the required level by using a boost converter. Another

problem with batteries, large or small, is that their output voltage varies as the

available charge is used up, and at some point the battery voltage becomes too

low to power the circuit being supplied. However, if this low output level can be

boosted back up to a useful level again, by using a boost converter, the life of the

battery can be extended.

The DC input to a boost converter can be from many sources as well as

batteries, such as rectified AC from the mains supply, or DC from solar panels,

fuel cells, dynamos and DC generators. The boost converter is different to the

buck converter in that its output voltage is equal to, or greater than its input

voltage. However it is important to remember that, as power (P) = voltage (V) x

current (I), if the output voltage is increased, the available output current must

decrease.

Figure 7 below illustrates the basic circuit of a boost converter. However,

in this example the switching transistor is a power MOSFET, both bipolar power

transistors and MOSFETs are used in power switching, the choice being

determined by the current, voltage, switching speed and cost considerations. The

rest of the components are the same as those used in the buck converter

illustrated in figure 6 except that their positions have been rearranged.

Figure 7. Basic Boost Converter Circuit

Inverter

A power inverter, or inverter, is an electronic device or circuitry that

changes direct current (DC) to alternating current (AC). The inverter does not

produce any power; the power is provided by the DC source.

To produce AC voltage, some inverters use electromagnetic switches that

flick on and off at high speed to reverse the current direction. Inverters like this

often produce what's known as a square-wave output: the current is either

flowing one way or the opposite way or it's instantly swapping over between the

two states:

These kind of sudden power reversals are quite brutal for some forms of

electrical equipment. In normal AC power, the current gradually swaps from one

direction to the other in a sine-wave pattern, like this:

Figure 8. Square Wave

Figure 9. Sine Wave

Electronic inverters can be used to produce this kind of smoothly varying

AC output from a DC input. They use electronic components called inductors

and capacitors to make the output current rise and fall more gradually than the

abrupt, on/off-switching square wave output from a basic inverter.

Inverters can also be used with transformers to change a certain DC input

voltage into a completely different AC output voltage (either higher or lower) but

the output power must always be less than the input power: it follows from

the conservation of energy that an inverter and transformer can't give out more

power than they take in and some energy is bound to be lost as heat as

electricity flows through the various electrical and electronic components. In

practice, the efficiency of an inverter is often over 90%.

A typical power inverter device or circuit requires a relatively stable DC

power source capable of supplying enough current for the intended power

demands of the system. The input voltage depends on the design and purpose of

the inverter. Examples include:

12V DC, for smaller consumer and commercial inverters that typically run

from a rechargeable 12V lead acid battery.

24 and 48V DC, which are common standards for home energy systems

200 to 400V DC, when power is from photovoltaic solar panels

300 to 450V DC, when power is from electric vehicle battery packs in

vehicle-to-grid systems

Hundreds of thousands of volts, where the inverter is part of a high voltage

direct current power transmission system

For battery-powered inverter, the runtime of an inverter is dependent on

the battery power and the number of plugs utilizing the inverter at a given time.

As the amount of equipment utilizing the inverter increases, the runtime will

decrease. In order to prolong the runtime of an inverter, additional batteries can

be added to the inverter.

When attempting to add more batteries to an inverter, there are two basic

options for installation: series configuration and parallel configuration. If the goal

is to increase the overall voltage of the inverter, batteries can be daisy-chained

into a series configuration. In a series configuration, if a single battery dies, the

other batteries will not be able to power the load. On the other hand, if the goal is

to increase capacity and prolong the runtime of the inverter, one can connect

batteries in a parallel configuration. In a parallel configuration, if a single battery

dies, the other batteries will be able to power the load.

AC Regulator (DIAC and TRIAC Phase Control)

A voltage regulator is designed to automatically maintain a constant

voltage level. Depending on the design, it may be used to regulate one or more

AC or DC voltages.

Phase control is often used in AC power supplies to control the amount of

voltage, current or power that is fed to its load. It does this in much the same way

that a pulse-width modulated (PWM) supply would pulse on and off to create an

average value at its output. If the supply has a DC output, its time base is of no

importance in deciding when to pulse the supply on or off, as the value that will

be pulsed on and off is continuous.

Phase control differs from PWM in that it addresses supplies that output a

modulated waveform, such as the sinusoidal AC waveform that the national grid

outputs. Here, it becomes important for the supply to pulse on and off at the

correct position in the modulation cycle for a known value to be achieved; for

example, the controller could turn on at the peak of a waveform or at its base if

the cycle's time base were not taken into consideration.

Phase control works by modulating a thyristor, SCR (silicon controlled

rectifier), TRIAC (triode for alternating current), thyratron, or other such gated

diode-like devices into and out of conduction at a predetermined phase of the

applied waveform. Example of a phase control circuit is that of a DIAC and

TRIAC phase control.

The basic full-wave TRIAC phase control circuit shown in figure 10 above

requires only five components: resistor, adjustable resistor, capacitor, DIAC and

TRIAC. Adjustable resistor R1 and C1 are a single-element phase shift network.

When the voltage across C1 reaches breakover voltage of the DIAC, C1 is

partially discharged by the DIAC into the TRIAC gate. The TRIAC is then

triggered into conduction mode for the remainder of that half-cycle. The unique

simplicity of this circuit makes it suitable for applications with small control range.

DIACs are often used in conjunction with TRIACs because these TRIACs

do not fire symmetrically as a result of slight differences between the two halves

of the device. This results in harmonics being generated and the less

Figure 10. DIAC and TRIAC Phase Regulator

symmetrical the device fires, the greater the level of harmonics produced. It is

generally undesirable to have high levels of harmonics in a power system.

To help in overcoming this problem, a DIAC is often placed in series with

the gate. This device helps make the switching more even for both halves of the

cycle. This results from the fact that its switching characteristic is far more even

than that of the TRIAC. Since the DIAC prevents any gate current flowing until

the trigger voltage has reached a certain voltage in either direction, this makes

the firing point of the TRIAC more even in both directions.

Microcontroller Unit (GIZDUINO ATMega328)

A microcontroller is a compact microcomputer designed to govern the

operation of embedded systems in motor vehicles, robots, office machines,

complex medical devices, mobile radio transceivers, vending machines, home

appliances, and various other devices. A typical microcontroller includes a

processor, memory, and peripherals.

The simplest microcontrollers facilitate the operation of the

electromechanical systems found in everyday convenience items. Originally,

such use was confined to large machines such as furnaces and automobile

engines to optimize efficiency and performance. In recent years, microcontrollers

have found their way into common items such as ovens, refrigerators, toasters,

clock radios, and lawn watering systems. Microcomputers are also common in

office machines such as photocopiers, scanners, fax machines, and printers.

The microcontroller was used to program the liquid crystal display to show

the different important instructions and warning in using the power supply.

Chapter 4

Methodology

This chapter enumerates the procedures applied in the design and

construction of the prototype solar powered AC and DC power supply. It also

specifies the methods of data collection and of the statistical treatment of the

data gathered.

CONCEPTUALIZATION OF THE PROJECT

ACQUISITION OF MATERIALS

ASSESMENT OF THE SYSTEM

STATISTICAL ANALYSIS OF DATA

CONSTRUCTION OF THE SYSTEM

PROTOTYPING

TROUBLESHOOTING

Conceptualization of the Project

The preliminary schematic diagram of the project was designed by using

the groundwork obtained from the review of related literature and theoretical

framework. The schematic diagram was simulated using Proteus until the

objective of the project was achieved.

Acquisition of Materials

The materials needed for the construction of the project are solar panel,

solar charger circuit, battery bank, linear regulator circuit, inverter, AC regulator,

buck converter circuit, USB port, microcontroller unit, LCD and casing. This also

included all the circuit components and equipment necessary to assemble the

system. Unavailable or expensive circuit components were replaced with similar

or alternative ones.

Construction of the System

First, a breadboard prototype of the system was constructed to test the

real-life response of the circuit compared to that of the simulated version.

Necessary adjustments were made until the preliminary prototype meets the

objectives of the project. Next, the necessary circuitry to connect the hardware

part to the software part was built. Then the final prototype of the system was

assembled. Lastly, the prototype was tested again before it was packaged in a

presentable casing.

Assessment of the System

The setup was verified by testing it to a circuit to check that the voltage

range in the objectives was achieved. The project was also tested for output

voltage stability and voltage regulation. The individual efficiencies of the AC and

DC supply and their overall efficiency was also computed.

To test for the output voltage stability, the output voltage of the unloaded

DC supply was observed for a period of two hours. Output voltage readings were

recorded every twenty (20) minutes. For the AC supply, the output voltage was

observed for a period of one hour with output voltage readings recorded every

ten (minutes). The input voltage from the battery was also recorded at the same

time with the output voltage readings for both DC and AC power supplies. This

was to check that the battery can output a stable voltage over an extended

period of time base on its discharge rate.

To test the DC supply voltage regulation, a 5kΩ potentiometer was

connected in series with the power supply as a test load. On the other hand, a

20k potentiometer in series connection with the power supply was used to

assess the voltage regulation of the AC supply. The values of the load

resistances were based on different research journals doing the same project

concept. The lowest test value was the resistance of the potentiometer where

there was still an output reading while the largest value was based on the voltage

regulation percentage industry tolerance of 5%. The resistance values per trial

were incremented 50Ω for DC supply and 500Ω for AC supply.

The individual efficiencies of the DC and AC power supply were

determined by computing the ratio of the output voltage over the input voltage at

50% regulation. The values at 50% regulation were used because it is the

standard followed by the industry.

Statistical Analysis of Data

The data gathered from the voltage stability test was subjected to

standard deviation. Standard deviation was used to get the amount of voltage

that the measured output voltage will vary with respect to the expected output

voltage over the set period of the power supply operation per class. The data

from battery discharge rate and voltage regulation was subjected to descriptive

method with respect to known standards for power supplies.

Chapter 5

Technical Study

This chapter covers the working methods that will be used to achieve the

objectives of the project which includes the project description, project design,

design considerations, design specifications, design computation, program and

system flowchart, programming tools, component selection and power supply

specifications.

.

Project Description

This project utilized solar light energy collected by photovoltaic cells in a

solar panel to store charge in the sealed lead-acid batteries. The power from the

batteries was used to get the desired adjustable DC and AC voltage output and

to charge phones and other portable devices. The DC and AC voltage value can

be varied from 0 to 50 volts while the charger outputted a constant 5 volts in DC

via a universal serial bus port.

The device was designed to be purely solar independent, thus the

exclusion of using the 220V AC mains outlet as an alternative to charge the

batteries. The solar panel was detachable from the power supply to lessen the

bulk and weight of the system. This increased ease of use by making the power

supply portable and with the solar panel being less of a hassle during

experiments. Toggle switches were used to mechanically switch the batteries

between charging mode (batteries in 12V parallel connection) to power supply

mode (batteries in 48V series connection). Since the solar panel had a maximum

output of 20V, connecting the batteries in parallel ensured that the voltage of the

batteries (12V) can be charged within the voltage capability of the solar panel.

On the other hand, connecting the batteries in parallel (48V) enabled the system

to reach the required AC and DC output voltage range.

Project Design

Figure 11. 3D Design of the Prototype Project

The casing of the prototype power supply was engineered with reference

to existing power supplies for laboratory use. The casing used metal sheets to

increase durability with proper grounding to prevent electric shock. The design

was kept as compact as possible while providing enough space to house the

batteries, electronic circuitries, and wirings. The back side of the casing has

punched holes for proper ventilation to prevent overheating during the operation

of the device. The front side was the location of the display of the specifics of the

power supply, mains switch (rocker switch) for AC (right side) and DC (left side),

output terminal of the AC (right side) and DC (left side) and a tuner for the

desired AC and DC voltage level. The left side was the location of the toggle

switches to switch the device from charging mode to power supply mode and

vice versa, the rocker switch for turning the solar charger on/off and the input

terminals for the solar panel.

Design Considerations

I. Voltage Range

Voltage range is the area of variation between the upper and lower limits

of the power supply output. Since the power supply was intended for laboratory

use, the prototype was designed in accordance to the laboratory power

requirements at the Department of Electronics Engineering, College of

Engineering and Architecture, Bataan Peninsula State University - Main Campus.

The laboratory experiments for ECE students uses the LabVolt Manual

(Volumes l, ll, lll, and lV) with activities from the following subjects: Circuits l

(Elementary Electrical Circuits), Circuits ll (Electrical Circuits 2), Electronics l,

Electronics ll, Electronics lll, and Electronics V (Industrial Electronics). Based

from the laboratory requirements, the maximum DC voltage used was 40V and

the minimum voltage was 6V while the maximum AC voltage used was 40V and

the minimum AC voltage was 6.3V. The voltage range to be used for both AC

and DC will have a range of 0 to 40V.

LABORATORY EXERCISES (DC SOURCE)

CIRCUITS

Voltage

(volts)

Current

(amps)

Power

(watts)

SAFETY: USE OF SOURCES AND METERS 6 0.01 0.06

THE ELECTRONIC VOM 10 0.01 0.1

THE ELECTRONIC POWER SUPPLY 40 0.5 20

OHM’S LAW 30 0.025 0.75

POWER - HEAT – LIGHT 10 0.25 2.5

SERIES RESISTIVE CIRCUITS 25 0.25 6.25

SERIES CIRCUIT- KIRCHHOFF’S LAW 30 0.005 0.15

THE ELECTRONIC POWER SUPPY 40 0.25 10

ELECTRONICS

Voltage

(volts)

Current

(amps)

Power

(watts)

ZENER DIODE VOLTAGE REGULATION 40 0.1 4

COMMON BASE CIRCUIT 24 0.002 0.048

COMMON EMITTER CIRCUIT 24 0.002 0.048

COMMOM COLLECTOR CIRCUIT 24 0.002 0.048

RC COUPLING 24 0.002 0.048

INTRODUCTION TO SEMICONDUCTOR DIODES 40 0.01 0.4

INDUSTRIAL ELECTRONICS

Voltage

(volts)

Current

(amps)

Power

(watts)

SILICON CONTROLLED RECTIFIER (SCR) 6 0.15 0.9

SILICON CONTROLLED RECTIFIER GATE

CHARACTERISTICS

6 0.5 3

6 0.01 0.06

SILICON CONTROLLED RECTIFIER DC POWER

CONTROL 6 0.5 3

UNIJUNCTION TRANSISTOR (UJT) 10 0.02 0.2

UNIJUNCTION TRANSISTOR WAVEFORM

GENERATION 12 0.02 0.24

UNIJUNCTION TRANSISTOR – SCR TIME DELAY

CIRCUIT 12 0.5 6

TRIAC & DIAC

6 0.5 3

6 0.1 0.6

40 0.01 0.4

MINIMUM VALUE 6 0.002

MAXIMUM VALUE 40

LABORATORY EXERCISES (AC SOURCE)

ELECTRONICS

Voltage

(Volts)

Current

(Amps)

Power

(Watts)

RECTIFIERS, HALF-WAVE & FULL-WAVE 14 0.02 0.28

INDUSTRIAL ELECTRONICS

Voltage

(Volts)

Current

(Amps)

Power

(Watts)

SILICON CONTROLLED RECTIFIER GATE

CHARACTERISTICS 6.3 0.15 0.945

SILICON CONTROLLED RECTIFIER DC POWER

CONTROL 6.3 0.2 1.26

SILICON CONTROLLED RECTIFIER AC POWER

CONTROL 6.3 0.2 1.26

TRIAC & DIAC 6.3 0.5 3.15

TRIAC & DIAC AC POWER CONTROL 40 0.5 20

MINIMUM VALUE 6.3 0.02

MAXIMUM VALUE 40 0.5

II. Duration of Use

The duration of use of the power supply is the length of time that the

different outputs of the supply can be used when the batteries are fully charged.

The expected duration of use was based on the schedule of laboratory classes at

the Department of Electronics Engineering, College of Engineering and

Architecture, Bataan Peninsula State University - Main Campus.

The class period in the College of Engineering and Architecture was from

seven (7) o'clock in the morning to nine (9) o'clock in the evening which was

Table 1. Power Requirements in the Electronics Engineering Laboratory of

Bataan Peninsula State University

composed of fourteen (14) hours daily. The allocated time for every laboratory

subjects was three (3) hours, thus there were only four (4) laboratory subjects

that can be conducted daily. The maximum laboratory hours that can be

conducted daily in the Department of Electronics Engineering were only twelve

(12) hours.

Based on the laboratory schedules and the proponents own experience in

conducting experiments in BPSU, the power supply was designed to be used

daily for ten (10) hours for the DC output, six (6) hours for the AC output and one

and a half (1

) hours for the charger output. Thus, for each laboratory class, the

DC output can be used for 2

hours, the AC output for 1

hours and the charger

for about twenty (20) minutes. Significantly longer hours were allocated for DC

output because there were more experiments that used this kind of output (refer

to table 1). There were also times when the experiments conducted didn’t use

AC output at all. The charger output was only allotted twenty minutes so that

students will only use the charger when they really need to charge their portable

devices to search for datasheets, instructions and other research related to the

experiments. This was to discourage the students to use the charger for

extended periods of time and for personal use, especially if the need to charge

their portable devices was because they were texting, watching movies or

playing games in their gadgets instead of doing the experiments.

III. Power Requirement

Power requirement is the average power need to power the experiments

during duration of use of the laboratory activities. The data was based on the

power requirements in table 1.

DC POWER SOURCE

Power

Maximum Value 20W

Minimum Value 48mW

Average Power Usage 2.575W

Based from table 2, the minimum DC voltage in the laboratory was 6V DC

while the maximum DC voltage was 40V DC. Using the formula for getting the

average for ungrouped data:

∑

Where:

= average value

t = power usage in the laboratory

= number of laboratory activities

Table 2. DC Power Consumption

( ) ( )

The average power usage in the laboratory experiments for DC voltage

was 2.575 watts.

AC POWEER SOURCE

Power

Maximum Value 20W

Minimum Value 280mW

Average Power Usage 3.842W

Based from table 3, the minimum AC voltage in the laboratory was 6.3V

AC while the maximum AC voltage was 40V AC. The average power usage was

computed using the formula for getting the average for ungrouped data.

( )

Table 3. AC Power Consumption

The average power usage for AC voltage was 3.842 watts. For USB

charger, the specification used was based on the standard which is 5V DC with

0.5V DC tolerance and with a current of 500mA that will produce a power

consumption of 2.5 watts. The total power loading that the designed power

supply must be able to carry was 52.552W-h daily (summation of the product of

DC and AC average power usage together with the charger power consumption

with the duration of usage).

Design Specifications

VOLTAGE

RANGE

DURATION

OF USE

POWER

REQUIREMENT

Per

Class

Per

Day

Average

Power Usage

Average Power Consumption

per Day

DC

OUTPUT

Adjustable

0 – 50 V

DC

2

hours

10

hours 2.575 watts

25.75 watt-hour

AC

OUTPUT

Adjustable

0 – 50 V

AC

1

hours

6

hours 3.842 watts

23.052 watt-hour

CHARGER

OUTPUT

Fixed 5V

DC

0.5V DC

tolerance

20

minutes

1.5

hours 2.5 watts

3.75 watt-hour

Overall Schematic Diagram

Fig

ure

12

. O

ve

rall

Sche

ma

tic D

iag

ram

of

the

So

lar

– P

ow

ere

d A

C/D

C P

ow

er

Sup

ply

fo

r E

lectr

on

ics E

ng

ine

erin

g

La

bo

rato

ry

Design Computation

I. Solar Charger

Fig

ure

13

. S

ch

em

atic D

iag

ram

of

the

So

lar

Ch

arg

er

tog

eth

er

with

the

Se

rie

s -

Pa

ralle

l

Con

ne

ctio

n o

f th

e B

atte

rie

s

Solar Panel

SOLAR INSOLATION LEVELS

City Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year

Avg

Cebu City

4.55 5.08 5.53 5.81 5.6 4.91 4.58 4.54 4.73 4.72 4.53 4.35 4.91

Manila 4.35 4.91 5.51 5.8 5.42 4.88 4.46 4.01 4.3 4.11 4.03 3.84 4.63

1. Values in kWh/m2/day

2. Source: NASA surface meteorology and solar energy. © 2012 Apricus Solar Co., Ltd. All rights reserved

The worst solar insolation in an area determines the minimum effective

daily charging time in that location. The solar insolation in Bataan is assumed to

be the same as that in Manila because it is hundreds of kilometres nearer

compared to Cebu City. The worst solar insolation is 3.84kWh/m2/day and it

occurs in December. Together with the daily power requirement of the system,

this solar insolation value will be used to solve for the number of 20-watts solar

panel required to charge the battery bank.

Solar Insolation x Solar Panel Power Rating = Harnessed Solar Power per Day

Table 4. Solar Insolation Level for Cebu and Manila

Thus,

= Number of Solar Panels

Battery

Panasonic Sealed Lead Acid battery with six (6) volts, 4.5Ah rating was

used in this design. The battery bank was set to be fully discharged after two

days of when used as specified in the duration of use. The following

computations showed how the batteries can meet the daily power consumption

of 52.552 watt-hours before it become fully discharged within two (2) days.

For the DC source:

For 6V, 4.5Ah

P = IV

( )( )

( )

For the AC Source and Charger:

( )

( )

The required voltage for the inverter to operate was only twelve (12) volts

and the maximum DC voltage range specified on the design consideration was

40V . Thus a minimum of seven (7) six - volt battery in series connection must be

used to produced the required output. In order to charged this batteries properly,

parallel configuration was used to meet the twelve (12) volts required by the

inverter and switching elements was used to charged the batteries for the DC

with additional one (1) battery. The output voltage of the charging circuit was set

to 14.4 volts to avoid lead sulfate build up mentioned on theoretical framework.

Since the LED can only handle a maximum of 30mA, a series resistor was added

to limit the current that will pass through the LED. This LED protection was

applied in the LED in the output of the regulator and in the LED in the output of

the charger.

Charging Time of the Battery

where:

Charging Current = 1.0A (Solar panel specification is 1.6A but the maximum

output current of the regulator is only 1.0A)

Battery Current Rating = 18Ah (4 branches with 4.5Ah each branch)

Considering Losses with the standard of forty percent (40%):

( )

II. Adjustable DC Stage

Eight (8) lead acid batteries were used to produce the maximum

voltage required in laboratory using linear series voltage converter.

Percentage Level of Batteries (%) Charging Time (h)

0 25.2

25 18.9

50 `12.6

75 6.3

Table 5. Charging Time Table

The circuit above could generate a maximum DC voltage of 50 volts that

could deliver 2A current. The 40 volts was within the maximum output voltage

thus achieving the stated objective. The voltage was varied by adjusting the

resistance value of the potentiometers RV1 and RV2. Increasing the resistance

on RV1 decreased the voltage output with respect to Ohm's Law (resistance and

voltage is inversely proportional with each other) while increasing the value of

RV2 increased the value of the output because the output was parallel with the

Figure 14. Schematic Diagram of Adjustable DC Stage

RV2 (the higher the resistance the lower the voltage that will pass through the

RV2). The figure below showed the effect of varying the two variable resistors to

the output voltage. When RV1 was set to 0Ω, the resistor became shorted thus

the output will be purely dependent with the resistance of RV2. When RV2 was

set to 0Ω, the output voltage was the forward voltage drop in the LED. The output

voltage can computed using Kirchhoff's voltage law (the sum of all the voltages

around the loop is equal to zero).

At no load condition, the output voltage can be determined at RV1 set to

minimum and RV2 set to maximum:

:

(a.) (b.) (c.)

Figure 15. The schematic representation of the: (a.) output stage of the adjustable

DC, (b.) At RV1 minimum and RV2 was set to maximum, and (c.) At

RV2 minimum and RV1 was set to maximum

Thus,

At RV2 set to minimum and RV1 set to maximum, the output voltage will

be the forward voltage drop of the LED which was approximately 0.7 volts.

The maximum voltage was set to 40 volts with the R5 and R6 through the

LM317. LM317 was a monolithic integrated circuit which is an adjustable linear

series voltage regulator with three (3) – terminal, positive - voltage regulator

designed that can supply more than 1.5A of load current with an output voltage

adjustable over a 1.2V to 37V range. It employs internal current limiting, thermal

shutdown, and safe area compensation.

The designation of values for R5 and R6 to produce the maximum output

voltage of 40V was derived from the equation given on the manufacturer’s

datasheet.

(

)

Iadj was controlled to less than 100µA,

(

) ( )

III. Adjustable AC Stage

An inverter was used to convert the DC voltage into AC voltage. Inside the

inverter was the buck converter that step down the 12V DC voltage to 5V DC

output on the universal serial bus output terminal. The AC waveform from the

inverter was phase shifted by the R3 and RV1 with C1 so that reduced

amplitude, phase delayed version of the AC waveform appears across C1.

When the amplitude across C1 reaches the breakover voltage of the DIAC, the

capacitor will discharge through the DIAC, thus also triggering the TRIAC into

Figure 16. Schematic Diagram of Adjustable AC Stage with the Charger

conduction. The TRIAC will conduct for the remainder of the AC waveform of the

half cycle, then turning off once zero voltage was reached. The process was

repeated for every cycle, only changing the polarity of the DIAC to be triggered

into conduction. As the resistance of RV1 was varied, the amount of phase delay

in the waveform across the capacitor also varies. This allowed the time during

each half cycle to control the firing time of the TRIAC and in turn the amount of

power delivered to the load can be varied. When the resistance of the

potentiometer was set to zero, the amplitude of the AC will peak to its maximum

value. The transformer will down convert the regulated AC waveform into the

maximum 50V in accordance to the maximum voltage required on the laboratory.

Programming Tools

The purpose of the microcontroller was to command the liquid crystal

display to give warning and important instruction in using the power supply.

(a.)

(b.)

(c.)

Figure 17. (a.) Circuit, (b.) Block Diagram of the Gizduino, and (c.) Schematic Diagram of the Microcontroller Unit

System Flowchart

Component Specification

SOLAR CHARGER

COMPONENT DESCRIPTION USAGE

Solar Panel

Power = 20 Watts

Current = 1.16A

Voltage = 17.6 Pmax

Open Circuit Voltage = 21 V

Converts solar light energy to

direct current voltage

Energy source of the power

supply

Battery

Panasonic Sealed Lead

Acid Battery

Voltage = 6V

Ampere Rating = 4.5AH

Stores the charge generated by

the solar panel

Power source of the power

supply

START

“USE 50V MAX -->FOR DC ONLY!”

“SOLAR POWERED POWER SUPPLY”

“USE 12V MAX -->FOR AC ONLY!”

END

7805

LM7805 IC

(Positive Voltage Regulator)

Can deliver up to 1.5 A of

output current

Regulates the varying DC voltage

from the solar panel to have a

stable DC output from the

converter

C1, C2 220µF electrolytic capacitor

Blocks ripple voltage from

entering the regulator

Filters DC voltage to have an

output with low ripple voltage

R1, R2 1.0kΩ resistor Current limiter for red LED

D4 Red LED

Indicates if the output of the solar

panel is enough or is entering the

charger circuit

R3 470Ω resistor Voltage limiter for analog input

port 2 on the microcontroller

Boost

Converter

eDC-2420 Step Up DC/DC converter can generate up to 24VDC output from a single +5V input. Available output power ranges from 2.5W with 5.0V input, rising in proportion to the input up to 7.5W at +12V input.

Increases the voltage from the regulator to 14.4V to charge the batteries. Boost converter will work with up to +12VDC input. Higher input voltage correspondingly results in increased output wattage reserve. Based from the technical manual, the converter has 4W when operated with +12VDC input.

C3 220µF electrolytic capacitor

Filters DC voltage to have an

output with low ripple voltage and

noise

D1, D2

1N5402 Diode

(Blocking Diode)

Blocking Voltage = 200V

Non−Repetitive Peak

Reverse Voltage = 300V

Average Rectified Forward

Current = 3A

Ensures that if there was low or

no voltage coming from the solar

panel the voltage from the battery

will be blocked from entering the

converter and regulator to

prevent damaging the

components

R4, R5 22kΩ and 2.2kΩ resistor

(Voltage Divider Network)

Ensures that the voltage entering

the analog input port 0 is within

the range of 0 - 5V

D3 Green LED Indicates if there is an output in

the charger

ADJUSTABLE DC SUPPLY

COMPONENT DESCRIPTION USAGE

Q1 TIP42C

Increases the voltage and current

capacity of LM317 using power

amplifier configuration with R4 and

R5

R4, R3 3.9Ω, 22Ω Limits the current that will pass

through the LM317 regulator

C1 100µF Filters ripple voltage to prevent

damage to DC components

U1 LM317 IC

(Adjustable Regulator)

Regulates the desired DC voltage

output and

R5, R6 6.8KΩ, 220Ω resistors Produces the required output of

the LM317

C2 10µF electrolytic capacitor

(Bypass Capacitor)

Ensures that ripple voltage will be

grounded and would not sum up

with the DC output

D1 1N4004 Diode

(Clamp Diode)

Protects the regulator from output

polarity reversals during start-up

and short-circuit operation

C3,C4 0.01µF, 220µF electrolytic

capacitor

Improves transient response of the

circuit

R7 4.7kΩ resistor Serves as current limiting resistor

for load protection

RV1, RV2 250kΩ resistor Adjusts the output voltage to get

desired value

D2 Green LED

Indicates whether the circuit is

operational and if the voltage is

reaching the output stage

ADJUSTABLE AC SUPPLY

COMPONENT DESCRIPTION USAGE

Inverter

Power Rating = 100W

Input Voltage = 12V DC

Output Voltage = 220V AC

Converts the DC to AC waveform

R3 10kΩ potentiometer Reduces the amplitude of the AC

from the inverter

RV1 500kΩ potentiometer Controls the amplitude of the AC

waveform received by the R3

D3 Diac

(Diode for AC)

Triggers the triac to conduction

mode

U1 Triac

(Triode for AC)

Controls the full waveform of the

AC voltage

C1 56nF electrolytic capacitor

Reduces the amplitude and phase

delay of the AC waveformControls

the time triggering of the diac and

triac

TR1

Step-down Transformer

Current = 3A

Voltage Conversion =

220V to 50V

Down converts the AC voltage to a

maximum of 50V

J1 USB port Serves as the output terminal of

5V DC charger

Power Supply Specifications

AC OUTPUT DC OUTPUT CHARGER

Voltage Range 0 - 50V AC 0 - 50V DC 5V 0.5V DC

Maximum Current 3A 2A 500mA

Duration of Use

Per Day 6 hours 10 hours 1.5 hours

Per Session

hours

hours

hours

Charging Time

75% 6.3 hours 9.45V DC

50% 12.6 hours 6.3V DC

25%

(not recommended) 18.9 hours 3.15V DC

0%

(not recommended) 25.2 hours 0V DC

Chapter 6

Results and Discussion

This chapter summarizes and interprets all the data collected to assess

the performance of the system. The tests conducted include those for voltage

stability, voltage regulation and efficiency.

Voltage Stability

Voltage stability measures the output voltage deviation of the power

supply with respect to time of operation and with the changing of input.

INPUT VOLTAGE

(VDC)

TIME LAPSE

(MINUTES)

OUTPUT VOLTAGE

(VDC)

52.5 10 40.0

52.5 20 40.0

52.5 30 39.9

52.5 40 40.1

52.5 50 40.0

52.4 60 40.0

52.4 70 39.8

52.4 80 40.0

52.4 90 40.0

52.4 100 40.0

52.4 110 40.0

52.3 120 40.0

Table 6. Voltage Stability Results for DC Power Supply

Mean = (8)(40) + 39.9 + 40.1 + 39.8 + 40.2

12

Mean = 40

Variance = ( ) ( )

( )

Variance = 0.005

Standard Deviation = √

Standard Deviation = 0.171

The DC output of the power supply was set to operate continuously for a

maximum of two hours every laboratory class. In the table above, the expected

output should be 40V DC. By solving for the standard deviation, it was calculated

that the output voltage of the circuit only varies from the expected output by

0.171 volts.

Within two hours of using the DC supply, the rate of discharge of the

battery showed that it can maintain the expected output voltage continuously

within the set time of operation.

INPUT VOLTAGE (VDC)

TIME LAPSE (MINUTES)

OUTPUT VOLTAGE (VAC)

12.4 5 15.5

12.3 10 15.7

12.3 15 15.8

12.3 20 15.8

12.3 25 15.8

12.3 30 15.8

12.3 35 15.8

12.3 40 15.8

12.2 45 15.8

12.2 50 15.8

12.2 55 15.8

12.2 60 15.8

Mean = 15.5 + 15.7 + (10)(15.8)

12

Mean = 15.767

Variance = ( ) ( ) ( ) ( )

( )

Variance = 0.093

Standard Deviation = √

Standard Deviation = 0.305

Table 7. Voltage Stability Results for AC Power Supply

The AC output of the power supply was set to operate continuously for a

maximum of one hour every laboratory class. In the table above, the expected

output should be 15.8V AC. By solving for the standard deviation, it was

calculated that the output voltage of the circuit only varies from the expected

output by 0.305 volts.

Within one hour of using the AC supply, the discharge of the battery

showed that it can maintain the expected output voltage continuously within the

set time of operation.

Voltage Regulation

Voltage regulation is the measure of change in voltage magnitude

between the sending and receiving end of a component. Voltage regulation

describes the ability of the system to provide near constant voltage over a wide

range of load conditions. It is expressed as the ratio of the difference between

no-load and full-load output voltage of a device to the full load output voltage,

expressed as a percentage.

( )

NO LOAD OUTPUT

VOLTAGE (VDC) LOAD

OUTPUT VOLTAGE

WITH LOAD (VDC)

VOLTAGE

REGULATION

PERCENTAGE (%)

30 1050Ω 9.6 212

30 1100Ω 10.2 194

30 1150Ω 11.4 163

30 1200Ω 12.6 138

30 1250Ω 13.7 118

30 1300Ω 15.5 93

30 1350Ω 17 76

30 1400Ω 19.6 53

30 1450Ω 20.4 47

30 1500Ω 22.5 33

30 1550Ω 25.7 16

30 1600Ω 27.5 9

30 1650Ω 28.5 5

30 1700Ω 29.4 2

30 1750Ω 29.5 1

30 1800Ω 29.6 1

30 1850Ω 29.8 0.67

30 1900Ω 30 0

30 1950Ω 30 0

30 2000Ω 30 0

30 2050Ω 30.4 -1

30 2100Ω 31.2 -1

30 2150Ω 31.6 -1

30 2200Ω 32.3 -2

30 2250Ω 32.8 -4

30 2300Ω 33 -5

30 2350Ω 33.9 -5

Based from the result of the voltage regulation test done on the adjustable

DC voltage stage, the DC power supply can be effectively used for loads ranging

between 1500Ω to 2350Ω. This is because the output voltage on these loading

conditions was on the range of industry standard tolerance of 5% tolerance.

NO LOAD OUTPUT

VOLTAGE (VDC) LOAD

OUTPUT VOLTAGE

WITH LOAD (VAC)

VOLTAGE

REGULATION

PERCENTAGE (%)

5 1kΩ 3.3 51.52

5 1.5kΩ 3.3 51.52

5 2kΩ 3.5 42.86

5 2.5kΩ 3.7 35.14

5 3kΩ 3.7 35.14

5 3.5kΩ 3.7 35.14

5 4kΩ 4.2 19.05

5 4.5kΩ 4.2 19.05

Table 8. Voltage Regulation Results for DC Power Supply

5 5kΩ 4.5 11.11

5 5.5kΩ 4.7 6.38

5 6kΩ 4.8 4.17

5 6.5kΩ 4.8 4.17

5 7kΩ 4.9 2.04

5 7.5kΩ 5 0.00

5 8kΩ 5 0.00

5 8.5kΩ 5 0.00

5 9kΩ 5 0.00

5 9.5kΩ 5 0.00

5 10kΩ 5.1 -1.96

5 10.5kΩ 5.2 -3.85

5 11kΩ 5.2 -3.85

5 11.5kΩ 5.2 -3.85

5 12kΩ 5.3 -5.66

5 12.5kΩ 5.4 -7.41

Table 9. Voltage Regulation for AC Power supply

Based from the results of the voltage regulation test for the adjustable AC

stage, the AC power supply can be effectively used for the load between 4.5kΩ

to 10.5kΩ. This is because the output voltage on these loading conditions was

on the range of industry standard tolerance of 5% tolerance.

Efficiency

Efficiency is the measure of how much power at the input appears at the

output and therefore, less waste. Efficiency measurement for dc-dc power

supplies is carried out in a similar fashion as ac-dc power supplies. In the case of

DC - DC power supplies, there will be no specifications for power factor, total

harmonic distortion and frequency. There are no changes in the loading

calculations for dc-dc power supplies. The formula for efficiency is the ratio of

output power to the input power.

∑

Where

η = Efficiency (%)

Po, i = Ouput power of the ith output

Pin = Input power

To test the efficiency for both DC and AC power supply, the power input

and output at 50% load regulation was used. For DC, the output voltage varies

from 30V to 19.6V with a resistance of 1400Ω and has an output power of

0.27W. For AC, the output voltage varies from 5.3V to 3.3V with a resistance of

1000 to 1500 ohms and has an output power of 0.01W.

DC SUPPLY EFFICIENCY AC SUPPLY EFFICIENCY

By getting the average efficiency of the DC and AC supply, the overall

system efficiency was 92.79%.

Chapter 7

Conclusion and Recommendation

Solar Powered AC/DC Power Supply for Electronics Engineering was a

solar independent stand-alone power supply for laboratory excercises of

Electronics Engineering students. The power supply was designed in accordance

to the power requirements in the laboratory of Bataan Peninsula State University,

College of Engineering and Architecture, Department of Electronics Engineering.

The power supply was divided into three main stages: the solar charger stage

composed of a boost converter, adjustable AC stage (0 to 50V AC) regulated by

a DIAC and TRIAC phase control with a step – down transformer and adjustable

DC (0.7 to 50V DC) composed of linear series voltage converter. The AC can be

used for six (6) hours per day, the DC can for ten (10) hours per day, and the

charger for one and a half hours (1½ ) per day. The AC and DC output of the

power supply was not intended for simultaneous operation.

The following were the recommendations based from the testing and

results gathered by the proponents:

1. Minimize the number of batteries and switches used in this design that

can be done using a switch mode buck-boost converter with its greater

efficiency advantage but consider the ripple and noise implications

2. Digital display for the output terminal of AC and DC voltages battery state

and conditions to enhance the safety and accuracy of the power supply

3. Use a voltage buffer and attenuator before the output stages to isolate

each stage to the load to improve its load regulation and line regulation to

avoid the loading effects.

4. Improve the interface of power supply to the user making it for easier to

the students to use.

6. Increase the system efficiency.

7. Improve the voltage stability.

8. Developed the system so that AC and DC and charger can be used

simultaneously.

References

Mohan, Undeland and Robbins, Wiley. (1989) Power Electronics: Converters,

Applications and Design.

B. M Hasaneen and Adel A. Elbaset Mohammed. (2008, December) Design and

Simulation of DC/DC Boost Converter.

Wens, M. Steyaert, M. (2011) DC - DC converter.

Dallas Semiconductor. (2000, October 19) DC-DC Converter Tutorial - MAXIM

power supply circuits.

Muhammad H. Rashid. (2001) Power Electronics Handbook. University of West

Florida

Boylestad, Robert l. and Nashelsky, Louis. (2009) Electronic Devices and Circuit

Theory, 10th Edition

Solar Energy. (2015, February 9)

Available: http://en.wikipedia.org/wiki/Solar_energy

(March 10, 2015)

Photovoltaics.

Available: http://en.wikipedia.org/wiki/Photovoltaics

(March 10, 2015)

Solar Charger.

Available: http://en.wikipedia.org/wiki/Solar_charger

March 10, 2015

Types of Renewable Energy.

Available: http://www.renewableenergyworld.com/rea/tech/home

(Match 10, 2015)

Why is renewable energy important?

Available: http://www.renewableenergyworld.com/rea/tech/why

(March 10, 2015)

Power Reliability

Available: http://www.westernpower.com.au/customer-service-power-

reliability-and-quality.html

(March 10, 2015)

Solar Power.

Available: http://www.westernpower.com.au/customer-service-power-

reliability-and-quality.html

(March 11, 2015)

Hnin Mar Wai and Zaw Min Min Htun. Design and Construction of Variable DC

Source for Laboratory Using Solar Energy.

Available: www.ijecse.org

(March 11, 2015)

Uses of Solar Energy.

Available: http://www.solarbuzz.com/going-solar/using/uses

(March 2015)

Why Solar?

Available:http://www.engineering.com/SustainableEngineering/Renewable

EnergyEngineering/SolarEnergyEngineering/WhySolarEnergy/tabid/3893/

Default.aspx

(March 2015)