Design and Implementation of a Microcontroller based 12V-7A/10A Smart Solar Battery Charge Controller

Sabbir Ahmed1 Abu Bakkar Siddik2 Sheik Md. Kazi Nazrul Islam 3

Abstract— In this article, an upgraded battery charging system is introduced. The system has been upgraded using microcontroller, which can store charge more effectively and intelligently than the older ones in an automated systems. Here, for the purpose of the project a microcontroller PIC12F675 is used, which is programmed with the help of Proteus Arrays and code vision AVR. The circuit can operate at a maximum current of 22A with power MOSFET IRF540 whether a very low rated current is consumed at home appliances. A solar panel is used as the primary power source. A DC-DC converter is used to convert the voltage at a certain level when the day light is out. A diode is also connected in reverse biase so that the charging can be shut down by itself when the voltage level comes down under a certain level defined by the microcontrolle coding.

INTRODUCTION

Solar energy is the most viable renewable energy that we have. In our country we have limited resources to produce energy. Solar energy can play a vital role to mitigate this problem. Now a days daily need of electricity is about 5900MW, where we produce nearly 5200MW [1], so we have a shortage. So we need another source to get electricity (like solar energy and power system). In Bangladesh there are so many NGOs and also some government organizations that provide the solar energy and power system (with the set of solar panel, battery, and inverter) to the rural areas where till no electricity connection has been established yet and in many areas where the problem of electricity is more severe than in other areas. But they don’t provide the solar charge controller (SCC) with their solar panel set because of its high cost and difficulty in operating (exception in the city). The consequences of this lacking are faced by the poor people of rural areas who have taken the solar system. They get the battery problem after some days due to the charging and discharging problem. Due to this problem the battery lifespan gets reduced to a few days and the need arise to replace the old battery in short period of time. Thus the operating cost is increased for the poor people in the rural areas. This cost could have been reduced if a solar charge controller device was used, which we proposed here. So based on the low cost, better protection, availability and reliability this SCC model is designed and implemented for the betterment of our solar power and energy system to improve the present condition of electricity in Bangladesh.

The primary function of a charge controller is to protect the battery from overcharging and over discharging in a stand-alone PV system [2]. Lots of studies have been conducted about the charge

1 Graduate student, University of Information Technology and Sciences, Dhaka, Bangladesh Sabbir.jobs.eee@gmail.com2 Graduate student, University of Information Technology and Sciences, Dhaka, Bangladesh hemal.uits@yahoo.com3 Phd grade student at University of Ulongong,Australia,Ex assistant professor at University of Information Technology and Sciences, Dhaka, Bangladesh3smknazrulislam@facebook.com

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controller. These studies have been documented in the literature. Harrington and Dunlop (1992) analyzed the typical strategies for battery charge regulation in stand-alone PV systems and conclude that the battery information is very important in designing PV systems [2]. Ullah et al. (1996) focused on the design of a super-fast battery charger based on National’s proprietary neural network based neural fuzzy technology. They compared their method with conventional fast chargers and indicated that their method reduce the charging time [3]. Masheleni and Carelse (1997) designed an intelligent charge controller, incorporating an SGS–Thompson microcontroller, ST62E20 and discussed the advantages of such charge controllers [4]. Hsieh et al. (2001) proposed a fuzzy-controlled active state of- charge controller (FC-ASCC) for improving the charging behavior of a lithium–ion (Li–ion) battery. Tesfahunegn et al. (2011) proposed a new solar/battery charge controller that combines both MPPT and overvoltage controls as single control function. They conducted two case studies in Simulink/Simpower, first to evaluate the performance of the designed controller in terms of transient response and voltage overshoot. Secondly, realistic irradiance data is used to evaluate the performance of the developed charge controller in terms of parameters such as PV energy utilization factor and overvoltage compared to the conventional hysteretic on/off controller. They achieved good transient response with only small voltage overshoot, better in terms PV energy utilization and same level of overvoltage control [5]. There are some applications which are use MPPT controller [6-8]. Dakkak and Hasan (2012) analyzed a charge controller based on microcontroller in stand-alone PV systems and they conclude that such systems reduce the power consumption for charging battery and give flexibility to the designer [9]. Karami et al. (2012) focused on the load type and suggest new methods to reach the MPP depending on the load state and the development of the PV array mathematical model. They analyzed the effect of temperature and irradiance on the battery charger and showed the difference between the direct-coupled and the indirect-coupled applications of a PV panel [10].

This project implements this vision of implementing, designing and controlling of a digital solar battery charge controller which will be automatically ON/OFF on the pre preprogrammed voltage levels in the microcontroller based circuit, which will help getting rid of overcharging, which is set as upper cut of voltage 13.8V and lower cut off voltage at 9V. This is because the battery get hampered by overcharging and the load becomes unstable at low voltage. There will be two output as load which are +12V and +6V. So, any kind of these rated voltage device may be used as load. The circuit will also perform short circuit and overload protection.

1. FLOORPLAN & MATERIAL

Before proceeding to the technical work, it is mandatory to do some frame work that help to understand the research well. We first find out some objectives that will decide the future of the project. From this view, the ultimate objective of the project is determined to make such a system that will charge and discharge automatically. It was also a primary decision to make the system in such a way that it will be disconnected automatically as the voltage level will go beyond +13.8V and lower then +9V. As the system is an automatic system, then the components (Table-1) used in the making of the system are directly or indirectly connected with the microcontroller to retrieve input data and drive output according to the microcontroller program instruction assigned inside the program code of microcontroller PIC12F675.

Table 1: Components of the system

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Components Reference ValueResistor R1toR11, RV1 470Ω,1kΩ(4),

7kΩ,10kΩ(3),33Ω,3kΩ,5kΩ

Capacitor C1,C2,C3,C4 220µF(2),1nF,7pF

Integrated circuit U1,U2,U3 PIC12F675,GND72LDS,MIC34063

Diode D1,D4 D1(status), D4(charging)MOSFET Q1,Q2 IRF540(2)

Miscellaneous Voltage regulator, Transistor,Rectifier

L78L05, BC547,1N5817(3)

The logic diagram of the circuit operation is in figure 1 and the design algorithm of the system is shown in figure 2

Fig 2: The logic diagram of the controller

Here, in the system there is a solar panel which is connected to the main circuit which is originally designed on the basis of microcontroller PIC12F675. The previous design of the system was also included with conversion system with a DC-DC converter but the new technology is used here has made it far more innovative and flexible to use. For convenience the previous design of solar battery charging system has also included here in figure-3 [8].

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Figure 2: Modern Design algorithm of solar charging system.

Figure 3: Earlier Solar battery charging system block diagram.

In the earlier battery charging system no intelligent system was included. So, the system was almost manual where the modern design boasts an automatic system with the aid of a microcontroller. However, some problems occurred during the experiment, but they were not any deterring factors.

2. CIRCUIT DESIGN & CODING

A power supply with a solar panel or DC voltage source is constructed to establish a dc voltage of +12V (Figure-4) to provide necessary biasing of microcontroller and other circuitry. As the design was simulated through software and hardware included with a solar panel though in real project. Two mono colors Light Emitting Diode (LED) are used connected with the battery terminal. Here, one LED (red) which is showing the current status of the battery while the other (green) is showing the output to another end. Here, one sentence should mention that, the 2nd LED will blink only when the battery voltage will find itself under the minimum voltage and turn it on charging states automatically.

There are two output terminal in this device are applied. One for the +12V terminal and the other one is for the +6V terminal. This is because, sometimes it seems that it is necessary to have different voltage levels for home appliances. One LED (D1) will blink very fast when the charge is full and vice versa it blinks slowly when the battery voltage is under the minimum desired level. Another LED (D4) is connected as the output of +6V terminal. The output terminals are as follows: J2 is for +12V output terminal and J3 is for +6V output terminal.

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From the figure-3 a power supply section is used to a +12V battery for storing charge. A pin from microcontroller is connected with the voltage regulator (72LDS) through R5 and another line is connected through capacitor C1 from battery to solar panel. Another capacitor C2 is connected to the microcontroller and to regulator. Then, the diode D1 has made a connection between 72LDS and microcontroller pin 2. It will result in blinking when the battery will start supplying to the load. A resistor RV1 is connected along with capacitor to restrict extra charge storing into battery.

Figure 4: Schematic of microcontroller based solar battery charge controller.

The DC-DC converter consists of the power circuit and control circuit, for power conversion. Here, the transistor (mainly switch) switches the input DC voltage according the signal from the main controller and then supply it to AC voltage to the transformer. While the transformer changes the AC voltage and rectifies it through the diodes. In the main circuit schematics DC load side D2 and D3 are in same direction. This is the design which resists the voltage supply to the load when the voltage level goes down to the minimum level.

The design was fully microcontroller based and simulated by using Proteus as mentioned earlier. The program was written in CCS Professional edition. It was not too complicated to write the program. During the programming we experienced some interesting things like setting voltage level. Here the program has been summarized in Table-2 for the convenience of the reader. At last when we completed the circuitry then we moved forward to the next step to observe the implementation. Here, the implementation of the circuitry is first shown with the software to test the lower cut off voltage and upper cut off voltage.

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Table 2: Program code for the designed system

3. RESULTS & DISCUSSION

Figure 5 showed the lower cut off voltage when voltage across battery is less than or equal 9V. It secures the battery to be charged again. In the figure it has been shown with a bolded line.

Figure 5: simulation result of lower cut off voltage (discharging state ≤ 9V).

Figure 6: simulation result of upper cut off voltage (charging state ≥ 13.8V)

Figure 6 displays the upper cut off voltage which represents the voltage level of the battery does not exceed 13.8V. It secures the battery's safety and overload protection. The microcontroller pin no 6 senses this operation. The practical operation has been done using a DC fan (+12V) and a green LED (+6V) as a load. Figure 7 showed the practical circuit and the resultant output is shown in figure-8 by connecting a +12V load. Here, in this circuit we have used a green LED as +6V load. When voltage level decreased to below +9V across the battery then the +12V load (fan) will automatically be disconnected and red LED will start to blink as well as green LED will blink as a +6V load. Then the battery will again start taking charge from the solar panel and will be charged until the battery voltage reaches to +13.8V. This phenomenon is shown in figure-9.

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Figure 7: The circuit of charge controller for solar panel

Figure 8: A 12V load (fan) connection with the circuit and a DC voltage source as the supplier

(Solar panel).

Figure 9: +12V load (fan) is disconnected at the cut off voltage (≤ 9V) automatically and battery

starts charging representing green LED is blinking (+6V).

4. CONCLUSION

The achievements and new modifications of this project are:

[1] The total system is automated, intelligent and well controlled to its operation. [2] LED shows the battery state, overload or short circuit condition.[3] The circuit can handle maximum 22A of current for load using high efficient power

MOSFET (IRF540).[4] Silver coated heat sink is used in the circuit attached with the MOSFET ( IRF540) since

this kind of circuit runs all through the day outside with high humidity and little risk of burn.

[5] The circuit is very light and thin which assures its portability.[6] The total system is integrated compactly on a PCB board. A very cheap microcontroller is

used, which makes it more desired by customers than any other product of the market.

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Our future research direction is to determine the automatic recording and monitoring of the temperature and insolation level on the module to predict the maximum power of the module and converting the whole system into a single integrated circuit.

5. REFERENCES

1. http://www.bpdb.gov.bd/bpdb/index.php?option=com_content & view=article & id = 126 & Itemid = 17.

2. S. Harrington, J. Dunlop (1992), Battery charge controller characteristics in photovoltaic systems, Aerospace and Electronic Systems Magazine, IEEE, Volume: 7 , Issue: 8, p:15 – 21.

3. Z. Ullah, B. Burford, S. Rahman (1995), Fast intelligent battery charging: neural-fuzzy approach, WESCON/'95. Conference record. Microelectronics Communications Technology Producing Quality Products Mobile and Portable Power Emerging Technologies.

4. H. Masheleni and X. F. Carelse (1997), Microcontroller-Based Charge Controller For Stand-Alone Photovoltaic Systems, Solar Energy Vol. 61, No. 4, pp. 225–230.

5. S. G. Tesfahunegn, P.J.S. Vie, O. Ulleberg and T.M. Undeland (2011), A simplified battery charge controller for safety and increased utilization in standalone PV applications, International Conference on Clean Electrical Power (ICCEP).

6. C. Hua, J. Lin, C. Shen (1998), Implementation of a DSP-Controlled Photovoltaic System with Peak Power Tracking, IEEE Transactions On Industrial Electronics, V. 45, No. 1.

7. C. R. Sullivan, M. J. Powers, A (1993), High-Efficiency Maximum Power Point Tracker for Photovoltaic Arrays in a Solar-Powered Race Vehicle, Power Electronics Specialists Conference.

8. D. P. Hohm, M. E. Ropp (2000), Comparative Study of Maximum Power Point Tracking Algorithms Using an Experimental, Programmable, Maximum Power Point Tracking Test Bed, Photovoltaic Specialists Conference.

9. M. Dakkaka and A. Hasana (2012), A charge Controller Based on Microcontroller In Stand-alone Photovoltaic Systems, Energy Procedia V. 19, pp. 87 – 90.

10. N. Karami, N. Moubayed and R. Outbib (2011), Analysis and implementation of an adaptative PV based battery floating charger, Solar Energy, IEEE, V. 3, pp. 400-404.

Sabbir Ahmed(Author): Sabbir Ahmed was born in Dhaka,Bangladesh in 5th

November,1990.He completed his secondary school certificate(SSC) from Rampura Ekramunnessa High School,Dhaka,Bangladesh in 2005 and got golden GPA 5.0 from science.After completing SSC he just admitted into Notredame College,Dhaka,Bangladesh and got GPA 4.30 as well from science background.In that time of college he was a proud member of Notredame Science club,natur

study club,english club and debate club.After passing HSC he got admitted into Electronics and Electrical Engineering department at University of Information Technology and Sciences, Dhaka, Bangladesh.He was very keen to learn, well disciplined and regular to his classes.He was 99%

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present to his all 4 years bachelor degree course classes. At the end his hardwork was successful and he CGPA 3.94 on a scale of 4 which is very rare in his department.He got 9 departmental scholarship out of his 11 semesters which is usually rewarded as ‘Vice Chancellor award’.The major subject of his study was ‘power electronics’ and minor was ‘Communication engineering’He did an internship at Dhaka Electric suply company (DESCO) and now looking for a power electronics related job.Now Mr.Sabbir is heavily engaged with power and communication related research papers.His major filed of ineterests are photovoltaic cells, renewable energy,PLC,Radio frequency,3G network transmitting and Power factor correction in home and industry,Fire extinguishing and automated alarming system,MC based Water treatment plant and more.

Mr. Sabbir is now trying to get a membership from IEEE.He is already a member of IEB(engineers institute of Bangladesh).Right now he is involed in the campus club called E2C formed by the EEE department.This club usually organizes various Electrical workshop enhancing educational and practical knowledge among them.The club has produced more than 35 Electrical,Electronics microcontroller and robotics based successful projects.Every year the univisity’s main attractive shows are being done by this club. Mr.Sabbir is trying to acquire his Master’s degree from foreign country.If he gets proper funding he will have master degree Industrial Electronics .He also dreams to do a PHD and serves his country as well.

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present to his all 4 years bachelor degree course classes. At the end his hardwork was successful and he CGPA 3.94 on a scale of 4 which is very rare in his department.He got 9 departmental scholarship out of his 11 semesters which is usually rewarded as ‘Vice Chancellor award’.The major subject of his study was ‘power electronics’ and minor was ‘Communication engineering’He did an internship at Dhaka Electric suply company (DESCO) and now looking for a power electronics related job.Now Mr.Sabbir is heavily engaged with power and communication related research papers.His major filed of ineterests are photovoltaic cells, renewable energy,PLC,Radio frequency,3G network transmitting and Power factor correction in home and industry,Fire extinguishing and automated alarming system,MC based Water treatment plant and more.

Mr. Sabbir is now trying to get a membership from IEEE.He is already a member of IEB(engineers institute of Bangladesh).Right now he is involed in the campus club called E2C formed by the EEE department.This club usually organizes various Electrical workshop enhancing educational and practical knowledge among them.The club has produced more than 35 Electrical,Electronics microcontroller and robotics based successful projects.Every year the univisity’s main attractive shows are being done by this club. Mr.Sabbir is trying to acquire his Master’s degree from foreign country.If he gets proper funding he will have master degree Industrial Electronics .He also dreams to do a PHD and serves his country as well.

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