A Battery is an electric cell or a device that converts chemical energy into electricity. It consists of two or more cells connected in series or parallel, but the term is also used for single cells. All cells consist of a liquid, paste, or solid electrolyte and a positive electrode, and a negative electrode. The electrolyte is an ionic conductor;
one of the electrodes will react, producing electrons, while the other will accept electrons. When the electrodes are connected to a device to be powered, called a load, an electrical current flows.
Batteries in which the chemicals cannot be reconstituted into their original form once the energy has been converted (that is, batteries that have been discharged) are called primary cells or voltaic cells. Batteries in which the chemicals can be reconstituted by passing an electric current through them in the direction opposite that of normal cell operation are called secondary cells, rechargeable cells, storage cells, or accumulators. The storage battery, or secondary cell, which can be recharged by reversing the chemical reaction, was invented in 1859 by the French physicist Gaston Planté.
The lead-acid battery, which consists of three or six cells connected in series, is used in automobiles, trucks, aircraft, and other vehicles. Its chief advantage is that it
This publication is a scholastic property of Morakinyo A.J, Amusan O.S, Sekoni, et al.
©2011 can deliver a strong current of electricity for starting an engine; however, it runs down quickly. The electrolyte is a dilute solution of sulphuric acid; the negative electrode consists of lead, and the positive electrode of lead dioxide. In operation, the negative lead electrode dissociates into free electrons and positive lead ions. The electrons travel through the external electric circuit, and the positive lead ions combine with the sulphate ions in the electrolyte to form lead sulphate. When the electrons re-enter the cell at the positive lead-dioxide electrode, another chemical reaction occurs. The lead dioxide combines with the hydrogen ions in the electrolyte and with the returning electrons to form water, releasing lead ions in the electrolyte to form additional lead sulphate.
A lead-acid storage cell runs down as the sulphuric acid gradually is converted into water and the electrodes are converted into lead sulphate. When the cell is being recharged, the chemical reactions described above are reversed until the chemicals have been restored to their original condition. A lead-acid battery has a useful life of about four years. But, it is a good practice to utilize along with the battery, a suitable charge controller, as this will help the battery perform better and last longer.
According to H.P. Garg and J. Prakash, overcharging of some batteries results in loss of electrolyte, corrosion, plate growth and loss of active material from the plates, causing reduction in battery life. Also, repeated failure to reach full charge leads to stratification of electrolyte. Thus, there is a need of charge regulators/controllers to optimize the battery life.
This publication is a scholastic property of Morakinyo A.J, Amusan O.S, Sekoni, et al.
©2011
CHAPTER THREE
DESIGN & CONSTRUCTION
3.1 BASIC DESIGN
The design is such that the solar panel will be installed on the galvanized pole considering some specifications like angle of tilt and direction of sunlight. The fabricated pole will be bolted on a flat slab and its uprightness will be checked using a plum. The 12V dc battery that will power the LED bulbs will be connected to the solar panel via the charge controller for charging purpose. The pole will be constructed such that it will have two wings with each wing carrying one LED bulb or lamp. The automatic switching of the lamp (ON or OFF) will be performed by the light sensor circuit which consists of the light dependent resistor (LDR), relay, op-amp, transistor and some other electronic components.
Fig. 3.1 Block Diagram of a Solar-powered Street Light (Automatic)
The solar panel is tilted at an angle in the range of 15°≤x≤30° facing the geographical south. This is because Nigeria (wherein this project is being executed) is situated in the geographical north of the globe. The sun rises at the east and sets at the west and illumination is directed towards the geographical north. After erections have been made on the erected pole of about 18ft, the panel would be tightened up using bolts and nuts. The photovoltaic cells on the solar panel would generate voltage when it is well illuminated by light.
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©2011 3.2 CHARGE CONTROLLER
The charge controller serves as an interface between the current generated by the module and the battery charging during the day. The battery is prevented from over-current or over-charging by the charge controller. The charge controller is an electronic circuit comprising an operational amplifier (connected in comparator mode), an electronic switch (transistor) and an electromechanical switch (relay). The block diagram of a charge controller is shown on figure below:
Fig 3.2 Block Diagram of Charge Controller Unit
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©2011 Fig 3.3 Circuit Diagram of a Charge Controller
When
When VCC = 14V, VP = 7V (which is less than the reference voltage). Hence, a variable resistor will be ideal for R2.
Choosing VP = 9V for us to have a high output.
R1 = 1KΩ, VCC = 14V, But R2 must be obtained:
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©2011 14R2 = 9 + 9R2
5R2 = 9
Preferred value, R2 = 5KΩ variable.
The comparator (LM 324) IC compares the non-inverting input voltage VP and the non-inverting input voltage VN. There is usually a high output from the OP-AMP if VP>VN which will switch on the transistor that will trigger the relay once the +VCC on the battery rises to 14V in order to cut off the battery from charging throughout the photovoltaic supply. A freewheeling diode is connected across the coil terminals of the relay to protect the components from back emf from the inductive coil.
3.3 CHOOSING SOLAR PANEL (RATINGS)
Using four of the 5W LED bulbs amounts to 20W of electrical power being dissipated at 12V rating, PSH = 5hrs (time of maximum illumination)
Current consumption of the 20W load = Power/Voltage = 20/12. Hence, IL = 1.67A.
Ampere hour needed per day (i.e. from 7p.m till 7a.m (12hours)) becomes:
(1.67 x 12) this yields approximately 20Ah. While current needed from the solar panel is:
Hence, a panel that could supply a current of 4A is needed. Preferred value is 4.2A per 50W panel.
3.4 PARAMETERS FOR CHOOSING A BATTERY
Ampere-hour of the battery needed = Amp-hr needed per day x number of days of autonomy /Depth of discharge.
Autonomy number is the number of days that could be cloudy that you want the system to work effectively. (e.g. 2days)
This publication is a scholastic property of Morakinyo A.J, Amusan O.S, Sekoni, et al.
©2011 Depth of discharge (D.O.D.) of a battery is a measure of how much energy has been taken away from a battery. With the lead-acid dry cell battery in use for this project, a discharge of 50% or 0.5 is allowed for it without damage caused to it. Therefore,
:
Preferred value for battery is 60Ah to allow for losses.
3.5 DARK OPERATED SENSOR AND SWITCHING CIRCUIT
The light dependent resistor (LDR) senses the dark and daytime and responds correspondingly to changes in the weather by causing the resistance of the resistor to vary from about 1KΩ to 100KΩ and vice versa. The incorporated sensor and switching circuit is shown in the next page:
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©2011
N
V
V
D T
3 2
4
11 1
.
© Amusan Olusola 2011© Amusan Olusola 2011
Fig. 3.4 Sensor and Switching Circuit
This change in resistance causes a change in the voltage levels or the value of the non-inverting input (VP). Assuming that VN is being regulated constantly by the voltage divider between R1 and R2, we assume that R1 = R2, which in turn equals 10KΩ,
Then,
When LDR is at 1KΩ, (daytime);
Here, it is seen that VP < VN, implying that there is low output.
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©2011 When the LDR (Rλ) is at 100KΩ, (Dark time),
Then VP is
Here, VP>VN which in turn fulfills the condition for high output of the comparator. The high output of the comparator would switch on the transistor and it conducts to trigger the relay which will switch on the LED bulbs at the dark time. A freewheeling diode is connected across the coil terminals of the relay for protection against back e.m.f.
The variable 10KΩ resistor is used to tune up the sensitivity of the dark operated sensor. The 1KΩ resistor connected in series with the LED indicator for the output serves as a current limiter for the light emitting diode. The maximum current of the LED is 10mA which is IF. The output voltage VCC is also known as the LED operating voltage (VLED). This has a value of 12V.
.
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will be installed requires a suitable mechanical engineering design. Mechanical design means the design of things and systems of a mechanical nature. For the most part, mechanical design utilizes mathematics, the material science and the engineering mechanics science (Charles R. Mischke, 2002). This comprises a galvanized steel column, mild steel solar tray guide, base plate, light brace support, battery and circuit container as well as a variety of suitable fasteners.
The two main types of metallic materials utilized are discussed in the following paragraphs.
Galvanized Steel
According to William F. Hosford (2005), galvanized means zinc plated.
Because zinc is anodic to iron, galvanizing protects the steel from corrosion.
Galvanized steel is a form of steel that has gone through a chemical process to keep it from corroding. During the process, the steel gets coated in layers of zinc to prevent rust, since zinc is resistant to rust. Galvanized steel is an essential fabrication component for outdoor applications as well as industrial marine use. The major method of preventing steel from corrosion is by alloying it with another metal such as zinc. The chemical reactions between the two metals cause a bonding to occur. This action does not make zinc a paint or coat.
Instead, it becomes part of it on a permanent basis. Zinc protects the steel by
acting as a sacrificial layer. As such, if rust occurs on the surface of galvanized
steel, the zinc part of it gets corroded first, and this prevents the rust from
getting to the pure steel.
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©2011
Galvanization process is termed hot dip galvanization. It is the process of coating iron, steel or aluminium with a thin layer of zinc, by passing the metal through a molten bath of zinc at a temperature of around 460˚C. The galvanic process was discovered by Luigi Galvani in the 1700s when he invented the galvanic cell. Galvanization is the name given to the electrochemical processes in his honour. This however should not be confused with galvanizing steel, because it is not an electrochemical process, though the result remains the same.
Steel in galvanized form can be found everywhere as it has wide applications. An advantage of this form of steel is its effectiveness. And above all, it can be recycled and re-used multiple times. Galvanized steel is very practicable in applications where this is high proximity to rust, and rust resistance is required. Galvanized steel is also suitable for high temperature applications of up to 200˚C. The use of galvanized steel at temperatures above this will result in peeling of the zinc at inter-metallic layer. Hot dip galvanized steel can be referred to as galvanized iron. It is used in heating and cooling duct systems in building.
Mild Steel
Also referred to as low carbon steel, mild steel is weldable and hard. It is malleable when heated, and as such can be forged. These properties are due to the presence of minute quantity of carbon content for hardening. It has a low content of carbon, up to (0.3%), and is neither extremely brittle nor ductile. It is used where large amount of steel has to be formed such as structural steel.
Other advantages of using mild steel include relative cheapness, availability of wide variety with different properties, high degree of stiffness and magnetic property.
Mild steel also has wide applications, as it is the most common form of
steel. It has got a relatively low price while it has properties that are acceptable
for many useful applications. Carbon steels that have about 0.3% require
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©2011
special precautions. Relative to stainless steel, there are fewer problems associated when welding mild steel. It has poor corrosion resistance, implying that it rusts easily. Hence, it should not be used in corrosive environment unless a provision for protective coating is made.
4.2 WELDING
It is a process of permanently joining two or more metal parts by melting both materials. Welding may be considered to be a fabrication technique. In welding, two or more parts are joined to form a single piece when one-part fabrication is expensive or inconvenient (William D. Callister, 1997).
The molten materials cool quickly and the two metals are permanently bonded.
Higher content or alloy steels tend to form hard welds that are brittle and could crack. This unsuitable tendency can be reduced by tempering. When low carbon steel is used, the surface-cleaning process which is becomes necessary when aluminium is used can be easily avoided, preventing further cost.
Materials that are similar in composition cannot be welded by spot welding method due to different melting properties and terminal conductivities. Steel that is plated can be assumed to take the characteristics of its coating. Nickel and chrome plate steels are relatively easy to weld by spot welding, whereas aluminium, zinc and tin need special preparation to be able to weld them.
Arc welding
This is a type of welding that uses a welding power supply to create an electric arc between an electrode and the base material, thereby melting the metal at the welding point. They use either direct current or alternating current consumable or non-consumable electrodes. The welding region is sometimes protected by some type of inert gas known as a shielding gas. This method of welding is widely used because of its low capital and running cost.
Welding of Galvanized Steel
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©2011
The welding of galvanized steel is done in the same way as the welding of base steel of the same composition. The difference between welding galvanized steel and uncoated steel is a result of low vaporization temperature of the zinc coating. The successful welding of galvanized steel is so widely accepted that there is little mechanical property that compares uncoated and galvanized weld. Weld toughness, porosity control, corrosion resistance, etc are much more complex that the strength of the weld.
4.3 SCREWING
Screwing is another method of joining metals. It consists of proper cleaning of the parts to be joined, and then using the appropriate joining pieces.
They are made of iron, brass, bronze or steel and have heads of various shapes, half-round heads, counter sunk heads, cheese heads, half round and counter length under head. In screwing work together, the part that takes the head of the screw has a clearing hole in it, while the other part has to have a tapping hole, and this is known as the core diameter. This enables the work to be drawn tightly together.
4.4 INSTALLATION
The automatic solar-powered street light is installed with a twin arm
lighting kit to operate in a dusk-to-dawn operation mode using an automatic
ON/OFF feature. The lighting kit does not utilize an inverter circuit but instead,
four 15Watt D.C. bulbs powered by D.C. supply from the battery are
employed.
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©2011
Installation of Solar Panel
Attach the solar panel tray guide or carrier upon the pole and slightly fasten its bolts and nuts. Fix the solar panel into the tray guide and tighten the appropriate screws effectively. Connect the 6mm cables from the panel terminals to the battery and also, from the battery to the electronic circuit unit.
Ensure that the standard polarities are observed i.e. black for negative (labelled –ve) and red for positive (labelled +ve). Adjust the solar panel’s direction and angle to obtain optimal performance, and fasten the bolts and nuts tightly.
Installation/Erection of Pole
An anti-skid unloaded metal pole having a square base is erected on a concreted square-shaped foundation. This base of the pole then fastened to the foundation by means of rag bolts. Consequently, the pole is made to stand uprightly.
Installation of the Lighting Kits & the Battery
Carefully secure the lighting kits into the lamp holders and fix the luminaries. Then connect the wires to the controller as shown in the associated wiring diagram of this project. Also, put the battery in the box attached to the erected pole, ensuring appropriate connection of cables unto it with battery clips.
Installation of the Charge Controller of the Automatic Switch
Since circuitry of this design incorporates both a charge controller unit
and a dark-operated sensor switch together as a kit, both units are installed on
the same electronic board and planted in the same enclosure together with the
battery. The battery, lighting lamps and the solar panel are connected
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©2011
appropriately to the charge controller/automatic switch as shown in the block wiring diagram as shown below.
SOLAR PANEL
4.2 Wiring Block Diagram of Automatic Solar-powered Street Light
4.5 TESTING
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©2011
After the installation process has been completed, an act of testing and if necessary, a troubleshooting session must be executed. Testing is the act of examining of the normal working operation, seeking to know the characteristics of the equipment and noting where appropriate changes can be made. On the other hand, troubleshooting is the art of isolating problem areas and using a variety of techniques and experience to solve it. These are done to ensure that the fabricated lightning equipment is in optimal working condition.
If any performance deviation is observed, the operation of the equipment must be troubleshooted in order to isolate the problem and fix the fault.
At night, the streetlight operated by itself, switching on the luminaries and by dusk, it switched off the lamps by itself. Therefore, the characteristics of the equipment were normal and there is no need for further changes. This project has been tested ok.
4.6 OBSERVATIONS
The following observations were made:
•
To enhance the sensitivity of the LDR and hence, improve the performance of the streetlight, the potentiometer was removed from inside the circuitry’s container and be put on the outside the casing.
•