This paper was presented on 3rd International Conference on Advanced in Computing and Emerging E-

Learning Technologies ( ICAC2ET 2013 ) – Singapore on November 6 – 7, 2013

Self sufficient continuous charging module for mobile phones Dinesh S Electronics and Communication , Sri Venkateswara College of Engineering Chennai, India [email protected] Ashwin M Electronics and Communication , Sri Venkateswara College of Engineering Chennai, India [email protected] Barath Kumar R Electronics and Communication , Sri Venkateswara College of Engineering Chennai, India [email protected] Fayyaz Ali baig .I Electronics and Communication, Sri Venkateswara College of Engineering Chennai, India [email protected] Abstract : With the Smartphone technology breaking boundaries as the features advance, there is an ever increasing need to meet the extensive usage of a normal user and to optimize the battery usage. It is undesirable for any person using a Smartphone to charge the battery at periodic intervals or when the person is moving or travelling. Currently separate portable batteries are extensively used to charge while travelling. This paper aims to utilise the available sources of energy in the vicinity of a mobile phone to recharge the batteries dynamically. This increases the longevity of its operation without charging. Our first method makes use of excessive heat generated by the human body. Thermocouples working on Peltier effect can effectively generate current when the human hand or any other portion of the body comes in contact with the module and creates a temperature difference. The potential generated can be used to charge the battery after necessary amplification. Our second method involves affixing solar cells to support the charging using thermocouples. Solar cells provide the additional current required to meet the Smartphone’s current requirement. This paper also makes an attempt to explore the feasibility of using a Piezo-electric method of charge generation by using crystal mounted on an elastic surface. This can be utilised when a person moves around with his phone in his pocket. All the above methods are to be mounted on a dedicated back plate for facilitating easier installation thereby making it suitable for use on a variety of handsets. Keywords: Piezo-electric crystal, Thermoelectric module, Solar cell, Peltier Effect, Piezo electric effect, Reverse piezo electric effect I. INTRODUCTION The advancements in smart phone industry such as larger screen and higher clock speed for mobile processors has led to extensive need for better battery storage capacities. Thus there is a need for replacing power hungry circuits with circuits that are more efficient. However this method compromises performance. Thus manufacturers have resorted to higher capacity batteries which provide the necessary battery life required for an average user. With the

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This paper was presented on 3rd International Conference on Advanced in Computing and Emerging E-

Learning Technologies ( ICAC2ET 2013 ) – Singapore on November 6 – 7, 2013

advancements in mobile technology smart phones perform a variety of functions ranging from basic ones such as calling, messaging to advanced multimedia activities such as video streaming, browsing, and all internet oriented applications that require constant internet connectivity to pull up data packets at predefined periods. Hence it is impossible for any manufacturer to restrict or confine the end user and impose restrictions on usage of the smart phone. Due to these reasons portable chargers have gained popularity and are an inevitable device associated with smart phones. The disadvantages associated with portable chargers are 

Their bulky nature makes them a separate and troublesome gadget to carry around.



Most portable chargers require constant charging and the charge duration is long.



Portable chargers when left idle are prone to discharge or permanent loss in battery capacity.

Hence there is a need for a novel method to recharge the in-built batteries in smart phones on-the-go without the need to have backup batteries. In the following sections we explore the advantages and disadvantages of the existing methods and describe a new module capable of charging which effectively uses the Peltier module and also certain features of the available methods. II. EXISTING SOLAR CHARGING METHODS Present day solar charging methods use photovoltaic cells that operate on the principle of photoelectric effect which converts incident light into electricity. These solar cells are affixed either on the back plate of the phone or are available as separate portable charging modules. Solar cells are capable of providing energy from both indoor and outdoor sources but the efficiency of the solar cells drop down drastically in shady areas with little or no light. Currently solar cells have been employed in many gadgets like wrist watches, wireless sensors and so on. Transparent solar cells have also been used over LCD screens in mobile phones to harvest solar energy. The key features of using solar cells are as follows. 

Solar energy is a renewable energy source and is available in plenty. Solar cells are efficient and are capable of delivering enough voltage and current to charge a battery.



Solar cells can be used to derive energy from both external and internal light sources.

The drawbacks of using this method are: 

The voltage and current delivered by a solar cell is dependent on the quality of material used and the size the cell. Hence for pragmatic implementation, the area of the solar cell required is larger.



The power output of a solar cell drops exponentially when there is an absence of sunlight and is almost zero during the night. Furthermore the efficiency is drastically affected under cloudy conditions.

It is impossible to predict when a smart phone will run out of juice and thus solar cells can only be used as a supplementary energy source but cannot be used separately for recharging purposes. III. PIEZO ELECTRIC CHARGERS

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Piezo-electric chargers consist of a piezo electric crystal mounted on a metal plate or an elastic band and this is used in tandem with an amplifier circuit. They work on the principle of reverse piezo electric effect that when a mechanical force is applied on the surface of the piezo electric crystal, the variation in length of the crystal along its axes produces a current which can be utilised to charge a battery. The mechanical force that is applied to make the crystal bend can be stress resulting from pressing the crystal when a user handles the phone or the stress that is produced when a user walks around with the smart phone in the pocket. The above methods can be realized by using a piezo electric crystal employed on the same back plate attached to the phone as in the previous case. The crystal is attached in such a way that the the axes are expanded up to a threshold and any minute movement is capable of producing the necessary charge. The formula that governs the current produced is known as straincharge equation which is expressed using the formulae given below. D=εE

(1)

Where, D is the electric charge density displacement (electric displacement) , ε is permittivity is electric field strength. Hooke’s law is given by S=sT

(2)

Where, S is strain, s is compliance, T is stress. These may be combined into so-called coupled equations, of which the strain-charge form is: {S}=[sE]{T}+[d]{E}

(3)

{D}=[dt]{T}+[εT]{E}

(4)

Thus the electricity generated by a crystal is dependent on the following factors. Permittivity(ε) of the material used for the construction of the piezo-electric crystal. 

Strain(S) applied on the crystal surface.



Dimensions of the crystal which is based on constructional specifications.

The above method has its own advantages and disadvantages: 

Autonomous from factors such as day-night, indoor-outdoor conditions and is purely dependent on stress or force applied.



Voltage generated from a piezo electric crystal depends on the constructional specifications and also space availability. Hence the output is crippled due to these factors.



Piezo electric crystals are very fragile. Hence if the construction is not proper then the crystal is vulnerable to damage from external disturbances.

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

The voltage and current delivered by a solar cell is dependent on the quality of material used and the size the cell. Hence for pragmatic implementation, the area of the solar cell required is larger.



The power output of a solar cell drops exponentially when there is an absence of sunlight and is almost zero during the night. Furthermore the efficiency is drastically affected under cloudy conditions.

It is hence evident from the above points that this method cannot be employed alone and hence can be used as an auxiliary source.

IV.

PROPOSED THERMAL ENERGY CHARGING A thermal energy charger consists of a Peltier module or a thermoelectric module that operates on the principle of

Peltier effect which is a corollary of the Seebeck effect. According to Seebeck effect when a potential is applied to a thermocouple then it produces a temperature difference across its surfaces. According to Peltier effect when there exists a temperature difference between two ends of a thermocouple, a potential is generated. The potential that is generated can be amplified using a suitable amplifier circuit that can cater to the needs of battery charging. This opens up a possibility to utilize the excess heat generated from the human body. Thermoelectric modules can thus be mounted on special back plates for smart phones. Whenever the user’s hand comes in contact with the region of the back plate where the module is affixed, heat energy gets transferred to the one side of the module. Since the other side is insulated a temperature difference is created which constitutes an electric current which in turn can be utilized for charging purposes. The advantages of using thermoelectric modules are bulleted below: •

Thermoelectric modules are compact and are capable of producing considerable voltage/ current levels. Thus their size to output power ratio is attractive.

•

Minute temperature differences can be exploited and utilized.

•

Rigid, resilient and durable nature of these modules makes them ideal for long-term usage even under harsh environment conditions.

Thrives on temperature differences to produce current. Since the outer surface of the module is exposed to air, there is a high probability that the air outside may be hot or cold. Thus there is a high probability that a temperature difference will exist continuously thereby assuring a continuous potential difference and hence can effectively charge the in-built battery even without the knowledge of the user or his need to constantly touch the back plate of the phone. However there are disadvantages associated with using this method. •

The current/voltage generated is dependent on the magnitude of temperature difference. For lower temperature differences the output power is low and hence cannot be employed separately.

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•

Temperature differences generate a potential whose polarity changes if the hot and cold sides are interchanged. Hence it is necessary that the amplifier design should accommodate these difficulties.

V.

CHARACTERISTICS OF THERMOELECTRIC MODULE The thermoelectric module is primarily manufactured to be used as cooling equipment in computers. These

modules are compact and can be effectively used in the back plate of the proposed method. One of such modules that are available is as shown in Fig 1.

Fig.1:Thermocouple Peltier module The characteristics of the thermoelectric module are as follows: •

The module has proportional variation in temperature to the current applied to its terminals (i.e) depending on the current applied to its terminals, one of the plates is heated up and the other is cooled.

•

The converse of this effect is also true, when either of the plates is heated or cooled a potential difference is generated across the two terminals and also a current is produced.

•

The current and voltage levels are dependent on the temperature difference applied to the plates which is denoted as ΔT.The variation of the voltage with respect to temperature difference is as shown in the Fig.2

Fig 2.Characteristics of Peltier module As shown in Fig 2, when the temperature difference increases the voltage levels and the corresponding current also gradually increases. The voltage levels saturate after a certain temperature difference. VI.

IMPLEMENTATION OF THE PROPOSED METHOD

The implementation of the self sufficient charging module can be carried out using the components such as the Peltier module, Solar cells and the Piezo electric crystal with the help of some peripheral circuitry.

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Fig 3.Block diagram of the proposed charging method The fig 3 shows the proposed method of implementing the self-sustained charging technique which will be elucidated below. A solar cell of required size and shape is affixed to the special charging plate(back plate). The solar cell will generate a potential difference between its terminals whenever light falls on it. Thus by exposing the back plate to sunlight, a potential can be generated. The output of the solar cell is coupled to a Summer and a dual polarity amplifier through a protection circuit. The purpose of the protection circuit is to prevent reverse current from entering the solar cell to avoid the damaging it. A reverse current protection circuit may be a simple isolator or a suitable diode. Similarly the output of the Peltier module and the piezo-electric module are coupled to the summer and dual polarity amplifier through a protection circuit. The Peltier module will generate an emf whenever a change in potential exists between its two ends or junctions. The piezo electric module will generate an emf when pressure is applied to it. The necessity of the summer is that it is not possible to attain sufficient emf when these modules are used in standalone or solitary configurations. Hence the outputs of all these modules are combined to efficiently utilise and charge the battery. Furthermore the output levels of the solar cell will drop under overcast conditions. Hence in these situations the Peltier module and piezo-electric module may help improve the total emf compensating for the drop in solar cell output level. A normal amplifier may not suffice in this method because the potential generated by the Peltier module may be reversed if the hot and cold surfaces are interchanged. Hence there is a need for use of a dual polarity amplifier that will amplify both polarities when required. This Peltier module network can be used as a backup network while the other two can be used as the main network for charging the phone battery. The final output of the amplifier is fed to a voltage regulator circuit that limits the maximum output of the circuit according to the battery voltage and current threshold levels. (Ideally 5V, 1.2A). This output of this regulator is fed to the phone battery. An illustration of the back plate is shown in the fig 4 below.

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Fig 4.Illustration of charging back plate VII. CONCLUSION The smart phone world is improving at a rapid rate and hence with increased number of features, the battery lifetime requirements have increased at an alarming rate. Hence this self sufficient module will improve battery life and provide prolonged usage times without charging the mobile phone. The method uses three major components which are solar cells,Piezo electric crystal and Peltier module which when compiled together in the back plate will produce a combined potential sufficient to sustain a healthy usage time for the smart phones .The mass manufacture of this setup would reduce the cost and make it an affordable gadget associated with smart phones in the near future.

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