TEMPERATURE CONTROLLED NiCd BATTERY CHARGER
HAZER BIN MOHAMAD SAYUTI
This thesis is submitted as partial fulfillment of the requirements for the award of the
Bachelor of Electrical Engineering (Hons.) (Power System)
Faculty of Electrical & Electronics Engineering
Universiti Malaysia Pahang
NOVEMBER, 2008
iv
ACKNOWLEDGEMENT
In order to finish this thesis, I have met a lot of people to refer or take advice, my
beloved friends, supervisor and subject coordinator. They have contributed towards my
understanding and thought about thesis writing, since this is my first time to write the
thesis so I have no experience. I wish to express my appreciation to my supervisor En
Ruhaizad Bin Ishak for encouragement, guidance, and criticism, he also responsible to
push me in order to finish my project and the thesis perfectly on time, thanks a lot to
him.
I am also very thankful to subject coordinator En Reza Ezuan Bin Samin for their
cooperation to give me a guide line of writing thesis. Not forget to En Fairuz who help
me a lot in developing the programming, he also give me a guidance and suggestion
about the temperature sensor.
To all FKEE labs staff especially En Shalmizan who gives me an excuse to get a
new PIC on last minute after mine had burn while doing the project. My sincere
gratitude also goes to Mohd Khairi Khalib, my tutor who has helped me a lot in
programming. Without all of them, my thesis will not have been as presented here.
v
ABSTRACT
Nowadays electronic gadgets are widely use due to the growth of new
technology. Most electronic gadgets use dry cell as their main energy source; this is
due to its small size, efficiencies and recharge ability. Recharge the battery can save
cost and reduce the thrown of old battery which can effect the environment.
Electrochemical reaction in battery is affected from the temperature. Connecting a
device creates a current and the electrons flow through the device to the positive side.
At the same time, an electrochemical reaction takes place inside the batteries to
replenish the electrons. The effect is a chemical process that creates electrical energy.
Once the battery nears a full charge, excess charge current becomes heat. The heat
begins to accumulate in the mass of the battery side. As the heat accumulates,
temperature of the battery begins to rise. Current through the battery begins to double
for every degree Celsius, thus more power is dissipated in the battery which means
more heat is generated, as a result more current flows which produce more heat. The
heat increase the resistance of the battery, thus the voltage loss occurs and the
charging became less efficiency as a result the optimum charging can’t be achieved.
To overcome this problem, the cooling fan is added to maintain the battery
temperature. The sensor is function to measure the battery’s temperature and driver
circuit driving the cooling fan if the battery’s temperature reaches the set value (31
ºC).
vi
ABSTRAK
Pada masa kini, alat elektronik digunakan dengan meluas kesan daripada
pertumbuhan teknologi baru. Alatan elektronik kebanyakan menggunakan sel kering
sebagai penjana tenaga utama, ini disebabkan oleh saiznya yang kecil, kecekapanya
dan keupayaan untuk dicas semula. Cas bateri dapat menjimatkan belanja dan
mengurangkan pembuangan bateri lama yang boleh memberi kesan tidak sihat
kepada persekitaran. Tindakbalas elektrokomia didalam bateri diakibatkan daripada
perbezaan suhu yang terhasil. Penyambungan litar lengkap sesebuah alat
mengakibatkan arus elektrik dan elektron-elektron bergerak melalui alat tersebut
menuju ke bahagian positif. Pada masa yang sama, tindakbalas elektrokimia terhasil
di dalam bateri dan menambah jumlah elektron. Kesan daripada proses kimia
tersebut menghasilkan tenaga elektrik. Apabila bateri hampir cas penuh, arus elektrik
daripada cas lebihan akan bertukar menjadi haba. Peningkatan suhu mula untuk
terkumpul didalam bateri. Peningkatan suhu yang terkumpul mengakibatkan suhu
bateri meningkat. Elektrik yang melalui bateri bermula untuk meningkat untuk setiap
penambahan darjah celcius, oleh itu lebih kuasa dihamburkan dalam bateri,
bermaksud lebih haba dihasilkan, kesannya tenaga elektrik yang terhasil akan
menghasilkan lebih haba. Peningkatan haba meningkatkan rintangan bateri
meningkat, oleh itu berlaku kehilangan voltan dan proses cas menjadi semakin
kurang cekap. Hasilnya cas optimum tidak akan tercapai. Untuk mengatsi masalah
ini, kipas digunakan untuk mengekalkan suhu bateri. Alat pengukur suhu digunakan
untuk mengukur suhu bateri dan litar pemandu memandu kipas penyejuk.
vii
TABLE OF CONTENTS
PAGE
TITLES
i
DECLARATION
ii
DEDICATION
iii
ACKNOWLEDGEMENT
iv
ABSTRACT
v
ABSTRAK
vi
CONTENTS
vii
LIST OF TABLES
xi
LIST OF FIGURES
xii
LIST OF APPENDICES
xiii
CHAPTER 1
INTRODUCTION
1.1
Overview
1
1.2
Objectives
3
1.3
Scope of project
3
1.4
Problem statement
4
1.5
Thesis organization
5
viii
CHAPTER 2
2.1
LITERATURE REVIEW
NiCd Cell
6
2.1.1 Introduction to NiCd Cell
6
2.1.2 Advantages
7
2.1.3 Voltages
7
2.1.4 Charging
8
2.1.5 Charging method
9
2.1.6 Overcharging
9
2.2
Thermistor
10
2.2.1
Introduction
10
2.2.2
Advantages
11
2.2.3
Disadvantages
11
2.3
PIC Microcontroller
12
2.3.1
History
13
2.3.2
Variants
14
2.3.3
Microchip Programmer
14
2.4
MPLAB
15
2.5
PICBasic Pro Compiler
16
2.6
Driver Circuit
16
CHAPTER 3
METHODOLOGY
3.1
Introduction
18
3.2
Methodology
19
3.2.1
Developing power supply and charging circuit
21
ix
3.2.2
Installation of temperature sensor
23
3.2.3
Developing LCD display circuit
25
3.2.4
Developing driver circuit
27
3.2.5
Developing PIC Circuit
29
3.2.5
Build PIC programming
30
3.3
Picture of hardware
CHAPTER 4
34
RESULT AND DISCUSSION
4.1
Introduction
35
4.2
Charging process
35
4.3
Charging temperature
38
CHAPTER 5
CONCLUSION AND RECOMMENDATION
5.1
Conclusion
40
5.2
Future recommendation
41
5.3
Costing and commercialization
41
REFERENCES
43
APPENDIXES
APPENDIX A
PIC Programming
45
APPENDIX B
PIC 16F877A Date sheet
48
APPENDIX C
High/Low Driver Data sheet
54
APPENDIX D
Thermistor TTC103 Data sheet
57
APPENDIX E
Voltage Regulator LM317 Data Sheet
59
x
APPENDIX F
Power MOSFET IRF540 Data Sheet
61
APPENDIX G
Table of price
63
APPENDIX H
Hardware of project
65
xi
LIST OF TABLES
TABLE NO
TITLE
PAGE
3.1
Voltage versus temperature
25
4.1
Time of charging with the increasing in voltage
36
4.2
Time of charging with the increasing in battery
Temperature
38
xii
LIST OF FIGURES
FIGURE NO.
TITLE
PAGE
1.1
NiCd charging rate versus temperature
4
2.1
40 pin PIC 16F877A
12
3.1
Flow chart the whole project
20
3.2
Power supply and charging circuit
22
3.3
Thermistor TTC103
23
3.4
Characteristic Curve
24
3.5
2x16 LCD Display
25
3.6
LCD display connection
26
3.7
Driver circuit
28
3.8
Developing PIC circuit
29
3.9
Methodology of Programming
31
3.10
Example of Hex files
32
3.11
Hardware and labeling
34
4.1
Charging voltage versus Time
37
4.2
Battery temperature versus Time
39
xiii
LIST OF APPENDICES
APPENDIX
TITLE
PAGE
A
PIC Programming
45
B
PIC 16F877A Data Sheet
48
C
High/Low Driver Data Sheet
54
D
Thermistor TTC103 Data Sheet
57
E
Voltage Regulator LM317 Data Sheet
59
F
Power MOSFET IRF540
61
G
Table of Price
63
H
Hardware of the Project
65
1
CHAPTER 1
INTRODUCTION
1.1
Overview
Nowadays electronic gadgets are widely use due to the growth of new
technology. Most electronic gadgets use dry cell as their main energy source; this is due
to its small size, efficiencies and recharge ability. Recharge the battery can save cost and
reduce the thrown of old battery which can effect the environment. Temperatures do
affect the battery since battery is electrochemical devices that convert chemical energy
into electrical energy. As full charge is reached the amount of energy used in the
endothermic reaction decrease and the amount dissipated in heat increase (making the
cell get hot).
Connecting a device creates a current and the electrons flow through the device
to the positive side. At the same time, an electrochemical reaction takes place inside the
batteries to replenish the electrons. The effect is a chemical process that creates
electrical energy. Once the battery nears a full charge, excess charge current becomes
heat. Small at first, the heat begins to accumulate in the mass of the battery side. As the
heat accumulates, temperature of the battery begins to rise. Current through the battery
begins to double for every degree C, thus more power is dissipated in the battery which
means more heat is generated, as a result more current flows which produce more heat.
2
The essence of good charging is to be able to detect when the reconstitution of
the active chemicals is complete and to stop the charging process before any damage is
done while at all times maintaining the cell temperature within its safe limits. Detecting
this cut off point and terminating the charge is critical in preserving battery life. In the
simplest of chargers this is when a predetermined upper voltage limit, often called the
termination voltage has been reached. This is particularly important with fast chargers
where the danger of overcharging is greater.
The charger has ability to turn of when the battery is fully charged, this is due to
voltage drop at resistor 10ohm. Its then drive the transistor PNP and finally energize the
12V relay to cut off the circuit. The charging voltage can be varied using 1K ohm
potentiometer to maximum voltage 6.67V. Here I use PIC 16F877A to read the
temperature from thermistor and display the temperature on LCD. In order to maintain
the battery’s temperature, 12V cooling fan is use. The cooling fan is set to start rotate
when the temperatures reach 31 degree Celsius.
3
1.2
Objectives
The main objective of the project is:
i.
To charge four units at 1.25V NiCd cell from no charge condition to full charge.
The charge is determined by connect the battery to the load such as 12V motor, if
the motor is not running or slow, then the battery is said to have low charge or no
charge as well and otherwise.
ii.
To display the temperature of the batteries being charge on the LCD.
iii.
To turn on the 12V cooling fan when temperature of the battery reach 31ºC and
above (the value can be adjusted due to ambient room temperature).
The important part of this project is to drive the 12V cooling fan when battery’s
temperatures reach 31 ºC. Here driver circuit is implemented in order to drive the
fan.
1.3
Scope of project
The scope of the project is to develop the power supply circuit that reduce the
240V AC to 9V AC and then convert to DC using bridge rectifier. Secondly is to
charging the 4 unit NiCd AA cells from no charge condition to full charge. And the third
part is to measure the temperature of the battery and display on LCD. The last part is to
drive the cooling fan when temperatures of the battery reach 31 ºC and above.
4
1.4
Problem Statement
This project is about developing the fast charging NiCd charger that boosts high
current into the battery. High current that enter into the battery reduce the charging time,
the charger only require 5 to 6 hours to completely charging from no charge to fully
charge. The temperature start increase rapidly when the cell is almost achieve full charge
as shown in Figure 1.1. Thus it is important for fast charging charger to maintain the
battery temperature within 10 degree C to 40 ºC, and the ideal temperature is 25 ºC for
optimal charging.
The main problem of fast charging is heat that produce in the battery due to
power dissipated. The increasing in heat effect the increasing of battery resistance, as the
result the charging process became less efficiency due to voltage drop before inserting
into the battery. It is important to maintain the battery temperature to make sure the fast
charging is affianced and less power or voltage loss.
Figure 1.1: NiCd charging rate versus temperature
5
1.5
Thesis Organization
This thesis consists of five chapters including this chapter. The contents of each
chapter are outlined as follows;
First chapter is the introduction of the thesis which contains the overview,
objectives, scopes and problem statements of the project. Chapter 2 contains the detail
description each part of the project. It will explain about the NiCd cells, charging circuit,
thermistor, PIC and driver circuit of the cooling fan. Chapter 3 includes the project
methodology. This will explain how the project is organized and the flow of the process
in completing this project.
Chapter 4 presents the expected result and analysis of the charging rate and
charging rate with the increasing in temperature. Finally the conclusion and
recommendation is presented in chapter 5. The conclusion part is to conclude the project
in detail and recommendation is the suggestion in order to upgrade the project so that it
can be more effective and can be commercialized.
6
CHAPTER 2
LITERATURE REVIEW
2.1
NiCd Cells
2.1.1
Introduction of NiCd cells
The nickel-cadmium battery (commonly abbreviated NiCd) is a type of
rechargeable battery using nickel oxide hydroxide and metallic cadmium as electrodes.
[1]
The abbreviation NiCad is a registered trademark of SAFT Corporation and
should not be used to refer generically to nickel-cadmium batteries, although this brandname is commonly used to describe all nickel-cadmium batteries. On the other hand, the
abbreviation NiCd is derived from the chemical symbols of nickel (Ni) and cadmium
(Cd), though it is not to be confused with a chemical formula. [1]
7
2.1.2
Advantages
The principal advantages of NiCd over other rechargeable types is lower weight
for a given quantity of stored energy, good charging efficiency, small variation in
terminal voltage during discharge, low internal resistance, and non-critical charging
conditions. They can be used in place of regular (lead-acid) batteries in most
applications. They have a much higher tolerance for extremes in heat and cold, whereas
standard lead-acid batteries suffer shorter life expectancy at higher temperatures and
reduced output capacity at lower temperatures. [1] [8]
2.1.3
Voltages
Nickel-cadmium cells have a nominal cell potential of 1.25 V. This is lower than
the 1.5 V of many popular primary cells, and consequently they are not appropriate as a
replacement in all applications. Unlike common primary cells, a NiCd cell's terminal
voltage only changes a little as it discharges. Because many electronic devices are
designed to work with primary cells that may discharge to as low as 0.90 to 1.0 V per
cell, the relatively steady 1.25 V of a NiCd is enough to allow operation. Some would
consider the near constant voltage a drawback as it makes it difficult to detect when the
battery charge is low. [1]
NiCd batteries used to replace nominally 9-V "transistor radio" batteries usually
only have six cells, for a terminal voltage of 7.2 volts. While most pocket radios will
operate satisfactorily at this voltage, some manufacturers such as Varta made 8.4 volt
batteries with seven cells, for more critical applications. [1]
8
2.1.4 Charging
NiCd batteries can charge at several different rates, depending on how the cell
was manufactured. The charge rate is measured based on the percentage of the amp-hour
capacity the battery is fed as a steady current over the duration of the charge. Regardless
of the charge speed, more energy must be supplied to the battery than its actual capacity,
to account for energy loss during charging, with faster charges being more efficient. For
example, the typical "overnight" charge, called a C/10 charge, is accomplished by
applying 10% of the batteries total capacity for a period of 14 hours; that is, a 100 mAh
battery takes 140 mAh of energy to charge at this rate. At the "fast charge" rate, done at
100% of the rated capacity, the battery holds roughly 80% of the charge, so a 100 mAh
battery takes 120 mAh of energy to charge (that is, approximately 1 hour and fifteen
minutes) The downside to faster charging is the higher risk of overcharging, which can
damage the battery. [1]
The safe temperature range for a NiCd battery in use is between −20 °C and
45 °C. During charging, the battery temperature typically stays low, around 0°C (the
charging reaction absorbs heat), but as the battery nears full charge the temperature will
rise to 45–50 °C. Some battery chargers detect this temperature increase to cut off
charging and prevent over-charging. [1]
When not under load or charge, a NiCd battery will self-discharge approximately
10% per month at 20 °C, ranging up to 20% per month at higher temperatures. It is
possible to perform a "trickle charge" at current levels just high enough to offset this
discharge rate; to keep a battery fully charged. However, if the battery is going to be
stored unused for a long period of time, it should be discharged down to at most 40% of
capacity (some manufacturers recommend fully discharging, or even short-circuiting),
and stored in a cool, dry environment. [1]
9
2.1.5 Charging Method
A NiCd battery requires a charger with a slightly different voltage charge level
than a lead-acid battery, especially if the NiCd has 11 or 12 cells. In addition, the
charger requires a more intelligent charge termination method if a fast charger is used.
Often NiCd battery packs have a thermal cut-off inside that feeds back to the charger
telling it to stop the charging once the battery has heated up and/or a voltage peaking
sensing circuit. At room temperature during normal charge conditions the cell voltage
increases from an initial 1.2 V to an end-point of about 1.45 V. The rate of rise increases
markedly as the cell approaches full charge. The end-point voltage decreases slightly
with increasing temperature. [1]
2.1.6
Overcharging
Overcharging must be considered in the design of most rechargeable batteries. In
the case of NiCds, there are two possible results of overcharging:

If the anode is overcharged, hydrogen gas is produced

If the cathode is overcharged, oxygen gas is produced.
For this reason, the anode is always designed for a higher capacity than the
cathode, to avoid releasing hydrogen gas. There is still the problem of eliminating
oxygen gas, to avoid rupture of the cell casing. NiCd cells are vented, with seals that fail
at high internal gas pressures. The sealing mechanism must allow gas to escape from
10
inside the cell, and seal again properly when the gas is expelled. This complex
mechanism, unnecessary in alkaline batteries, contributes to their higher cost.
NiCd cells dealt with in this article are of the sealed type (see also vented type).
Cells of this type consist of a pressure vessel that is supposed to contain any generation
of oxygen and hydrogen gasses until they can recombine back to water. Such generation
typically occurs during rapid charge and discharge and exceedingly at overcharge
condition. If the pressure exceeds the limit of the safety valve, water in the form of gas is
lost. Since the vessel is designed to contain an exact amount of electrolyte this loss will
rapidly affect the capacity of the cell and its ability to receive and deliver current. To
detect all conditions of overcharge demands great sophistication from the charging
circuit and a cheap charger will eventually damage even the best quality cells. [1]
2.2
Thermistor
2.2.1 Introduction
Thermistor is temperature sensing device base on resistance, which means is
there are any change in temperature then the resistance of the device will change. [6]
11
2.2.2 Advantages
The main advantage of thermistor is due its low cost compare to other
temperature sensor available on market today. It’s also easy to use, since it’s come with
2 pin connected and have no polarities. [6]
2.2.3 Disadvantages
Thermistor is temperature sensing that actually function as a switch in analog
circuit. It’s not suitable for measuring temperature since its variable in resistance,
compare to other temperature sensing which variable in voltage (analog) or output in
digital. [6]
2.3
PIC Microcontroller
PIC is a family of Harvard architecture microcontrollers made by Microchip
Technology, derived from the PIC1640 originally developed by General Instrument's
Microelectronics Division. The name PIC initially referred to "Programmable Interface
12
Controller”, but shortly thereafter was renamed "Programmable Intelligent Computer".
[2]
PICs are popular with developers due to their low cost, wide availability, large
user base, extensive collection of application notes, availability of low cost or free
development tools, and serial programming (and re-programming with flash memory)
capability. Figure 2.1 shows PIC 16F877A that has been use in the project. [2][5]
Figure 2.1: 40 pin PIC 16F877A
13
2.3.1 History
The original PIC was built to be used with General Instruments' new 16-bit CPU,
the CP1600. While generally a good CPU, the CP1600 had poor I/O performance, and
the 8-bit PIC was developed in 1975 to improve performance of the overall system by
offloading I/O tasks from the CPU. The PIC used simple microcode stored in ROM to
perform its tasks, and although the term wasn't used at the time. [2]
In 1985 General Instruments spun off their microelectronics division, and the
new ownership cancelled almost everything — which by this time was mostly out-ofdate. The PIC, however, was upgraded with EPROM to produce a programmable
channel controller, and today a huge variety of PICs are available with various on-board
peripherals (serial communication modules, UARTs, motor control kernels, etc.) and
program memory from 512 words to 64k words and more (a "word" is one assembly
language instruction, varying from 12, 14 or 16 bits depending on the specific PIC micro
family). [2]
Microchip Technology does not use PIC as an acronym in fact the brand name is
PICmicro. It is generally regarded that PIC stands for Peripheral Interface Controller,
although General Instruments' original acronym for the initial PIC1640 and PIC1650
devices was "Programmable Interface Controller".[2] The acronym was quickly replaced
with "Programmable Intelligent Computer"[2]