Vishal THESIS

PERFORMANCE CHARACTERIZATION OF CHARGE
CONTROLLERS: AN EXPERIMENTAL COMPARISON WITH
APPLICATION TO DEVELOPING NATIONS
BY
VISHAL CHANDRASHEKAR
B.E. P.E.S COLLEGE OF ENGINEERING (2013)
SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF MASTER OF SCIENCE
DEPARTMENT OF MECHANICAL ENGINEERING
UNIVERSITY OF MASSACHUSETTS LOWELL
Signature of
Author: Date:
Signature of Thesis Supervisor:
Name Typed: Prof. Christopher Niezrecki
Co-supervisor:
Name Typed: Alessandro Sabato, PhD
Signature of other Thesis Committee Members:
Committee Member Signature:
Name Typed: Asst. Prof. Ertan Agar
Committee Member Signature:
Name Typed: Prof. Walter Thomas

PERFORMANCE CHARACTERIZATION OF CHARGE
CONTROLLERS: AN EXPERIMENTAL COMPARISON WITH
APPLICATION TO DEVELOPING NATIONS
BY
VISHAL CHANDRASHEKAR
ABSTARCT OF A THESIS SUBMITTED TO THE FACULTY OF THE
DEPARTMENT OF MECHANICAL ENGINEERING
IN PARTIAL FULLFILMENT OF THE REQUIREMENTS
FOR THE DEGREE OF
MASTER OF SCIENCE
IN
ENERGY ENGINEERING
UNIVERSITY OF MASSACHUSETTS LOWELL
2016
Thesis Supervisor: Christopher Niezrecki, PhD.
Chair, Professor, Department of Mechanical Engineering
University of Massachusetts Lowell
Thesis Co-Supervisor: Alessandro Sabato, PhD.
Postdoctoral Research Associate, SDASL, Department of Mechanical Engineering
University of Massachusetts Lowell

ii
ABSTRACT
Charge controllers (CCs) are essential devices for managing power between the solar
module, battery and the load in a SHLS (Solar Home Lighting System) unit. CCs
influence battery life, load compatibility, overall system efficiency and importantly,
system life cycle cost. A wide range of CC devices are available with varying degrees of
performance, protective measures and retail prices. It was decided to characterize and
analyze performance of 5 devices which broadly represent the different gamut of
products commercially available.
This work performs a comparison of different CC devices through experimental testing,
validation of data provided by the manufacturers, and estimating the suitability of a
particular charge controller for application in SHLS units by understanding device
behavior. A deep-cycle lead acid battery was discharged and charged using each of the
CCs and the voltages and currents to and from the modules, load, and battery were
sampled every 30 seconds during testing. Charging Discharging Cycle Profiles (CDCPs)
for the 5 devices were obtained for analysis. Two iterations of CDCPs were created; one
with and without a simultaneous cell-phone battery equivalent load. This was done to
simulate the charging of a cell-phone during the day and night time. A simulation for
calculating overall lifecycle cost of the system was also created.

iii
It was observed that the CDCPs without loading for two different specimen of the same
brand showed some variability in performance. The battery discharging times were varied
as well. Adherence to the set-points was found to be moderately close to the stated values
in the manufacturer specified data sheet. However, the two specimens showed slightly
different set-points which demonstrate a slight lack of reliability. The power consumed
by most of the devices was higher compared to the manufacturer specifications.
Life Cycle Cost (LCC) analysis using a theoretical cycle as standard revealed that the
overall cost of operation of a CC including its own cost varies by about $100 depending
on the device. The errors between the theoretical performance and the measured
performance did not exceed 3% for most of the devices.

iv
DEDICATION
This night is dark, the waves rise mountain high.
And a storm is raging!
What do the pedestrians know my plight moving
Upon the shore that’s safe and dry?
Hafiz
For the millions, who have been living and continue to live without lights: I hope this
work and the toil of those involved will create at least an iota of change.
To my parents: Arun and Lalitha, thanks for having faith in me. It is one of the things that
kept me going. I do not know what makes you think that I am capable of accomplishing
my dreams but I shall do my best. To my sister Sumukhi: you inspire me in ways that I
have not yet understood. Krish: I seek to duplicate your equanimity one day especially in
profession. Nishaan, few people believe in me like you do. “Miles and miles to go before
we sleep”. To Mahathi: you may want to read this when you grow up. To Cooby, my
eternal courage replenishment mechanism: I revel in your company even in your absence.
A special thanks to all of my family who have contributed to whatever I am today.
This work is dedicated to among others, my dearest friends Mohsin, Yao, Abiola, Gargee,
Anisha, Vyas, Vikas, Shashank, Kishan, Gautam, Mathews, Phaneendra, Ravi, Shyam,
and Arpitha: yes, I am still late at everything I do.
This has been a journey more spirited and unexpected than what I had imagined. I have
learnt a lot more than what have filled these pages.
Thank you.

v
ACKNOWLEDGEMENTS
I thank Prof. Niezrecki for his continued guidance, support and belief that I would come
up with something significant after two years. Thank you for your support and
encouragement. It was due to your vision that I was able to work on an important and
interesting topic.
I would like to thank all the committee members Prof. Thomas and Prof. Agar for their
constructive comments to add more substance to this work.
Sincere thanks to Alessandro for guiding me through the process writing this manuscript.
Thanks to Glen Bousquet and Don Bowden for troubleshooting as well educating me on
electronics and supplying me with necessary electrical components. Thanks to Jackie
Paradise for helping me with numerous issues.
Thank you all.

vi
TABLE OFCONTENTS
ABSTRACT....................................................................................................................... ii
DEDICATION.................................................................................................................. iv
ACKNOWLEDGEMENTS ............................................................................................. v
TABLE OF CONTENTS ................................................................................................ vi
LIST OF FIGURES .......................................................................................................viii
LIST OF TABLES........................................................................................................... xi
I. INTRODUCTION ..................................................................................................... 1
1.1 Motivation.........................................................................................................................1
1.2 Energy access: problem and potential solution............................................................2
1.3 Review of current solar devices enabling energy access ............................................6
1.4 Review of related literature...........................................................................................11
II. THEORY OF CHARGE CONTROLLERS AND BATTERIES ....................... 15
2.1 Overview .........................................................................................................................15
2.2 Classification and configuration of charge controllers .............................................17
2.2.1 Charge controllers based on shut off regulation ......................................... 18
2.2.2 Maximum Power Point Tracking (MPPT) and Pulse Width Modulation
(PWM) Circuits........................................................................................... 26
2.3 Voltage set points...........................................................................................................29
2.4 Battery fundamentals.....................................................................................................33
2.5 Charging-discharging cycle plots.................................................................................36
2.6 Observed issues ..............................................................................................................39

vii
III. METHODOLOGY.................................................................................................. 40
3.1 Overview .........................................................................................................................40
3.2 Equipment used and experimental setup.....................................................................41
3.2.1 Lighting and current sources....................................................................... 43
3.2.2 Current and Voltage measurements............................................................ 45
3.2.3 Battery properties........................................................................................ 47
3.2.4 Charge controllers....................................................................................... 47
3.2.5 Loads .....................................................................................................................51
3.3 Experiment 1: Setup of the CDCP experiment with no CBE...................................53
3.4 Experiment 2: Setup of the CDCP for the simultaneous loading case....................55
3.5 Theoretical model to estimate lifecycle cost ..............................................................61
IV. RESULTS AND DISCUSSIONS............................................................................ 63
4.1 Overview .........................................................................................................................63
4.2 Results: EXP. 1...............................................................................................................65
4.3 Results: EXP. 2...............................................................................................................75
4.4 Calculation of LCC using theoretical battery model.................................................82
V. CONCLUSION AND FUTURE WORK............................................................... 88
VI. REFERENCES ........................................................................................................ 92
APPENDIX.................................................................................................................... 100
APPENDIX. 1........................................................................................................................100
APPENDIX. 2........................................................................................................................106
APPENDIX. 3........................................................................................................................109

viii
LIST OFFIGURES
Fig. 1.1 Access to electricity (in percentage) of population in developing countries
(Source: [4])....................................................................................................................... 3
Fig. 1.2 Modeled annual average radiation (Source: [11]) ................................................ 6
Fig. 2.1 Different kinds of PV systems ............................................................................ 15
Fig. 2.2 Different types of CC based on cycling .............................................................. 17
Fig.2.4 Block diagram representing the circuit schematic of a shunt type [39] .............. 20
Fig. 2.5 Current variation (top) and voltage variation (bottom) in a system operated using
a shunt type Interrupting Charging CC [41] .................................................................... 21
Fig. 2.6 Circuit representation of Series type CC [39] .................................................... 23
Fig. 2.7 Current variation (left) and voltage variation (right) in a system operated using a
series type Interrupting Charging CC [41]....................................................................... 24
Fig. 2.8 Theoretical I-V curve of a solar module [43] ..................................................... 27
Fig. 2.9 Schematic of a generic PWM CC [42] ............................................................... 27
Fig. 2.10 Schematic of a generic MPPT CC [42] ............................................................ 28
Fig. 2.11 Illustration of hysteresis in the regulation and disconnection regions of a typical
charge-discharge cycle [39] ............................................................................................. 32
Fig. 2.12 3-stage theoretical charge cycle [48] (left) and CDCP of a 12V LA battery [49]
(right) ............................................................................................................................... 36

ix
Fig. 3.1 Werker battery charger used to replenish the battery before starting each
experiment [50] ................................................................................................................ 42
Fig. 3.2 30W solar module selected [52] ......................................................................... 43
Fig. 3.3 Arrilite 1000W lamp ........................................................................................... 43
Fig. 3.4 CR5210-5 DC current transducer [53] ............................................................... 45
Fig. 3.5 Performance curve of the CR2510-5 transducer ................................................ 46
Fig. 3.6 NI USB-6001 DAQ device [54] (left) and NI LabView block diagram for data-
acquisition (right) ............................................................................................................. 46
Fig. 3.8 LED Strips used as load ...................................................................................... 51
Fig. 3.9 Portable battery pack used as cellphone battery equivalent [67] ........................ 52
Fig. 3.10 A step down buck used to charge the power bank [68] .................................... 52
Fig. 3.11 CBE discharging power resistor [69] ............................................................... 53
Fig. 3.12 Schematic of the discharging cycle .................................................................. 54
Fig. 3.13 Schematic of the charging cycle ....................................................................... 54
Fig. 3.14 CDCP with contemporary loading ................................................................... 56
Fig. 3.15 Entire experimental setup (1) PV module, 5) Digital multimeter) ................... 57
Fig. 3.16 Detail of the experimental setup (2) Current to Voltage Transducers, 3) DAQ,
4) Voltage dividers on breadboard, 6) LA Battery, 7) CC, 8) LED strip, 9) CBE, 10) Step
down buck)....................................................................................................................... 57
Fig. 3.17 Dynamic battery model utilized (source: [70]) ................................................. 61
Fig. 4.1 CDCP of the currents for the ten devices for EXP.1 .......................................... 67

x
Fig. 4.2 CDCP of the voltages for the ten devices for EXP.1 .......................................... 68
Fig. 4.3 CDCP of the power for the ten devices for EXP.1 ............................................. 69
Fig. 4.4 CDCP of the currents for the five devices for EXP.2 ......................................... 78
Fig. 4.5 CDCP of the voltages for the five devices for EXP.2 ........................................ 79
Fig. 4.6 CDCP of the powers for the five devices for EXP.2 .......................................... 80
Fig. 4.7 Theoretical CDCP for the LA AGM battery ...................................................... 85
A 1.1 CDCP of CMO1 (EXP. 1) .................................................................................... 100
A 1.2 CDCP of CMO2 (EXP. 1) .................................................................................... 101
A 1.3 CDCP of CTO1 (EXP. 1) ..................................................................................... 101
A 1.4 CDCP of CTO2 (EXP. 1) ..................................................................................... 102
A 1.5 CDCP of STO1 (EXP. 1) ..................................................................................... 102
A 1.6 CDCP of STO2 (EXP. 1) ..................................................................................... 103
A 1.7 CDCP of MS01 (EXP. 1) ..................................................................................... 103
A 1.8 CDCP of MS02 (EXP. 1) ..................................................................................... 104
A 1.9 CDCP of WN01 (EXP. 1) .................................................................................... 104
A 1.10 CDCP of WN02 (EXP. 1) .................................................................................. 105
A 2.1 CDCP of CM03 (EXP. 2) .................................................................................... 106
A 2.2 CDCP of CT01 (EXP. 2) ...................................................................................... 106
A 2.3 CDCP of ST01 (EXP. 2) ...................................................................................... 107
A 2.4 CDCP of MS01 (EXP. 2) ..................................................................................... 107
A 2.5 CDCP of WN03 (EXP. 2) .................................................................................... 108

xi
LIST OFTABLES
Table.1.1 Percentage population having access to electricity (Source: [5]) .......................... 4
Table 1.2 List of units and metrics used ................................................................................ 8
Table 1.3 Comparison of the SLS devices ............................................................................. 9
Table 1.4 Comparison of commercially available SHLS kits ............................................. 10
Table 2.1Comparison of the different features of PWM and MPPT CCs ........................... 29
Table 2.2 Definition of the commonly used set-points ........................................................ 31
Table 2.3 Typical Set points for a Lead Acid battery [39] .................................................. 32
Table 3.1 Figures of the Charge Controllers being used ..................................................... 49
Table 3.2 Specifications of the different CCs tested ........................................................... 50
Table 3.3 List of components used ...................................................................................... 59
Table. 3.4 Test matrix .......................................................................................................... 60
Table 4.1 Comparison of the features for the different CCs for EXP. 1 ............................. 74
Table 4.2 comparison of the features for the different CCs for EXP. 2 .............................. 81
Table 4.3 LCC calculation for the different devices ............................................................ 83
Table 4.4 Relation between DoD and life cycle till failure [73] ......................................... 86

1
I. INTRODUCTION
1.1 Motivation
Solar Photo-Voltaic (PV) modules are becoming more affordable and utilize the abundant
solar resource to generate electricity. This makes them suitable for being used in areas
characterized by lack or intermittent supply of electricity from the grid. Moreover, off-
grid LED lighting systems are cleaner, cheaper and healthier than kerosene lamps being
used today [1, 2]. PV modules alone cannot generate electricity; auxiliary components
such as batteries for energy storage and electronic control units are required to allow
users to connect their load and use the energy. Electronic control units such as charge
controllers (CCs) play a key role in the whole system as they direct energy from the
modules to the battery and loads. The purpose of this work is to compare and evaluate the
performance of different solar CC devices. The obtained results may be used to help
develop a PV system that can be operated inexpensively and used for lower-income
regions in third-world countries.
Small PV systems (less than 100W) comprising of PV modules, CC, wiring, batteries,
and lights bundled together are often referred to as Solar Home Lighting Systems
(SHLSs). Most existing SHLSs simply integrate components ordered from different
suppliers. Furthermore, most of these devices are imported; hence, do not encourage local

2
enterprise and also lack the desired robustness. Since the commercially available systems
usually embed the electronic components, they are not modular or expandable and are
very difficult to repair by end users.
A critical part of a SHLS is the charge controller (CC) and there is a need to better
understand the performance of the variety of CCs currently available on the market today.
This study consists of an experimental and theoretical analysis to better understand the
behavior of different market-available CCs and quantify their performance. To do this,
elaborate experiments were created and the Charge-Discharge Profiles (CDPs) for
different loaded and unloaded conditions were obtained and compared.
The thesis work is organized as follows: after chapter one where the problem of energy
access is discussed together with a short survey of the scientific literature addressing this
problem, some basic concepts concerning CCs, charging cycles and batteries are
discussed in chapter two. In chapter three, a detailed description of the experimental
setup and procedure are laid out. Chapter four comprises a detailed analysis of the
obtained results. To finish, the knowledge gained from this work is summarized and a
description of possible future work addressed in chapter five.
1.2 Energy access: problem and potential solution
According to the United Nations Secretary General’s Advisory group on Energy and
Climate Change, energy security is defined as “uninterrupted access to clean, reliable
and affordable energy services for cooking and heating, lighting, communications and
productive uses at an affordable and environmentally friendly price” [3]. Energy is vital

3
for survival regardless of the lifestyle. With reference to developing nations, several
studies have been performed by the World Bank (WB) which have shown that access to
electricity in many areas of the world is extremely limited. Figure 1.1 depicts the
percentage of people having access to electricity. From a preliminary analysis of the
image, it is observed that a lack of energy access characterizes developing nations and
areas such as the Sub-Saharan Africa, where access to electricity is very low and below
23%, or the Indian subcontinent where less than one out of two people have access to
electricity.
Fig. 1.1 Access to electricity (in percentage) of population in developing countries (Source: [4])
Furthermore, the grid does not connect to a large percentage of the population, especially
those living in rural areas as summarized in Table.1.1.

4
Table.1.1 Percentage population having access to electricity (Source: [5])
Region
People without
power
(millions)
Access to
electricity
(%)
Urban
electrification
rate
(%)
Rural
electrification
rate
(%)
Sub-Saharan
Africa
599 31 55.2 18.3
Malawi 14 7 37 1
Gabon 1 60 64 34
Democratic
Republic of Congo
62 9 26 1
Developing Asia1
615 83.1 95 74.9
India 306 75 94 67
Myanmar 25 49 89 29
Pakistan 56 69 88 57
Cambodia 9 34 97 18
Yemen 14.9 40 75 23
Latin America
Haiti 7.3 28 44 9
Peru 3 90 98 60
Nicaragua 1.3 78 98 50
For instance, it should be pointed out that India, despite an access rate to electricity equal
to 75%, has the higher number of people (306 millions) not connected to the grid. It is
due to the enormous population and to the disparity in energy access between
communities living in urban areas (94%) compared to rural areas (67%). The grid does
not reliably supply rural regions for they are sparsely populated and requires massive
investment to connect each and every village to the grid. This difference is even more
evident in the cases of regions like the Sub-Saharan ones are considered (e.g. Malawi).
Moreover, even if the grid connection exists, supplied power typically exists only for a
few hours each day and it is prone to outages. Also, transmission of electricity is another
issue for providing a reliable source of energy as it typically encompasses huge losses
1
Developing Asia includes China, India, Cambodia, Indonesia, Laos, Malaysia, Myanmar, Philippines,
Singapore, Thailand, Bangladesh, DPR Korea, Mongolia, Nepal, Pakistan, Sri Lanka

5
(usually from 11% - 54% including pilferage [6]) from the power plant to the consumer.
Theft of energy is also a major issue. On the other hand, population is growing especially
in those regions where access to electricity is low [7], simultaneously increasing the
demand for conventional energy supplies and at the same time there is need keep the cost
of electricity affordable [8].
On the other hand, conventional sources of energy are depleting at an alarming rate,
which makes the access to low-cost energy even more difficult. The exponential growth
in fuel consumption is now driven by shale discoveries and natural gas [9] especially in
the developed countries, which is yet more polluting compared to solar energy. As the
population increases, demand for oil increases too and CO2 emissions are estimated to
grow, leading to catastrophic consequences attributed to climate change [10].
As can be seen from Figure 1.1 and 1.2 – the countries lacking energy access are
typically the ones that have access to the solar energy resource. The regions where
unavailability of electricity is abundant are also the regions where the potential for power
generation using Solar Lighting Systems (SLS) are higher. In particular, Sub-Saharan,
developing Asia, and Latin America areas characterized by a scarcity of electricity access
are characterized by an annual average solar irradiation between 5.5 and 7.5kWhm-2
[11].

6
Fig. 1.2 Modeled annual average radiation (Source: [11])
Solar energy has the ability to partially supply the needs of the planet. The resource is
distributed and makes it easy to produce energy at the site of consumption. The
possibility of generating electricity where needed could help the business by creating new
customers, provide affordable lighting to people having no access to the grid, and prevent
much damage to the environment. By implementing SHLS and PV systems with battery
storage, it may be possible for people or communities to become independent of grid-tied
electricity.
1.3 Review of current solar devices enabling energy access
A simple solution currently employed to provide to access to lighting for the masses has
been the deployment of Solar Lighting Systems (SLS). These devices are palm sized and
usually have an embedded PV module to recharge a Lithium battery. The SLS may or
may not offer ability to charge a cellphone. The purpose of SLSs is to provide some

7
illumination mainly for task lighting during cooking, studying, cleaning etc. SLSs are
also compact and can be carried around to illuminate walking paths during night travel.
The SHLSs cater to slightly higher capacities and are usually stationary. These are
heavier, capable for larger loads and more loads can also be added. For instance, two or
more USB ports may be available in addition to LED bulbs which can be placed at
different points in the house to illuminate different areas simultaneously. SHLS devices
can either be sold as a kit or the user/ distributor/ installer may bundle together various
components of assorted manufacturers.
This section presents few of the popular devices in tabular form. Table 1.2 presents the
different parameters that shall be compared among different devices. Table 1.3 compares
different parameters of SLS devices. Table 1.4 compares different SHSL devices that are
sold as a kit.
These comparisons try to elaborate on the different devices available in the market in the
respective market segments. However, this thesis concerns the analysis of CC devices
that are not part of a kit and these devices form a part of bundled SHLS systems. The
devices in the Table 1.4 have larger capacity modules, more number of LED bulbs than
those devices in Table 1.3.

8
Table 1.2 List of units and metrics used
Measurement Unit Explanation
Luminous flux Lumen (lm)
Brightness of the luminary or LED bulb. Higher
the brightness of the bulb higher would be the
ease of sight in the region of illumination.
Battery capacity mAh
This is the amount of energy stored in the battery.
Higher the battery capacity means that the device
would be functional even during cloudy days or
when irradiance is low.
Unit cost of
luminance
lm/$
This unit needs to be as low as possible in order
to maximize the customer’s willingness to buy.
Luminous efficacy lm/W
This is a measure of how the efficient the LED
bulbs which are used in the device are. Ideal is to
provide highest illumination whilst consuming
lowest battery power. These are calculated for
highest settings.
.

9
Table 1.3 Comparison of the SLS devices
Product Company Lumens PV panels Battery
Cost
in $
Hours of
operation
on full
charge
Cost of
system
Lumen/
$
Luminous
efficacy
Lumen/watt
SunKing Solo
Greenlight
Planet
51
800 mW and
4.7 V
1000 mAh
3.2 V
Lithium
Ferro
Phosphate
24.94
[13]
5.8 hours in
Highest
setting
2.04 130 [14]
MiniSun 12H
SunLife NA
200 mW Poly
crystalline
[15]
NA 6 [15] 12 [15] NA NA
S20
dlight design 29 [16]
Mono
crystalline
silicon
0.4 W
[16]
Lithium
battery
10.31
[17]
6.5 2.81 NA

10
Table 1.4 Comparison of commercially available SHLS kits
Product Company Lumens PV panels Battery
Cost
in $
Hours of
operation
on full
charge
Cost of
system
Lumen/
$
Other
Features
S300
dlightdesign
100/ 29
[18]
1.6 W Mono
Crystalline
silicon
1800 mAh
Lithium
Iron
Phosphate
38.34
[19]
High 5 hours
and low 26
hours
2.86
1 USB
charging port
Connect 600
Barefoot
Power
300 (4 lamps)
[20]
6.6 W
Poly
Crystalline
silicon
[20]
Sealed
Lead Acid
[20]
NA
11 hours
with 4 lamps
[20]
NA
2 USB
charging
ports + 1 x
12V DC port
[20]
Energy Station Plus
Futura 320 [21] 4.7 W [21]
4400 mAh
6.4 V
Lithium
[21]
NA
6.4 hours
with 3 lamps
[21]
NA
1 USB
charging port
[21]

11
1.4 Review of related literature
Much research has been done on the comparison, innovation, field testing, and economic
analysis of utility-scale Solar Lighting Systems (SLSs) or home lighting systems for
developed countries. This thesis hereby presented is an extension of these works but it
focuses on those CCs which are an integral part of Solar Home Lighting Systems
(SHLSs) which serve a slightly higher load. Some of the works focusing mainly on CCs
and stand-alone PV systems have been presented in this section to provide a preliminary
survey of the state-of-the-art of this technology.
One of the internationally accepted standards for performance of the charge controllers
are given by the International Electrochemical Commission (IEC) [22]. The IEC 62509:
2010 is currently being followed as far as battery CCs for PV systems. However, it is
interesting to note that none of the CCs purchased for this study did not mention
compliance to the IEC 62509 code.
During the 1990s, there were some standards that were used to determine the adequate
performance of CC devices. Some countries had set standards for CCs and implemented
them in their respected jurisdictional areas, for example: Basic Electrification for Rural
Households prescribed by GTZ in Germany and the Specifications for Solar Home
Systems prescribed by BPP Technologies in Indonesia. But none of the standards had a
truly global reach. Though PV modules’ performance is regulated stringently, the same
cannot be said for other solar system components such as lightening and controllers.
Egido et al. [23] analyzed the standards of different countries in 1998. In 2005 and 2010,
the International Electro-technical Commission (IEC) released two technical standards

12
for charge controllers regulation: the IEC 62093 (Balance-of-system components for
photovoltaic systems - Design qualification natural environments) and the IEC 62509
(Battery charge controllers for photovoltaic systems - Performance and functioning). The
parameters discussed in the standards were devised keeping in mind both the national
governments that intend to implement SHS and also to the CC manufacturers, who can
manufacture better and longer lasting devices. The final benefit goes to the consumer
who purchases a SHS devise. This work is a review of the Universal standard prescribed
by the European Commission [24].
Charge controllers have been tested and validated before: Diaz et al. [25] compared the
different batteries and charge regulators for application in Solar Home Lighting Systems
(SHLSs). This work was essentially the verification of above discussed proposed
Universal Technical Standards. A result of this study showed that though the cost of a
charge regulator was about 5% of the whole system’s cost, improper charging cycles due
to flawed regulators can lead to severe reductions in the life of the battery and therefore
increasing lifecycle costs. 20 charge regulators were tested in the research, out of which 3
failed completely. It was observed that the performance of these devices were unreliable,
varying and not well adapted to the batteries that was used for testing. The study
presented in this thesis is similar to the one performed by Diaz, with the difference that
the CDPs were also obtained for CCs of different price ranges. In particular, CDPs with
and without load have also been presented to gain a better understanding of the CC
behavior under different operational conditions. Also, the analysis presented in this thesis
was performed on more modern devices together with an estimation of lifecycle cost.
These features are not studied in the mentioned study, even if it should be noticed that

13
some of the critical performance characteristics pointed out by Diaz’s research were
confirmed by the experimental results presented in the thesis.
Different types of CCs, batteries and recommended practices have been elaborated in
Usher et al. [26] and Dunlop et al. [27]. In these studies, the schematics, mode of
operations, behavior, battery maintenance, and suitable applications for the considered
CCs have been analyzed and discussed with great detailed.
In large areas of Africa and other developing countries, deep-cycle batteries suited for
SHLSs applications are not easily available and quite expensive compared to abundant
automobile batteries. In general, the CCs are not compatible with automobile batteries as
their interaction can cause premature system failures. Masheleni et al. [28] developed an
idea to use microprocessors (SGS-Thompson microcontrollers, ST62E20) as CCs to try
to emulate the theoretical battery cycle for deep charging Lead Acid (LA) battery
applications. This study showed that the microprocessor could be easily programmed to
suit the requirements of an automobile if connected to the system, thus significantly
extending the battery life. Other advantages resulting from using microprocessors
included in-built system monitoring aides, reduced power consumption, elimination of
analog feedback, and simple modification of the circuit.
Few studies have been found which discuss the economics, feasibility, and Life Cycle
Cost (LCC) of small PV and wind systems. Nafeh [29] and Chel et al. [30] presented
models to analyze economics of the systems. In the latter study, using the electrical load
and daily average insolation on a tilted surface, capital cost and unit cost of electricity
were evaluated using LCC methods.

14
Some important technical papers were discussed above; now some outcomes of research
activities undertaken by respective institutions are presented. D-Labs at the
Massachusetts Institute of Technology (MIT) has been assessing the field performance of
SLS in various test sites in Africa and Central America [31]. A database of locally
available devices was created and sorted based on cost, performance, durability, lighting
output etc. [32].
The Lumina project [33] has published numerous studies on the performance analyses,
testing procedures, acceptability of products to the consumer, comparison of SLSs
against kerosene lamps, and adoption of SLSs into various other useful applications. An
important phenomenon of “market spoiling” concerning proliferation of LED lighting
devices was introduced by this group – this refers to “consumer skepticism” brought
about toward solar and LED lighting devices due to the consumers’ unsatisfactory first
experiences with these devices owing mainly to their lack of reliability and shorter than
advertised life. Rigorous testing and validation to help prevent “market spoiling” in the
realm of CCs in among of the aims of this work.
Lighting Global is an institution born out of the collaboration between the World Bank
and the Internal Finance Corporation (IFC). The goal of Lighting Global is to maintain a
quality standard for Solar Home Lighting System (SHLS) “that set a baseline level of
quality, durability, and truth-in-advertising to protect consumers”. Lighting Global tries
to make its standards and testing procedures having establishing laboratories or affiliated
testing facilities administered by regional organizations – Lighting Africa, Lighting Asia
and Lighting Pacific [34]. Lately, Lighting Global has established standards for ‘Solar
Home System Kits’ which are slightly larger capacity lighting devices [35].

15
II. THEORYOFCHARGE CONTROLLERSAND BATTERIES
2.1 Overview
SHLSs are widely adopted in regions where the access to a reliable grid is limited,
expensive, or nonexistent. Decrease in the solar modules and electronics’ cost have
propelled their growth and the trend is continuing in the near future [36].
Solar systems are classified based on their dependency on the grid into Stand Alone
Systems (SAS) and Hybrid systems as shown in Figure 2.1.
Fig. 2.1 Different kinds of PV systems
SAS systems are characterized by the absence of interaction with the grid, while the
hybrid systems by the presence of a photovoltaic system with another power generating
Hybrid PV
CLASSIFICATION BASED ON
GRID DEPENDANCY
Stand Alone PV
DC Loads AC
Loads
DC/ AC
Loads

16
energy source (e.g. wind, diesel engine). The schematic of a SAS is extremely simple and
includes, beside the presence of PV panels, a Charge Controller (CC), a battery bank, and
a load. Charge Controllers are basically DC-to-DC converters, which manage the power
output from the modules to the battery and from the battery to the loads. Several CCs
exist and the use of one type rather than another depends on the tasks being performed.
Loads can be of three different types (i.e. Direct Current (DC), Alternating Current (AC),
and DC/AC) and define the system further. It should be noticed that this study focuses on
the description of the DC loads SASs only, because their simplicity best fits the
necessities of remote and impoverished areas. Indeed, any AC conversion needs
accessory systems such inverters, which increase system’s complexity and cost [37].
In this chapter, a brief overview and characterization of the different CCs and their
respective circuit diagrams’ schematics are provided. This includes a discussion about the
relevance of the CC set-points to better understand the performed analyses. Then an
introduction about battery design is given, including an explanation of the theoretical
charging cycle. To finish, some generic issues CC devices experience during their
operations are described.

17
2.2 Classification and configuration of charge controllers
Generally, SHLSs have capacities within 100 W as they are mainly used for supplying
individual home lighting or small appliances only. Due to their characteristics, all the
energy needed by the system has to be generated and stored at any time on site.
Therefore, battery depletion or lack of sunlight must be taken into account before
designing a stand-alone system.
The features of the systems’ different components such as battery requirements and CC
characteristic depend on the applications the system is being designed for. For instance, if
the system is idle for a prolonged duration, the CC needs to top-up the depleted charge to
prevent battery failures under times of need. On the other hand, when the cycling rates
are higher, the CC needs to supply higher voltages for a certain time to break up the
Sulphation as will be specified in paragraph 2.4 [38]. Figure 2.2 shows a classification
based on the particular application CCs are used for.
Fig. 2.2 Different types of CC based on cycling
CLASSIFICATION BASED ON APPLICATION
Topping
Charge
Cycling Charge
Shallow Cycling Deep Cycling

18
As a small portion of the energy stored within the battery is used (e.g. during emergency
or black-out), the topping charge provide immediate replenishment of the used power by
means of the charger controller which allows the battery to be ready in the event of other
emergencies. In this situation, only a short percentage of the power stored within the
battery is used, and only a small amount has to be replenished. The system is idle for all
the other time. Such systems may be used in telephone towers and medicine storage
rooms where the shortest power outage cannot be tolerated. In cycling charge conditions,
the battery needs to be replenished many more times than topping charge since many
discharge and charge cycles occur. Two different kinds of cycling conditions can exist:
shallow and deep. In the former, the battery is partially discharged before being
recharged; while in the latter, the battery is fully discharged and then recharged. In deep
cycling charge conditions, the battery needs to be designed to accommodate a greater
Depth of Discharge (DoD) and the CCs need to recharge the batteries quicker.
2.2.1 Charge controllers based on shut off regulation
Another way to classify the CCs is based on the shut off voltage and voltage regualtion
mechanism as shown in Figure 2.3.

19
Fig.2.3 CC classification based on shut off and voltage regulation [39]
Based on the shut off mechanism, CCs are divided into Shunt type and Series type. In
Shunt type CCs the energy from the array is shut off as soon as a pre-determined voltage
is reached by shunting the circuit. This mechanism is quite simple, relatively inexpensive,
and it is generally used for systems having voltages lower than 24V [39].
As shown in Figure 2.4, where the block diagram of a shunt type circuit is shown, the
“control” switch is in parallel to the PV module. This means that when the control is
switched on (i.e. closed circuit), the power generated by the module is sent back and
cannot reach the rest of the system. It allows to maintain a constant voltage charging
cycle. No harm is caused to the PV modules by short circuiting them, since the PV
modules are basically current sources [40]. Also, the presence of a diode prevents the
battery from short-circuiting when the PV module is disconnected [40]. LVD is the Low
Voltage Disconnect which prevents over discharge and is explained in paragraph 2.3.

20
Fig.2.4 Block diagram representing the circuit schematic of a shunt type [39]
Due to the reduced complexity of the system, most CCs used to provide energy access are
of this kind. Figure 2.5 shows an example of current and voltage variation in a system
controlled by a shunt type CC over a 24-hour charge/discharge cycle.
In Figure 2.5, curve 1 represents the variation of PV module current, curve 2 the
variation of current input to the battery, curve 3 depicts variation of PV module voltage
and curve 4 the variation of the average battery current with respect to time.

21
Fig. 2.5 Current variation (top) and voltage variation (bottom) in a system operated using a shunt type
Interrupting Charging CC [41]
The charging cycle starts around 7 AM as sun irradiance begins to rise. It is observed that
the battery current (blue curve of top Figure 2.5) also rises correspondingly, but when
3
4
1
2

22
regulation starts (i.e. around 12 PM) the battery current starts decreasing to a value close
to zero at the sunset (i.e. around 6 PM). As soon as the charge controller begins to work,
the module is short circuited and it is utilized only for finishing charge (i.e. peaks on the
blue curve), and the load is completely absorbed by the battery.
When the Figure plotting the voltage is considered, it is observed that the voltage of the
battery (blue curve of bottom Figure 2.5) is around 12 V at 4AM, when the CC
disconnects the load. After sunrise, voltage starts to increase linearly and reaches its peak
around 12 PM, when regulation begins again. From that point on, the voltage of the
battery fluctuates, while the voltage of the module reduces and supplies power to the
battery intermittently. The difference between the current supplied from the module and
the current sent through to the battery is dissipated in the form of heat.
Instead, in Series type CC, the control is put in series with the module as observed from
the block diagram presented in Figure 2.6. In this case, when the controller recognizes the
battery as fully charged the control is switched off and the circuit is open. The PV
modules stop charging the battery and their voltage reach the open circuit value (VOC).

23
Fig. 2.6 Circuit representation of Series type CC [39]
As observed from the left plot of Figure 2.7, the series type CC essentially regulates the
incoming current of the module (red curve). Comparing the current of the module and
that of the battery, it is observed how similar these values are, while the module current
modulation does not exist in the shunt type CC. It implies higher energy wastage in the
shunt type CCs. When the regulation begins, the current in the array decreases because it
is used for charge topping.
In Figure 2.7, curve 1 represents the variation of PV module current, curve 2 the
variation of current input to the battery, curve 3 depicts variation of PV module voltage
and curve 4 the variation of the average battery current with respect to time.

24
Fig. 2.7 Current variation (left) and voltage variation (right) in a system operated using a series type
Interrupting Charging CC [41]
The array voltage approaches VOC (open circuit voltage) of the module. The regulation
voltages are usually lower for series type CC than shunt type CCs. Battery is charged at a
lower capacity in series CC compared to shunt CC [41]. These devices are more efficient
1
2
3
4

25
than the shunt type devices and provide better control, but are more expensive and
complex than their shunt type counterpart. It can be seen that the current from the module
(red line in the left curve) decreases close to zero as soon as regulation begins. This
prevents wastages of energy from the module.
A further classification of the charge controller takes into account the charging algorithm
employed. Interrupting Charging (ICH) and Constant Voltage Charging (CVC) can be
found in both Shunt and Series configurations as shown in Figure 2.3. ICH CCs are
usually referred to as pulsing CCs as they send the current from the PV module in pulses
between the two set-points. The charge controller recognizes when the voltage drops to
the lower set-point and instantly diverts power from the module. This “hysteresis” or
“pulsing” behavior is more prevalent during the later stages of each charging cycles. The
ICH shunt type CCs are the most popular and cheapest. However, their reliability,
performance, and associated lower battery life are worst compared to series CCs. Instead,
in the CVC types, the power from the PV modules supplied to the circuit depends on the
irradiation conditions, while the power supplied from the CC to the battery is at constant
voltage. This is done by a modulation circuit within the CC that allows for a constant
input to the battery. Then, the internal algorithm and control mechanism in this CVC
converts the supply power from the module to another one suitable for the battery by
modulating the current and keeping the voltage constant.

26
2.2.2 Maximum Power Point Tracking (MPPT) and Pulse Width Modulation
(PWM) Circuits
Selecting an appropriate theoretical charging model is beneficial as PV modules and
batteries operate with different voltages. This difference defines the kind of algorithms
that should be selected for charging the batteries. A brief review of two of the most
common models: Pulse Width Modulation (PWM) and Maximum Power Point Tracking
(MPPT) technology are discussed in this section. In the PWM model, the solar array and
batteries are in direct connection. The CC intervenes only to ensure that the charging is
consistent and conforms to the set-points. On the other hand, the Maximum Power Point
Tracking mechanism optimizes both power extraction from module, by using the MPPT
algorithm, as well as the power delivery to the battery. A detailed explanation and a
comparison between these two charging algorithms is presented here.
I-V (current – voltage) curves are characteristic features of a PV module. A qualitative
example of this kind of curves is shown in Figure 2.8. The solar module has a particular
voltage and current value when the power output is maximum. These current and voltage
values are called Imp and Vmp respectively. If the current and voltage values provided
from the PV module are not equal to its the theoretical values Imp and Vmp, it means that
the module is not operating optimally. The Vmp of a typical module is approximately 15-
17 V, while a 12V battery has an operating range between 10-15V [42].

27
Fig. 2.8 Theoretical I-V curve of a solar module [43]
In the case of PWM CCs, there is a direct connection between the module and the battery
as shown in Figure 2.9. This means that the module will have to supply energy in the
operating of the voltage range of the battery, so the energy from the module is not
extracted efficiently and as a result, the module’s efficiency factor is reduced. In this kind
of configuration, there is no intervention from the CC unless it is used to maintain set-
point conformity.
Fig. 2.9 Schematic of a generic PWM CC [42]

28
MPPT models are widely used in modern inverters in solar installations. A MPPT CC
embeds two printed circuit boards (PCB) with different functionalities as seen in Figure
2.10. One PCB (i.e. input board) is constantly trying to extract the maximum energy out
of the modules, while the other (i.e. charge board) is monitoring the battery level to make
sure that the supplied voltage and current values are conform to the default set-points.
Since MPPT CCs are more complex than PWM CCs, they are more expensive. A MPPT
CC is a DC-DC converter in its simplest format. Since the solar module output voltage is
not the same as that required by the battery, the MPPT CC is required to convert the
voltage from a higher value to lower one that can be stored in the batteries. It is done by
increasing the current over time and charging the battery at a higher current. The coil in
the center shown in Figure 2.10 is an inductor which serves as a DC-DC converter. Its
purpose is to supply uniform DC output given a particular DC input.
Fig. 2.10 Schematic of a generic MPPT CC [42]
Studies have determined that the MPPT CCs work marginally better than PWM CCs
under clear sky or unshaded environment, while the MPPTs’ performance can be as high
40% over traditional PWM mechanism when 1/3rd
of the module’s surface is covered
[42]. During clear sky periods, the MPPTs perform around 8% better than PWMs. This
same study argues that, despite efficiency increase during clear day is not significant,

29
over a longer time the cumulative savings makes the MPPT a worthwhile choice. Since
MPPTs convert voltages, the greater the difference in voltage is, the better these devices
will perform over PWMs. On the downside, the extent of deterioration due to increased
charging current is uncertain. For these reasons, it could be stated that the MPPT CCs are
better suited for larger systems where efficient modulation becomes a feature of
importance. For smaller systems, the gain in efficiency by use of MPPT CCs over PWM
CCs is not very significant. Table 2.1 summarizes the comparison of PWM and MPPT
CCs.
Table 2.1Comparison of the different features of PWM and MPPT CCs
Parameter MPPT CC PWM CC
Power extraction from the PV
module
Active Absent
Regulation of charge to the
battery
Active Active
Complexity Complex Relatively simple
Performance in cloudy weather More efficient Less efficient
Cost Expensive Cheap
2.3 Voltage set points
LA (Lead Acid) storage devices need to be charged in a predetermined fashion. How the
battery must be charged is specified by the battery manufacturer and executed
accordingly to an algorithm controlled by the CC. Charging cycles can generally be of 2-
stages or 3-stages.

30
Before discussing in detail the charge cycle specifications, a brief introduction of set-
points is presented for the ICH type chargers described in paragraph 2.2. Set-points are
extremely important as they provide the CC with basis of operation. If set-points are
misjudged, or wrongly measured, it causes the battery to operate a smaller number of
cycles than expected due to improper charging and excess depletion of capacity during
discharge. Set-points are determined based on a number of factors such as time required
for charging, life of battery expected, type of battery chemistry utilized, CC
characteristics, and cost of the equipment. Table 2.2 defines some of the terms that will
be used throughout this thesis. Recommended set-points for different battery types are
summarized in Table 2.3 [39]. In particular, Table. 2.3 shows the Voltage Regulation
(VR) and the Voltage Regulation Reconnect (VRR) values recommended for various
kind of batteries. It should be pointed out that the values of VR and VRR presented in
Table 2.3 are intended for 2V single-cell batteries and were provided for understanding
their order of magnitude only. This study will focus on the LA Absorbed Glass Mat
(AGM) class of batteries, where the electrolyte is not free flowing but it is absorbed on
the surface of layers of glass mats. In older batteries, the electrolyte is a free flowing
liquid. For the purpose of this thesis, only AGM LA batteries are discussed since these
are prevalent in stand-alone PV systems for their ability to deep cycle.

31
Table 2.2 Definition of the commonly used set-points
VR
(Voltage
Regulation)
This is the highest voltage that the charge controller will let
the battery reach. If the voltage of the battery measured by
the CC reaches this point, the CC will shut off the incoming
power from the module.
CHARGE
CYCLE REGULATION
VRR
(Voltage
Regulation
Reconnect)
When the battery voltage drops from VR to VRR, the CC
reverts the flow of energy from the module into the battery.
VRH
(Voltage
Regulation
Hysteresis)
The topping charge happens between VR and VRR. The
resulting on/off is the hysteresis referred to previously (§
2.2.1). Depth of the topping charge and duration may vary
drastically. Current is tapering during this time.
LVD
(Low Voltage
Disconnect)
As the battery reaches this point, the CC does not allow
further discharging of the battery. The battery has been
drained to the point that any further reduction of voltage
will damage the battery. LVD is typically chosen not too
low so that life cycles can be maximized.
DISCHARGE CYCLE
REGULATION
LVR
(Low Voltage
Reconnect)
When the apparent battery voltage increases to LVR the
load is connected and supplied with energy. LVR is reached
upon resuming of the charging state.
Self-
Consumption
During operation, the CC consumes some energy for its
own processes.
PERFORMANCE
CHARACTERISTIC

32
Table 2.3 Typical Set points for a Lead Acid battery [39]
To finish, Figure 2.11 illustrates the hysteresis cycle in the regulation (Voltage
Regulation Hysteresis) and disconnection regions (Low Voltage Disconnect Hysteresis)
described in Table 2.1.
Fig. 2.11 Illustration of hysteresis in the regulation and disconnection regions of a typical charge-
discharge cycle [39]

33
During the charging phases, the batteries receive power from the PV modules and
increase their voltage up to the Voltage Regulation point; after this, the CC disconnect
the flow of energy from the PV module to the battery and the voltage decreases up to the
Voltage Regulation Reconnect point because of inefficiencies in the charging process and
self-discharge mechanisms. As soon as this point is reached, the CC reconnect the two
sections of the circuit and the power rises to VR again. Instead, in the discharging phases
as soon as the battery’s voltage drops to the Low Voltage Disconnect point, the CC
disconnect the load from the battery and the voltage raises to the Low Voltage Reconnect
point. It should be observed that the discharging hysteresis is not as accentuated as the
charging one.
2.4 Battery fundamentals
This section will introduce the reader to some useful conceptual definitions of batteries
which shall be used repeatedly through this work. Generic definitions are presented here
and the same shall be used where necessary with appropriate substitutions.
Capacity: It is the quantity of the energy stored in the battery and it is commonly
measured in Ampere-Hours (Ah). As a solar system is designed, the capacity of
the battery has to be selected by taking into account the number of hours of stand-
by or autonomy, the loads being catered to, the available sunlight hours, and the
depletion of battery.

34
Depth of Discharge (DoD): It represents the amount of energy that can be safely
extracted out from the battery without affecting the future storage capabilities and
it is expressed as a percentage. Higher values of the DoD mean higher possibility
of irreversible failure. With each charging/discharging cycle, a minute reduction
in the actual capacity is observed. Usually, a 12 V battery reaches its end-of-
discharge state at around 10.5 V [44]. This means that at 10.5 V, the DoD is 100%
and the battery cannot longer be used without charging. Generally, DoD is
evaluated by measuring the voltage, but this parameter is not a fair indicator.
Therefore, internal resistance or specific gravity of the electrolyte serve as better
indicators.
C-rate: It is the number of Amperes that a battery can supply constantly for a
given time. For example: If the C rating is C/2 (i.e. 0.5C), the battery supplies 0.5
A for 2 hours [34]. As a result, a battery can supply a lower current for a longer
time or a higher current for a shorter time.
Sulphation: It is the phenomenon of Lead Sulphate (PbSO4) crystal depositions
on the cathode embracing some of the active area, which reduces the battery’s
capacity and performance [45]. It is a very common phenomenon for not
completely charged batteries such as the ones supplied with intermittent energy
from solar or wind. These sources, because of their discontinuous nature are not
able to supply enough energy for a full saturated charge. Sulphation can be
reduced by charging the battery properly for the whole duration specified by the
manufacturers without interruptions. Sulphation-preventive measures are
employed near the end of the charging cycle [39].

35
Life cycles: It is the time a battery can operate without much dissimilarity from
its original performances. This time can be quantified in terms of operational units
of cycles and represents the number of cycles until the capacity of the battery of
providing energy reaches 80% of its initial value.
Lifetime: It indicates how long the battery will last being loaded at a specific rate
[36] and can be evaluated using equation (1).
𝐿𝑖𝑓𝑒𝑡𝑖𝑚𝑒 𝑖𝑛 ℎ𝑜𝑢𝑟𝑠 =
𝐵𝑎𝑡𝑡𝑒𝑟𝑦 𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦 (𝐴ℎ)
𝐿𝑜𝑎𝑑 𝐶𝑢𝑟𝑟𝑒𝑛𝑡 (𝐴)
(1)
Charge factor: Takes into account that not all the energy supplied for the battery
is utilized to replenish the depleted capacity consumed by the loads [47]. Some
energy is lost because of thermodynamic inefficiency, chemical losses, heat and
internal resistance.
𝐶ℎ𝑎𝑟𝑔𝑒 𝑓𝑎𝑐𝑡𝑜𝑟 =
𝐶ℎ𝑎𝑟𝑔𝑒 𝑒𝑛𝑒𝑟𝑔𝑦 (𝐴ℎ)
𝐷𝑖𝑠𝑐ℎ𝑎𝑟𝑔𝑒 𝑒𝑛𝑒𝑟𝑔𝑦 (𝐴ℎ)
(2)
Sometimes in the evaluation of the battery’s efficiency, this factor of safety is also
considered in and results obtained from equation (1) are multiplied by this value
for improving the accuracy of the evaluation.
Gassing: Refers to electrolysis of water at the end of the charging cycle. Some
amount of controlled gassing is helpful to extend battery life, while gassing for
extended periods or shortened periods may result in faulty battery operation and

36
lower life [29]. Gassing helps by stirring the electrolyte solution to make it
homogenous.
2.5 Charging-discharging cycle plots
Charging-Discharging Cycle Plots (CDCPs) are graphical representation of voltages and
currents the battery assumes over time. They are representative of the battery
characteristics. Usually, these plots start from the fully charged battery and proceed until
the complete exhaustion of the charge under the supervision of a CC. Then the process
inverts and the battery is fully recharged to its initial state. Figure 2.12 (left) plots the
theoretical charge cycle diagram for a 2V battery and the adjoining figure (right)
represents the CDCP of a 12V LA battery, the different stages are labelled.
Fig. 2.12 3-stage theoretical charge cycle [48] (left) and CDCP of a 12V LA battery [49] (right)
In particular, the left image refers to a three-stages charging cycle, which is the most
recommended by manufacturers because a longer cycle makes the battery last longer,
while the right image refers to whole discharge and discharging cycle. The main aim of
this thesis consists in extracting the CDCPs when different CCs are used under different

37
loading conditions and to compare the obtained results with these theoretical curves.
With reference to the different sections shown in the right images of Figure 2.12, the
typical charge and discharge stages are described below:
Bulk Charging – Constant Current Charging (CCC): The battery has a State
of Charge (SoC) equal to 0% (100% DoD) as the charging is started. The battery
rapidly absorbs energy from the module and its voltage rises fast. Most of the
capacity depleted due to loading is recovered here. The voltage rises almost
linearly while the current remains more or less constant (as observed from the
first Stage depicted in the left image of Figure 2.12). This stage is not very
important since the delicate processes of topping up, gauging level of full charge,
and prevention of sulphation are not prevalent in this phase. During the bulk
charging time, the voltage need not to be continually monitored, hence on/off
cycling of the ICH CCs is not noticeable. The CDCPs of the experiments
conducted for this work will have Variable Current Discharge (VCD), since the
LED loads consume varying currents depending on the input voltage.
Absorption Charge – Constant Voltage Charge (CVC): At this point, the
battery has absorbed much of its charge. It now needs to complete the process by
fine-tuning itself. The CC starts monitoring the battery charges by sending the
charge into the battery at a controlled rate. The current will start to taper while
voltage is now constant (Stage 2 in left image of Figure 2.12). The ICH CC now
starts to closely monitor the battery to charge it slowly but thoroughly. Slow
charging is used to replenish the charge lost due to inefficiencies as previously

38
mentioned. This operation is also responsible for countering effects of sulphation.
In this section the hysteresis phenomenon described in the previous paragraphs
happens.
Float Charge or Charge Idle Time (CIT): During this stage, the CC maintains
the battery level constant by diverting current at a lower voltage. This is done to
compensate for the self-discharge phenomenon inherent to batteries.
Constant Current Discharging (CCD): In this stage, the load is connected and
the battery keeps supplying power until it reaches the LVD value described in
Table. 2.2. The curve’s profiles are very smooth and do not change much for
different CCs or batteries, while the slopes of the profiles depend on the
connected load.
Discharge Idle Time (DIT): After the battery is fully discharged it is no longer
operating. Voltage increases slightly due to termination of current extraction and
the battery is now idle until charging is started again.
Ideally, the charging process needs to provide the charge lost when the battery is
connected to loads, compensate for the energy lost due to the thermodynamic cycling,
and control the gassing at the end of the cycle to prevent stratification phenomena.
Therefore, these diagrams are extremely useful as they allow evaluating some
characteristics of the CC such as:
1. Conformity of the CC cycle to the theoretical model.
2. Comparison of performance of different CCs.

39
3. Lifecycle cost simulation of the CCs.
Using the analysis of CDCPs it is possible to understand their behavior from an
electronics standpoint and validate the performance claimed by the manufacturers.
2.6 Observed issues
During some preliminary tests performed to evaluate the characteristics of the CCs, it was
observed that they did not behave exactly as predicted in the manuals. Often the
information was inaccurate and in most cases insufficient for modelling or comparison
purposes. This is especially true with cheaper devices. These problems served as an
inspiration to devote full-fledged efforts into understanding these devices and are the
main motivation behind this thesis. The characteristics of the charge cycle being utilized
are not mentioned by the manufacturers.
After performing a few trials, it was noticed that the CC behavior is quite fluctuating too.
The charge profiles of subsequent tests with same battery and conditions seemed to yield
a slightly different curve. The same was observed when multiple units of the brand and
product line were compared. As mentioned before, conformity to the set-points and
theoretical CDCPs are crucial for long life of the battery. Therefore, a better
understanding of these problems is a highly desired to determine whether or not these
devices are suitable to be employed as reliable, low maintenance controllers for the
production of energy in remote and developing areas.

40
III. METHODOLOGY
3.1 Overview
The main objective of this work is to document the behavior of different types of CCs
and to understand which one is suitable for the installation within a PV system in remote
and developing countries. For this purpose, five different products were selected based on
their cost and technical specifications. Having reviewed the products available on the
market, it was decided to test CCs that are sold over a $10-$70 price range.
This thesis has two different components: an evaluation of the experiments performed
under different loading conditions and a simulation of the LCC. The experiments include
a characterization of the CCs both in absence and presence of loads to obtain the CDCP
for each device under the different loading conditions. In the first set of experiments the
CCs were tested without the application of simultaneous loads, while in the second set of
tests a simultaneous load representing a cell-phone being charged was added. CDCPs
with simultaneous loading were evaluated to characterize the performances of the devices
and compare them with those measured when no loads were applied. These data would
be helpful to estimate performance characteristics. Both experiments rely on very a
simple setup. In the first one a PV module (during charging phases), a LED strip (during
the discharging phases), and a battery only were used; while the same three components

41
and a cell-phone battery equivalent (i.e. a portable battery charger whose performance
and behavior approximate the behavior of a charging cell-phone) were employed in the
second one. During initial stages of the project, a Power Source (PS) was used to supply
the CC with energy in order to simulate the current production from a PV module. As
mentioned in the previous chapter 2.6, the CC’s behavior was negatively affected by the
PS. Hence, a 30W PV module was used to supply the CC with energy. The tests done
using the PS will not be discussed in detail in this work for the sake of brevity. To finish,
a simulation of the lifecycle costs was performed considering the non-conformity to the
theoretical set-points and other flaws affecting battery life cycles highlighted during the
experimental analysis.
3.2 Equipment used and experimental setup
Before presenting the details of the experimental setup, an understanding of the
equipment and experiment details is provided.
Before starting any test, the used battery was depleted to the LVD level and then charged
using the Werker Class 2 Battery Charger shown in Figure 3.1 [50]. It provides a 12V
output at 1A [50].

42
Fig. 3.1 Werker battery charger used to replenish the battery before starting each experiment [50]
The device switches off automatically once the battery is fully charged and has a LED
indicator to show the SoC of the battery. This procedure has been applied to ensure that
the battery has nearly the same amount of energy stored in it before starting each
discharging cycle and to ensure similar initial conditions in each of the tests performed.
In the first set of experiments, when the batteries are fully charged, a 12-hour discharge
cycle test is undertaken using a LED strip as a load. The CCs prevent over discharging
the batteries by shutting off the load. At the end of the 12-hour discharge cycle, after
resting the system, a 12-hour charge cycle is started using the PV module powered by
two 1kW incandescent lamps. This process was repeated for each of the 5 selected CCs.
In addition, for proving the experiments’ repeatability, two same-brand devices for each
of the five selected CCs were tested. A total of 10 surveys have been performed for the
first experiment set. The second experiment followed the same procedure, but a cellphone
battery equivalent was added in both the charging and discharging phases.

43
3.2.1 Lighting and current sources
As stated in the previous paragraph, energy was supplied to the system through a PV
solar module. To operate the 30 W PV module (Figure 3.2), two 1 kW lamps similar to
that shown in Figure 3.3 were used.
Fig. 3.2 30W solar module selected [52]
Fig. 3.3 Arrilite 1000W lamp
This solar module was selected because of its well-known electric characteristics [51] and
because of its low power [52], which makes it suitable for low-income and developing
areas. Furthermore, its nominal capacity is close to that normally used by households for

44
the dual purposes of lighting and cell phones charging. The module and the system would
be operated for quite a few years making the recovery of cost much more foreseeable and
realistic. In addition, the module could easily be used for catering slightly expanded
system capacity if desired by the user.
To extract the maximum current from the module, numerous spatial adjustments were
made. 1.6 A of current was extracted from the illuminated module which corresponds to a
charging C-Rate of around 0.114C. Also around 20-25 W of power were extracted from
the module during the course of the whole charging period. Despite the module was rated
at 30 W at 1000 Wm-2
, the maximum illumination that could be simulated using the
lamps was between 666-833 Wm-2
. As soon as the lamps were turned on, nearly 20W
was extracted and the module supplied this energy at a voltage between 12 and 12.5 V.
Probably, this variation depends on changes in the module input voltage over the
charging period, which is function of the battery properties.
From an analysis of the recorded CDCPs, it was found that the current extracted from the
modules remained almost constant through the bulk charging period, while the voltage
raised. Furthermore, during the tests, measurements of the temperature of the CC were
made regularly using a thermocouple to be sure that its operating temperature did not
significantly vary from room temperature and no temperature compensations were
required by the CC itself.

45
3.2.2 Current and Voltage measurements
The performed experiments rely on the measurement of both current and voltage. In
particular, for the first set of experiments two currents and two voltages values were
recorded through the whole duration of the test; while for the second set of experiments,
three currents and three voltages values were recorded.
To record the current output of each component in the system, current transducers were
used to convert component currents into voltages because the Data Acquisition (DAQ)
hardware used could only record voltage values as inputs. These transducers were
powered using a 24 V power source supplying between 17 and 20 mA per each device.
By diverting a current carrying conductor through the loop of the transducer, it was
possible to obtain a voltage output corresponding to the magnitude of the current flowing.
In Figure 3.4 the transducer employed is depicted, while Figure 3.5 shows the calibration
chart of the transducers employed, which shows a linear relationship between current and
voltage values.
Fig. 3.4 CR5210-5 DC current transducer [53]

46
Fig. 3.5 Performance curve of the CR2510-5 transducer
To acquire the voltage values, a NI USB-6001 DAQ [54] manufactured by National
Instrument and managed using a customized LabView code was used. Figure 3.6 shows a
picture of the DAQ and the block diagram of the executable code used.
Fig. 3.6 NI USB-6001 DAQ device [54] (left) and NI LabView block diagram for data-acquisition (right)
Furthermore, since the selected DAQ cannot measure voltage input greater than 10V and
considering that the PV module-battery system output may provide output voltage in the
order of 15-17 V, it was decided to use voltage dividers to obtain only half of the input
voltage and prevent any potential damage to the DAQ. The electrical circuit diagram of
the voltage divider that was used is depicted in Figure 3.7 and for each of the DAQ
0
1
2
3
4
5
6
0.25
0.5
0.75
1
1.25
1.5
1.75
2
2.25
2.5
2.75
3
3.25
3.5
3.75
4
4.25
4.5
4.75
5
OutputVoltage(V)
Current input (A)

47
channels used for acquiring voltage values, a divider was used. During the tests, data
were sampled every 30 seconds.
Fig. 3.7 Voltage divider circuit diagram
3.2.3 Battery properties
The battery selected was a Lead Acid Absorbed Glass Mat (LA AGM) type with a
nominal capacity of 14Ah or 168Wh at 12 V. This battery is sealed and does not need any
kind of maintenance. Two batteries of the exact same kind were used to expedite the
testing: a Duracell 14Ah AGM LA battery [55] and a Werker 14Ah AGM LA battery.
These batteries are suitable for being used in SHLS units since they are deep cycle
batteries capable of depleting to lower SoCs than the conventional LA batteries.
3.2.4 Charge controllers
The CCs are the most important component of the entire experimental process. As stated
before, the aim of this work is to understand how the different kinds of CCs behave. For
this reason, 5 different devices were purchased to be tested. Table 3.1 shows the pictures

48
of the different devices, while Table 3.2 summarizes their specifications and battery-
protective features. The abbreviations mentioned in Table. 3.1 are used for distinguishing
the CCs of different brands.
All of the information summarized in Table 3.2 have been taken from the products’
datasheet, while the eventual blank spaces represent either ambiguous data or missing
information. Furthermore, it has been observed that the datasheets of the cheaper devices
lack important information.
All the CCs used in this thesis are of PWM type.

49
Table 3.1 Figures of the Charge Controllers being used
Morningstar (MS)
SHS-6
Windy Nation (WN)
P10
Steca (ST)
Solsum 6.6F
CMP12(CM)
CMTP02 (CT)

50
Table 3.2 Specifications of the different CCs tested
Product name
Cost
(USD)
VR
(V)
LVD/ LVR
(V)
Self
Consumption
Other features
Morningstar
SHS-6 [56]
34.99 [57] 14.3 11.5/12.6 <8 mA
Series 4 stage PWM, reverse
current protection, high voltage
protection, short circuit and over
current protections [58]
Windy Nation
P10 [59] 21.99 14.4 11.1/12.5 <5 mA
Float at 13.6V
Equalization at 14.6V
[60]
Steca
Solsum 6.6F [61] 28.95 [62] 13.9 11.2/12.4 <4mA
Over voltage/ over current
protection, monthly maintenance
charge etc..
Boost/ equalization not specified
[63]
CMP12 9.99 [64] 14.4 [64] or 14 10.8 - -
CMTP02 [65] 22 [66] 14.4 10.8/12.6 - -

51
3.2.5 Loads
Two kinds of loads were used for the experiments. For the first set of experiments, where
the CDCPs of the CCs were obtained without simultaneous loading during the charge/
discharge period, the LED strip shown in Figure 3.8 was utilized to discharge the battery.
Fig. 3.8 LED Strips used as load
The strip has 120 LEDs and produces an illumination of around 450 Lumens which is
sufficient to light up a small hall/ kitchen. During the discharge period, it was observed
that the strips consume about 1.29 A of current, corresponding to a C rate of 0.092C. The
name of the manufacturer has not been mentioned on the product or the packaging.
For the second set of experiments, CDCPs were intended to be obtained with
simultaneous loading that means discharging the battery using two different loads (i.e.
LED and a small electronic device) and in charging them through the PV module as the
small electronic device was still connected to the grid. The load produced by the small
electronic device was chosen so as to simulate the same consumption pattern as a
cellphone. This is realistic since one can expect the user to charge a cellphone while the
entire system is charging and keep using it as the batteries are discharging. A
commercially available portable battery pack was used which serves as cell phone battery
equivalent (CBE) and it is shown in Figure 3.9. The storage capacity of this battery pack

52
was rated at 2,200mAh [67], close enough to the capacity of many medium size
smartphones.
Fig. 3.9 Portable battery pack used as cellphone battery equivalent [67]
Two portable CBEs were used during the test, connecting each of them to the system for
six hours for a total time of twelve hours. Both portable chargers were completely
discharged before starting each test so to not have any residual charge which can modify
the energy absorption from one test to another.
Step down bucks were used to charge the above mentioned CBE through an Universal
Serial Bus (USB) port supplying a constant voltage of 5V (Figure 3.10 [68]).
Fig. 3.10 A step down buck used to charge the power bank [68]

53
A step down buck converter is basically a DC-to-DC converter which takes the energy in
output from the CC and transforms it. The current fed through the CC to the step down
buck was acquired also acquired to control its variation over time. At the end of the sixth
hour, once the CBE was fully charged, it was replaced with the other one. The newly
removed CBE was then discharged using a power resistor similar to that shown in Figure
3.11 and kept ready for the next test [69].
Fig. 3.11 CBE discharging power resistor [69]
3.3 Experiment 1: Setup of the CDCP experiment with no CBE
Aim of this experiment is to evaluate how the CCs behave during the charging of LA
battery when no loads are connected to the CC and to evaluate the behavior of the same
device as a LED strip is used for discharging the battery. The schematic of the
experiment, both for the discharging and the charging cycles is presented in Figure 3.12
and 3.13.

54
Fig. 3.12 Schematic of the discharging cycle
Fig. 3.13 Schematic of the charging cycle

55
During the discharging phase, when only the LED strip was connected to the battery
through the CC, the residual voltage of the battery (Vb), the output voltage of the LED
strip (Vl), and the respective current values (Ib and Il) were acquired using the DAQ.
During the charging phase, the voltage of the battery (Vb), the output voltage from the PV
module (Vm), and the respective current values (Ib and Im) were acquired using the DAQ.
CDCPs for 10 devices were obtained, one each for the charging and discharging cycles.
A total of 20 data sets were obtained for the first set of experiments (EXP. 1) and the
collected data helped further analysis.
3.4 Experiment 2: Setup of the CDCP for the simultaneous loading case
The second sets of experiment (EXP. 2) is more complex than EXP. 1 due to the addition
of the Cellphone Battery Equivalent (CBE). Figure 3.14 shows the schematic for EXP. 2
and highlights the six channels of data recorded for this experiment.
During the discharge cycle, a fully charged LA was discharged using the LED strip in
addition to a fully discharged CBE in parallel. The discharge rate in this case was higher
than the previous case. After six hours, the CBE was replaced with another CBE which
had been already been fully discharged using the power resistors depicted in Figure 3.11.
The solar module was not illuminated during the discharging phase.

56
Fig. 3.14 CDCP with contemporary loading
During the charging phase, the module was illuminated using the 1000W lamps while the
CC supplied a portion of this energy to the CBE that was connected in tandem. A total of
20 CDCPs were obtained from EXP. 2.
The setup used for performing EXP. 2 is shown in Figure 3.15 and 3.16. In particular
Figure 3.16 shows a detail of the setup with particular emphasis on the devices used (i.e.
transducers, LA battery, stepdown buck, CBE, bread board on which the voltage dividers
were mounted and the LED strip).

57
Fig. 3.15 Entire experimental setup (1) PV module, 5) Digital multimeter)
Fig. 3.16 Detail of the experimental setup (2) Current to Voltage Transducers, 3) DAQ, 4) Voltage dividers on breadboard, 6) LA Battery, 7) CC, 8) LED strip,
9) CBE, 10) Step down buck)
1
5See Fig. 3.16 for
enlarged area
7
+
6
3
1
8
9
4
2

58
The lab was maintained at 70-75ºF whenever the experiments were running. This was
done to reduce the impact of the temperature compensation during the charging phase. A
computer was the repository of the data recorded by the DAQ unit. A HP 24V Power
Source (PS) was used for supplying the three transducers connected in series to it.
The entire list of equipment using both tests is given in Table. 3.3. Table. 3.4 shows the
whole set of experiments that were performed. As can be seen, the abbreviations
introduced in Table. 3.1 are utilized.

59
Table 3.3 List of components used
Equipment used
Number of
units
Experiments utilized
Equipment
utilization phase
Illumination
Arrilite 1000W lamps 2 EXP. 1&2 CH only
Charging source
30W altE poly PV module 1 EXP. 1&2 CH only
Measurement and acquisition
CR Magnetics CR5210-5
current transducer
2 EXP. 1 CH & DIS
3 EXP. 2 CH & DIS
NI USB-6001 DAQ 1 EXP. 1&2 CH & DIS
Voltage dividers
2 EXP. 1 CH & DIS
3 EXP. 2 CH & DIS
Multimeter 1 - -
Storage and control
14Ah AGM LA battery 2 EXP. 1&2 CH & DIS
Charge controllers 10 EXP. 1&2 CH & DIS
Loads
LED strip
(during discharge only)
1 EXP. 1&2 DIS only
Cell Phone Equivalent
(only in the EXP.2)
2 EXP. 2 only CH & DIS
Auxiliary
Stepdown buck 2 EXP. 2 only CH & DIS
HP 24V Power Source
(for transducers)
1 EXP. 1&2 CH & DIS
Bread board
(for mounting voltage dividers)
1 EXP. 1&2 CH & DIS
Legend
EXP. 1 Experiment 1
EXP. 2 Experiment 2
CH Charging cycle
DIS Discharge cycle

60
Table. 3.4 Test matrix
Test
name
Test description Morningstar Windynation Steca CMP12 CMTP02
DISCHARGING PHASE
EXP.1
(DIS)
A fully charged battery is gradually depleted till
LVD in supervision of a CC using a LED strip as
the load.
MS01 WN01 ST01 CM01 CT01
EXP. 2
(DIS)
A fully charged battery is depleted in supervision
of a CC using a LED strip together with a fully
discharged CBE connected in parallel. CBE
replaced after 6 hours.
CHARGING PHASE
EXP. 1
(CH)
The charging of a depleted battery (respective
preceding discharge cycle) managed by a CC
while energy is supplied from the illuminated PV
module.
EXP.2
(CH)
The charging of a depleted battery (respective
preceding discharge cycle) managed by a CC
while energy is supplied from the illuminated PV
module and simultaneously charging a CBE. CBE
replaced after 6 hours.

61
3.5 Theoretical model to estimate lifecycle cost
A theoretical model of a CDCP was created with the purpose to compare the measured
performances with the ideal behavior of a LA battery. There are many models that have
been used for simulating the characteristic performance of Lead Acid batteries [70]. The
most simplistic model is essentially a voltage source in series with a constant resistance
which represents the internal resistance of the battery. But the assumption of a fixed
internal resistance is major drawback since in reality, the internal resistance varies with
the state of charge and electrolyte concentration (Durr et al. [71]). Another drawback of
the model is the assumption of unlimited battery capacity. Therefore, other models were
developed which give a better picture of the battery’s CDCPs.
One of these is the dynamic battery model; a more complex, realistic, and accurate model
which is widely used to simulate battery behavior. Figure. 3.16 shows the schematic
representation of the dynamic battery model. The elements are modelled non-linearly and
regulated using the battery’s open circuit voltage (Voc), which is indirectly a function of
the State of Charge (SoC).
Fig. 3.17 Dynamic battery model utilized (source: [70])
In particular, the elements shown in the model assume the following meaning:

62
- Cb is the battery capacitance.
- Rp is the self-discharge resistance which takes into account the current small
leakage.
- Ric and Rid are the internal resistances during the charging and discharging
respectively, they account for the losses in the electrolyte as well as the
battery plates.
- C0, Rc0 Rd0 are the components of a branch of the circuit that accommodates
for the voltage drop as soon as the battery is connected to a load as well as
for over potential factors.
The non-linear equation used for the modelling of each of the above mentioned
components is described in equation (3).
𝐵𝐸 = 𝑘 × 𝑒(𝑊×(𝑉 𝑚−𝑉𝑜𝑐)) 𝑓𝑓
(3)
BE represents each of the battery elements shown in Figure 3.17 (i.e. Cb, Rp, Ric, et.), while
k represents the gain factor, W the width factor, Vm the mean voltage, VOC the open
circuit voltage, and ff the flatness factor. The characteristic values for k, W, and ff are
taken from the theory and are different for each of the elements considered and
depending on the charging/discharging phases also. The flatness factor is assumed equal
to 2 for the purpose of this model. These constants have been derived from a work made
by Casacca [49, 72] and can be found tabulated there. Vm for this kind of battery is taken
as 12.4 V. A MATLAB model was created for the purpose of obtaining theoretical
CDCPs.

63
IV. RESULTSAND DISCUSSIONS
4.1 Overview
The CDCPs of the two experimental tests are presented as well as the LCC calculation
for each of the CCs. From the experimental data it was found that the CCs possessed
some variability. Some of them included boost or floating in the charging phasing while
others totally circumvented these stages. Individual plots for the currents and voltages are
also presented. Finally, a list of important characteristics is made and then discussed to
gain a better understanding of the collected data.
Prior to beginning of the comparisons, a brief description of some of the desired
characteristics is presented here and those features will be used for evaluating the
performances of the CCs later in this chapter. It should be noted that sometimes general
guidelines and recommended trends are given in those cases where specific values are not
available. This is because the Universal Standards and Lighting Global SHS standard do
not mention specifics for flooded AGM batteries, though these standards provide
adequate information for the set-points of other types of batteries.
LVD: As described in Chapter 2, the Low Voltage Disconnect is the value at
which the CC cuts off the power supply from the battery to the loads. This set-
point must not be too low as lower value results in excessive discharge and

64
therefore in a shorter battery life. Also, lower the LVD is, the longer it takes to
fully charge the battery assuming a completely discharged unit. It is
recommended by Lighting Global SHS Kit guidelines to set the deep discharge
disconnect at 1.87 V/cell for a flooded LA battery, which corresponds to 11.22 V
for the six cell 12 V batteries used in this work [35].
Discharge time: It is the amount of time the battery can supply a load at a
specified C-rate. In the case of two CCs of the same kind (e.g. brand, model, type,
etc.), this value must be similar. Similar values of discharge time are an indication
of repeatability and a feature attesting good performance for a given CC type.
Self-consumption: This parameter represents the difference between the energy
supplied and the energy diverged to the battery. If too much power supplied to or
from the battery is wasted, the overall system efficiency is reduced. The value of
this parameter should be kept as low as possible for overall efficient operations.
Charge factor: It is the ratio between the energy supplied to the battery and that
depleted during the discharge phase. The charge factor needs to be at least
between 1 and 1.05 for SHS [24].
Reverse current protection: All CCs must compulsorily provide protection for
the back flow of power from the battery into the PV module [24].
Conformity to set-points: For commercially available CCs the measured set-
points must be within 1% of the manufacturer specified values [24] for assuring a
good quality and accurate cycling.

65
Charging limit voltages: It a region defined by the following parameters: boost
voltage (2.4 V), VR (2.35 V) and VRR (2.20 V) [39].
4.2 Results: EXP. 1
The procedure and details of the setup for this experiment is presented in Section 3.3.
The CDCPs for all the devices are presented in the same graph for an easier comparison
of their performances, while individual CDCPs for each of the CCs used during the first
set of experiments (EXP. 1) are presented in Appendix 1. The current and voltage CDCP
is shown in Figures 4.1 and Figure 4.2, respectively. The first device of each kind has
been represented using a solid line of a particular color, while the CDCPs for the second
devices of the same kind has been represented using dotted lines of the same color. It
should be also pointed out that the first twelve hours of measurements refer to the
discharging cycle, while the following twelve hours correspond to the charging cycle.
It should be noted that, the obtained CDCPs for all the ten devices showed slightly
different starting voltages (in the order of ±0.2 V). It could imply different charging level
or capacity of the battery at the beginning of the test. Since the discharging profile of
each devices has been shown to be linear, it was possible to interpolate the curves to
obtain a common starting point of approximately 12.9 V. This would also give a more
realistic value for the discharge time, so that the batteries could be depleted to the same
level.

66
As can be seen in Figure. 4.3, the measured power are similar to the current curves. In all
of the devices, during charging the power curves have some variation. The most
significant variation is observed in the CT02 device which accumulates a lot of energy
during the topping/regulation phase. In most cases, the batteries are to be charged close to
80% SoC by the end of the CCC region. Surely, the power absorption of the CT01 is
lower than WN02 or MS01 during the bulk charging phase. It is possible that the device
compensates for that during the topping phase. The battery is also over charged by the
device and it is apparent in referring Table 4.1 since the CT01 device has the highest
charge factor meaning that it over charges the battery the most compared to other CCs.

67
Fig. 4.1 CDCP of the battery currents for the ten devices for EXP.1
0.0
0.4
0.8
1.2
1.6
2.0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
CurrentinA
Time in hours
CM01 CM02 CT01 CT02 ST01 ST02 MS01 MS02 WN01 WN02
12 HOUR DISCHARGING PHASE 12 HOUR CHARGING PHASE

68
Fig. 4.2 CDCP of the battery voltages for the ten devices for EXP.1
10.0
11.0
12.0
13.0
14.0
15.0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
VoltageinV
Time in hours

69
Fig. 4.3 CDCP of the power for the ten devices for EXP.1
0.000
5.000
10.000
15.000
20.000
25.000
30.000
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
PowerinW
Time in hours

70
In Figure. 4.1, the point where the current curves drop to zero is the point at which the
discharge ends. Immediately before the battery reaches this point, the CC starts
monitoring the voltage, and as soon as it is reaching the LVD set-point it shuts off the
load ending the discharging phase. Though discharging is a much simpler process
compared to charging, it can be clearly noted that there is a disparity of performances
between the devices of the same type (i.e. same color curves) as well as between CC of
different manufactures. The discharge times varied as much as nearly four hours
depending on the CC used.
From the analysis of the charging phase, it can be observed that several differences exist
between the considered CCs. One dissimilarity is the different behavior as the full-charge
state is reached. Some devices exhibited both a float charging stage and boost stage while
other devices have only one stage. This is of particular concern, since these stages are the
stages where electrochemical, thermal losses and self-discharging are accounted for.
Therefore, missing one or more of these stages may compromise the LCC of the battery.
From a more accurate analysis of the data presented in the Figures 4.1 and 4.2, it is
possible to observe that the Steca devices ST01 and ST02 (represented by the green
curves) show clearly different discharge time of 8.35 and 7.81 hours respectively. The
starting voltages were 13.02 and 12.93 V respectively, which probably is the reason for
the discharge time disparity. The LVD points were measured at 11.57 and 11.83 V which
are higher than the 11.1 V reported in the data sheet. Despite the initial SoC disparity, the
CC is nonetheless expected to cut off supply to the load exactly at the LVD point. Hence,
conformity to set-points is lacking and the cycle is shut off nearly 0.6 V before the
stipulated value. The charging profiles were quite smooth but just as in the discharging

71
profiles, there was a clear difference in the behavior of the two devices in the last stages
of the charging cycle. As seen is Figure 4.2, the float charging of the two devices were at
13.65 V and 14.08 V respectively. Despite these drawbacks, the Steca CCs manage to
have reasonably good charge factors. The self-consumption during the bulk charging
phase was noticed to be around 6.5 times greater than that allowed by the datasheet. This
characteristic seems very high and it is an undesirable factor in SHLS applications.
The Morningstar products (represented by the beige curves in Figures 4.1 and 4.2) have
the closest discharge times for both the units, hence the most predictable performance
among all the CCs when it comes to discharging. The charging profiles of MS01 and
MS02 were also observed to be very similar to each other, which is the ideal behavior of
these CCs. The performance of these devices even conform to the set-points stipulated in
the manufacturer’s data sheet. However, the self-consumption can be as much as double
to what is specified during the charging phase. Charge factor, was also calculated to be
sufficient as can be observed from data summarized in Table 4.1. Apart from the high
self-consumption, the Morningstar products seem to perform optimally and being a good
fit for SHLSs.
CM devices (the blue curves in Figures 4.1 and 4.2) were the cheapest ones among those
chosen for performing this research. Detailed specifications were not provided by the
manufacturer. The Lighting Global regulations among others, require clear and detailed
labelling of the performance set-points. CM and CT devices have the lowest theoretical
LVD set-point fixed at 10.8 V. During the tests performed the measured LVDs for the
CM01 and CM02 have been calculated equal to 11.28 V and 10.78 V. The large disparity
in the found values could be due to variations in manufacturing or because a device was

72
not working properly, but since the tests have been performed considering two units only,
no particular conclusions on the quality of the CC can be done. Nevertheless, a very low
pre-determined LVD point may have an impact on the battery life as described in the
previous sections. Also, the power wastage during charging phases was highest among
these devices.
The most diverse comparative performance in the charging phase was exhibited by the
Windynation devices (black curves in Figures 4.1 and 4.2). These devices had a disparity
of discharging times of nearly one hour and half. Most interesting was that, even if the
specification mentions a boost charge value for the battery of 14.4 V, there is no evidence
of boost charging in the profiles of WN01 and WN02. The boost charge is maintained for
nearly 30 minutes at values below 14 V, and after that is kept at float charge until the end
of the cycle. In addition to this flaw, both the devices did not charge at the stipulated float
voltage of 13.6 V. Floating was clearly noticed being around 13.12 V and 12.97 V for the
two devices being tested. Furthermore, the charge factor was calculated below 1 meaning
that the battery would expel more energy during the discharging phase than it replenishes
during the charging phase. As it easy to imagine, this behavior cannot be sustainable
since each charge/discharge cycle further depletes the residual capacity of the battery
making it useless in a very short time. The reason for this behavior can be found
analyzing the current profile plotted in Figure 4.1. Here after a stationary phase in which
the current is kept constant (i.e. between 1.6 A and 1.7 A), the CC drastically drops that
value to zero, without any transitory period as observed for the other devices. Indeed, in
other devices, a tapering of the charging current is clearly noticed.

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