THERMOELECTRIC MOBILE CHARGER REPORT

Transcription

1 THERMOELECTRIC MOBILE CHARGER REPORT Prepared by: Harsha Sudanagunta 10BEE0149 Varshit Pasam 11BEE0039 Guided by: Prof.S.Meikandasivam SELECT

2 ABSTRACT A circuit was designed to generate and utilise electricity for use by mobile electronic equipments. This project will be based on thermoelectric devices that convert heat energy to electricity. During this, thermoelectric device will be tested in a variety of configurations with the goal of demonstrating a thermoelectric-powered mobile charging circuit. INTRODUCTION Our addiction to electricity has generated a concurrent addiction to fossil fuels. However, the reserves of fossil fuels will soon be depleted, since oil is a limited resource. Over the years, the cost of electricity has risen to unprecedented levels due the limited supply of oil and economic and political factors. Thus, renewable energy is a more attractive alternative to electricity generation, as it will also provide a cleaner environment for future generations. In the world today, there are many great solutions to renewable energy, but some are unfeasible. In this proposed project, a device will be created to introduce a way for humans to create renewable energy using thermoelectric devices. Renewable energy can be created by many methods; for example, solar energy, wind energy, hydro energy, nuclear energy, and many more. For each of these different forms of creating electricity, there are certain limitations. Solar energy is the most commonly form of renewable energy that is used in applications ranging from household power to spacecraft electrical systems. However, solar energy can only be created when there is sunlight, necessitating the use of alternate energy sources, or a method of storing energy for later use. Wind energy and hydro energy have their own limitations, making them insufficient for wider usage. Nuclear energy is used in applications such as power plants and military vehicles. Nuclear sources can supply adequate amounts of energy, but produces hazardous waste that is harmful to the environment. This project aims to provide a source of renewable energy that overcomes the limitations of current methods. Also, heat rejected from exhaust vents of Personal computers, Electric vents can be used to create a temperature difference across the thermoelectric module.

3 DESIGN AND FABRICATION A thermoelectric generator is a device that consists of a p-type and n-type semiconductors connected in series, shown in Figure, This structure can be used to convert heat energy to electricity by using a principle known as the Seebeck effect. When heat is applied to one surface of the thermoelectric generator, the electrons in the n-type semiconductor and the holes in the p- type semiconductor will move away from the heat source. This movement of electrons and holes gives rise to an electrical current. The direction of the current is opposite to the movement of the electrons, and in the same direction as the movement of the holes. By creating the appropriate electrical connections, the current of the thermoelectric generator flows in a closed loop through the p-type and n-type semiconductors and an external load. This pair of n-type and p-type semiconductors forms a thermocouple. A thermoelectric generator can consist of multiple thermocouples connected in series, which increases the voltage output, and in parallel to increase the current output. Performance Specifications of TEC Hot Side Temperature (ºC) 25ºC 50ºC Qmax (Watts) Delta Tmax (ºC) Imax (Amps) Vmax (Volts) Module Resistance (Ohms) Ceramic Material: Alumina (Al 2 O 3 ) Solder Construction: 138ºC, Bismuth Tin (BiSn)

4 up-to-date best thermoelectric materials: - Bi 2 Te 3 /Sb 2 Te 3, PbTe, Si-Ge NEW MATERIALS: Skutterudites, Heussler alloys, complex chalcogenides, oxides Graph of voltage and current, power as a function of temperature gradient The thermoelectric module was placed on a hotplate, while the cold side was left at room temperature. As the temperature of the hotplate increased, the voltage and current from the thermoelectric module increased as well. The measurement of voltage and current was done by using a multi-meter, with the probes placed at the positive and negative terminals of the thermoelectric module. The voltage and current measurements were recorded, but they did not match the specifications given by the datasheets. When observing the thermoelectric module, the cold side of the thermoelectric module was getting hot as the temperature of the hot plate increased. In addition, the voltage of the thermoelectric module was gradually decreasing over time, corresponding to the heating of the cold side of the module. In order to cool the cold side of the thermoelectric module, an ice cube was placed on the cold side of the thermoelectric module; The substrates hold the overall structure together mechanically and electrically insulate the individual elements from one another and from external mounting surfaces.

5 CIRCUIT DIAGRAM Circuit is constructed on a printed circuit board as per the given the circuit diagram and is fixed on to a wooden base. Thermoelectric module's Red wire is connected to blue wire of the circuit. Black wire of Thermoelectric module is connected to black wire of the circuit By maintaining Th=25 0 C,Delta T=50 0 C,a voltage of 10-12V is generated which is fed to the circuit, voltage can be regulated to 5V,the output(vout) is connected to a USB port

6 LM 317: It is an adjustable voltage regulator IC which means it provides Line Regulation (irrespective of the changes in the input voltage, the output voltage remains constant) and Load Regulation (irrespective of the changes in load the output voltage is fixed). We can adjust the output voltage by varying the resistance across the adjust pin. This is needed to have a fixed voltage across the battery (to limit the current and charge it at constant voltage). Directly connecting the Thermoelectric module to the mobile may even explode it due to the varying output from it. The voltage across R1 is maintained to be 1.25 V using an internal circuit. The Vout is also then obtained to be constant and given by: Vout = VR1*(1+R2/R1)+Iadj*R2. This Iadj is of the order of microa so can be neglected to have a regulated output voltage. RESULTS/ANALYSIS T.E.M was placed on a flame, while a beaker of ice was mounted on the top side of the T.E.M. The hot plate was set at different temperatures, to determine the voltage and current that was produced by this device. Since the flame didn t have precise temperature settings, a thermometer was used to determine the actual temperature produced by the flame. The precise temperature measurements were made by placing a thermometer in a beaker of water that was on a flame. In addition the thermometer was used to measure the temperature of the ice. The measurements of the temperature of the cold element and the hot element played an important role to determine the temperature gradient.

7 CONCLUSION Thermoelectric generation can be a suitable energy source in space, especially in situations where other power sources cannot operate. An alternative energy source is photovoltaics, which actually have a much higher efficiency (up to approximately 40%, as compared to approximately 5% for a thermoelectric generator). In addition, thermoelectric generators are relatively inexpensive, easy to handle, and robust, as they are solid-state devices with no moving parts. In conclusion, these thermoelectric generators can be useful in electrical systems, including satellites, robots, and automobiles. Thermoelectric modules offer many advantages including: No moving parts Small and lightweight Maintenance-free Acoustically silent and electrically quiet Heating and cooling with the same module (including temperature cycling) Wide operating temperature range Highly precise temperature control (to within 0.1 C) Operation in any orientation, zero gravity and high G- levels Environmentally friendly Sub-ambient cooling Cooling to very low temperatures (-80 C) Besides low efficiency, two general problems exist in such devices: high output resistance and adverse thermal characteristics. REFERENCES Thermoelectric effect. Wikipedia. Thermoelectric effect. < > "Photovoltaic Panel-Gun Barrel Thermoelectric Generator Charging System" < _Harris.pdf> Thermoelectric Module Manufacturer exporting direct from China. Alibaba. Thermoelectric Module. < /Thermoelectric_Module.html>. "TEC datasheet" <