SOLAR BASED MOBILE CHARGER PROJECT REFERENCE NO. : 37S1422 COLLEGE : ST. JOSEPH ENGINEERING COLLEGE, MANGALORE. BRANCH : ELECTRONICS AND COMMUNICATION GUIDE : SHAMA B. N. STUDENTS : ASHLESH KUMAR AMRA FATHIMA AMLINE JOSNA DSOUZA YOGISH V HEBBAR Introduction: In today s environment conscious world, a lot of interest is being taken in alternate forms of energy. Solar power is a renewable source of energy, which has become increasingly popular in modern days. Today 80% of the energy we use comes from fossil fuels and about 1% comes from solar energy. It is estimated that the world s oil reserves will last for 30 to 40 years, whereas solar energy is forever. Solar energy has two big advantages over fossil fuels. The first is in the fact that it is renewable; it is never going to run out. The second is its effect on the environment. Burning of fossil fuels introduces many harmful pollutants into the atmosphere and contributes to global warming and acid rain. Solar cell directly converts solar energy into electricity. The solar cells that are connected together make up the solar panel. This can last up-to several decades without replacement. However, there is a drawback of solar power: energy can be produced only in the presence of sunlight. To overcome this, the solar panels are coupled with the rechargeable batteries, which can store excess power generated and provide energy in the absence of sunlight. Solar energy has advantages over other renewable energy sources including wind and water power: solar power is generated using solar panels, which do not require any major mechanical parts, such as wind turbines. These mechanical parts can breakdown and cause maintenance issues and can also be quite noisy. Both of these issues are virtually non-existent with solar panels. This project aims at harvesting solar energy and storing it in a rechargeable battery. Using this battery various low-voltage device can be charged. Also, the charge in the battery is displayed on an LCD through a micro-controller. 1
Objectives: Solar energy as energy source. Rechargeable battery as storage device. Multi-voltage outputs. Charging of various low-voltage devices. Battery charge analyzer. Display of critical conditions of the battery. Methodology: Block Diagram: Figure 1: System Block Diagram The block diagram of solar mobile charger consists of solar panel with control unit, fixed voltage regulators, rechargeable battery, ADC, Schmitt trigger, micro-controller and an LCD. The solar panel of 12V, 10W is used, the output of which varies based on the intensity of incident light. This output is regulated through a control unit and is stored in a battery. This battery produces an output of 12V which can be used directly to charge the load. A 9V fixed output can be obtained by regulating the voltage from battery using an L7809 voltage regulator and can be used to charge a 9V load. The battery can be regulated further to obtain 2
a 5V fixed output, using L7805 and charge a 5V load. The 5V output, so obtained, is also used to power-up the micro-controller, ADC, Schmitt trigger and the LCD. The Schmitt trigger is used to trigger the ADC0808 which converts the analog voltage across the battery terminals into digital. Micro-controller AT89S51 is used to display this charge on the LCD JHD0161. The analysis of charge present in the battery is performed by scaling down the output of rechargeable battery (12V) to 4.3V. The LCD displays the percentage of charge in the battery, and critical conditions in the battery (if the battery is full, low, etc.) Circuit Diagram: Figure 2: Circuit Diagram The solar panel is used to charge the rechargeable battery. This rechargeable battery is interfaced with the 78L05 and 78L09 voltage regulators to charge 5V, 9V, 12V loads. The 5V output is also used to power-up the analyzer circuit. Analyzer circuit consists of Schmitt trigger, ADC, Micro-controller and LCD. The Schmitt trigger CD4093 acts as the timer to ADC, generating a clock of 550kHz frequency. The ADC analyzes the voltage across the battery terminals and converts it into digital form. The micro-controller displays the charge in the battery on the LCD. It also displays whether the battery is fully charged and if the battery charge is below 20%, stating low battery. The Schmitt trigger frequency can be varied by varying the external resistor, capacitor values. The digitized output from the ADC (AD 0 -AD 7 ) 3
transfers the voltage across the battery terminals in digital form to the port 1 of the microcontroller. The voltage-divider circuit scales-down the battery terminal voltage to a maximum of 5V. Based on this voltage, the micro-controller analyzes the charge in the battery and displays this on the LCD through port 2. The flowchart to analyze the charge in the rechargeable battery is shown in the figure 3. Result: Figure 3: Flowchart to analyze the charge in the battery The table 1 indicates the time taken to fully charge the battery using the solar panel at different times on a day in summer. 4
Table 1: Time required charging a battery Around 7am (morning) Around 10am (morning) Around 1pm (noon) Around 5pm (evening) 2 hours 1 hours 15 minutes 35 minutes 1 hour 35 minutes The table 2 shows the voltage across the solar panel at various times on a day. The following readings were taken on 1 st May 2014(day was cloudy). Table 2: Voltage across solar panel Time Max. Voltage (in V) Time Max. Voltage (in V) 6am 2 1pm 14 7am 3.5 2pm 14 8am 6 3pm 10 9am 9 4pm 8.5 10am 10 5pm 6 11am 12 6pm 3 12pm 13 7pm 1.5 Figure 4: Hardware implementation of the device 5
Figure 5: Charge state displayed on LCD Applications: To charge mobile phone and camera (digital as well as CC cameras). MP3, CD and MD players can be charged. This device can also be used to charge batteries of portable DVD, smart card readers, etc. To charge laptop, I-pods, tablets, blue-tooth devices etc. To power 2W bulbs in hut, bed-lamps, low-watt lights, etc. Conclusion: Solar act as good power supplies in bright sunlight. The only problem is the unregulated voltage due to the variation in intensity of light. Voltage regulator is used to solve this problem by regulating the output voltage. The charge so obtained is stored in the battery and is given to the respective loads. The charge present in this battery is analyzed and displayed on an LCD using a micro-controller. Future scope: Solar energy can only be harnessed when it is daytime and sunny. To overcome this, solar panels can be coupled with back-up battery which can store the excess power generated during the day and use it to provide energy to system in the absence of sunlight. The Lead-acid battery used in the design is large in size and heavy in weight which makes the device non-portable. Hence a battery of pocket size and optimal weight may be designed to make the device portable. 6
The large size of the solar panel makes the device bulky and non-portable. The solar panel should be fabricated to cover the entire device, which can effectively reduce the size of the entire device. 7