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

A.S.M. Jiaul Hoque1*, Sheik Md. Kazi Nazrul Islam1,2, Md. Abubakar Siddik1, Sabbir Ahamed1

1University of Information Technology and Sciences (UITS), Dhaka-1212, Bangladesh 2University of Wollongong, Australia

*venus4erros@gmail.com

Abstract— In this study, a microcontroller based solar powered lead battery charge controller with efficient so-lar panel and some physical LED’s which can significantly states the condition of the battery and the whole cir-cuit is developed. It comprise of using microcontroller based charging algorithms. This project can be divided into two main parts: hardware and software development. The hardware development includes, solar panel con-nection, charging and control circuit. The software development include, microcontroller programming tech-nique, controller algorithms, Proteus analysis etc. A 12V-7A/10A DC battery charges frequently by the sun in the day and discharges in the night. The whole charging and discharging process automatically controlled by the preprogrammed microcontroller 12F675.The higher cut off voltage of the battery is set as 13.8V and the lower cut off voltage is set as 9V by the microcontroller coding for the battery and load safety. There are 2 output load connector of +6V and +12V connectivity. Using a 5W solar panel it took 6 hours to complete charging of a 12V generic lead acid battery. A simple 12V LED light is used as load output and the circuit gave 1.2A rated current and last longer than 4 hours. The blinking of LED indicates the battery states and even the short circuit condi-tion or overload condition of the circuit. The circuit can operate at a maximum current of 22A at the room tem-perature with power MOSFET IRF540. Proteus ISIS 7.7 is used for system design and simulation, and CCS professional Edition (software) is used to write the program code and burning the microcontroller 12F675. Fi-nally, Proteus ARES 7.7 is used to design the printed circuit board (PCB), for practical implementation. Keywords— Microcontroller, Charge Controller, Solar Energy, Proteus, Code Controller Studio (CCS)

I. INTRODUCTION

Photovoltaic power systems, a promising source of energy for the future, are actually solar panels referred by the industry as solar electric modules or PV modules. The modules can be wired as series or parallel arrays to produce higher voltages and cur-rents. In general, standalone PV system also known as off grid system consists of a PV array which converts sunlight to direct-current electricity, a control system which regulates battery charging, discharging and operation of the load, energy sto-rage in the form of secondary batteries and loads or appliances. A charge controller is one of functional major components in PV systems which is used to maintain the proper charging voltage on the batte-ries. The charge controller regulates the charge to the batteries preventing any overcharging. So a good, solid and reliable PV charge controller is a key component of any PV battery charging system to achieve systems maximum efficiency. Currently there are some analogue solar battery charge controller in the industry which has no overcharging protector feature and thus the bat-tery damages quickly. There is no voltage level or charging LED indicator and no short cir-cuit/overload protector is present. People want smarter artificial intelligence which will work au-

tomatically. This is possible through the technology called microprocessor or microcontroller based system. The application of microcontroller based devices are continuing to rise with its greater processing speed and flexible control; and the elec-trical appliances are getting more miniaturized, less costly and low power consuming. Microcontrollers reduces the number of chips and the amount of wiring and circuit board space, which is useful to produce equivalent systems using separate chips. Furthermore, each pin of a microcontroller inter-faces several internal peripherals, with the pin function selected by software. This allows a wider variety of applications than single specific func-tions. This project implements, designing and controlling of a digital solar battery charge control-ler which will automatically ON/OFF on the pre-programmed voltage levels in the microcontroller which will be helpful to get rid of overcharging, set as upper cut off voltage at 13.8V and lower cut off voltage at 9V. The battery becomes damaged by over charging and the load becomes unstable at low voltages. There will be two output as load which are +12V and +6V. Any rated voltage device with-in this range may be used as load. The circuit will also perform short circuit and overload protection.

II. CIRCUIT COMPONENTS & DIAGRAM

A microcontroller PIC12F675 is used as the central unit of the system. Two LED (Light Emitting Di-ode) is used to sense the status of two different voltage levels.

Table 1 Components of the system

A power supply with solar panel or DC voltage source is constructed to establish a dc voltage of +12V to provide necessary biasing of microcontrol-ler and other circuitry. Two LED (red) are con-nected with the +12V terminal. Here, one red LED (D1) is showing the status of the battery and the other (D4) showing the charging or discharging state of the battery. Two output voltage of +12V & +6V are exist as it is sometimes necessary to have different voltage levels for our home appliances. The LED (D1) blinks fast when the charge is full and vice versa it blinks slowly when the battery voltage is low. It gives a clear view of the charging state of the battery. Another LED (green) is con-nected as the output of +6V. When the +12V out-put is available then the +6V LED will automati-cally blink as load. The two red LED are directly connected with the microcontroller. The output terminals are shown as J2 for +12V and J3 for +6V. J1 is defined as the input from solar panel or DC voltage source. The whole circuit diagram and schematic diagram are shown in the Figure1&2.

Figure 1: Circuit diagram of the System

Figure 2: Schematic diagram of the system

III. CIRCUIT DESIGN & CODING

3.1. DC input and Battery charging section

A solar panel or a DC voltage Source can be used as +12V dc power supply. A pin from microcon-troller is connected to L7805 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 L7805. A diode D1 is connected with L7805 and to pin2 of microcontroller. The capacitor C1 and C2 both are connected to the solar panel for storing charge to the battery. A resistor RV1 is connected to capaci-tor to restrict extra flow of charge to from solar panel battery. Another pin of microcontroller is connected to MOSFET (Q1).

3.2. DC-DC converter and the load side

The DC-DC converter consists of the power circuit and the control circuit, for the power conversion. In the power circuit, the switching transistor (MOS-FET is mainly used due to the high speed switching requirement) switches the input DC voltage accord-ing to the drive signal from the control circuit, and then supplies the AC voltage to the transformer. The transformer changes the AC voltage, and recti-fies it through the diodes. In the smoothing circuit, the on-off DC voltage after the rectification is smoothed, and it is then changed in the auxiliary battery. The control circuit controls the output vol-tage to output the specified voltage even in case there is a disturbed change in the main battery vol-tage. However, the auxiliary battery requires a pre-cise voltage charge to it. Since the voltage drop not negligible, the terminal voltage of the auxiliary battery is detected directly, and then the output voltage is controlled so that the voltage at the aux-iliary battery terminal reaches the specified value. This is known as "battery sensing control". In this case, the sensing point is switched from the aux-iliary battery terminal to the output terminal of the DC/DC converter. This is known as "converter

sensing control" or "local control”. In figure 3 the main portion of the circuit is shown. Here the +12V output terminal is referred as J2. Another output terminal of +6V is referred as J3. A DC-DC con-verter named MC34063A is referred as U3. From the figure, a connection is made from the pin6 of MC34063A to the microcontroller PIC12F675 through L7805. A diode D5 is connected to induc-tor L1 from the DC-DC converter. The DC-DC converter switches the MOSFET (Q1) to the DC voltage supply according to the signal of microcon-troller. A MOSFET (Q2) is connected to the output terminal. It is because, when the MOSFET get pulse from the converter it acts as switching device and then drive the DC voltage to the load.

Figure 3: DC-DC converter with load side

3.3. Input side and Output load side

When the solar panel or DC voltage source will plug in with the battery, it will charge the battery and D4 will show the charging status. When the battery will be fully charged D1 will show the sta-tus and the microcontroller (PIC12F675) will send the logic to the MOSFET to get switched on. Then the charge will start to flow to the output terminal (+12V, J2) through the MOSFET. Then the con-nected load will be in “on” state. The load will work until the battery discharges. When the battery voltage continues to discharge, the connected load will gradually come to the “off” state. When the battery voltage will decrease under +9V, the con-nected load will be completely disconnected, then the MOSFET will also be switched off. Similar case continued when the load will be connected to +6V, J3 terminal.

Figure 4: Input and output section

3.4. Programming the Microcontroller 12F675 (using CCS)

The 12F675 uses the built in feature EEPROM which erases the written program inside of micro-controller, without ultraviolet light. The software “CCS professional edition” is used to write the program for 12F675 and the following steps are followed.

Step 1: Using the software ‘“CCS professional edi-tion”, the program is typed; then it is compiled and after being successful, a HEX file is generated. The HEX file is generation is shown in Figure 5.

Step 2: Using the software the chip signature is checked which ensures the chip and using the EE-PROM (electrically erasable programmable read-only memory) feature of 12F675 the microcontrol-ler is erased.

Figure 5: writing microcontroller coding in CCS

Figure 6: Burning the Microcontroller by entering the program code

IV. RESULT & DISCUSSION

The objective of the project was to make a device that will control the voltage automatically without changing current. That means the device will keep the current at a constant value. When the voltage will be charged over +13.8V then the battery will be automatically disconnected from the microcon-troller through MOSFET (Q2). That means the MOSFET will be switched off. When the battery voltage will be less than +9V then the battery will reconnect to the solar panel through switching MOSFET (Q2). Two LEDs shows the charging status. It should be mentioned that when the vol-tage level is less than +9V then the load will be

automatically disconnected from the battery and if panel voltage is present there, it will start charging again.

4.1. Proteus ISIS 7.7 Simulation result

The output simulation result using Proteus ISIS 7.7 for Lower and Upper cut off voltage are shown in figure 7 & 8.

Figure 7: Lower cutoff voltage (discharging state) <9V

Figure 8: Upper cutoff voltage (charging state) >13.8V

4.2 Design of Printed Circuit Board (PCB)

To precede the design of PCB, the ARES tab of the Proteus ISSI toolbar is pressed and the total circuit components, their values and their information of interconnection are transferred to the Proteus ARES. The component tab is pressed to move in component mode and PCB designing is used from the list of components at left column. Design rules of the Proteus ARES for PCB design are shown in Figure 9, 10 & 11.

Figure 9: Pressing the ‘ARES’ tab of ISIS toolbar for PCB design

Figure 10: Proteus ARES ISIS 7.7 for PCB design layout

Figure 11: Proteus ARES ISIS 7.7 (upper view)

4.3 View of Practically Implemented System

The completed printed circuit board (PCB) design is printed on a tracing paper and fabricated on an insulating material for integrating the system com-ponents. The view of practically implemented sys-tem is shown in Figure 12 & 13.

Figure 12: +12V DC fan operating as load connected with DC power supply

Figure 13: Load is disconnected at lower cut off voltage and battery starts charging

A general comparison between the previous tech-nology and the implemented project is shown in Table 2.

Table 2: Comparison with previous work

V. CONCLUSION

An automated (artificially intelligent) microcon-troller based solar battery 12V-7A/10A charge con-

troller has been made successfully. The total sys-tem is automated, intelligent and controlled to its operation. Three LED's shows the battery state, overload or short circuit condition. The circuit can handle maximum 22A of current for load using high efficient power MOSFET (IRF540). Silver coated heat sink is used attached with the MOSFET (IRF540) as these kind of circuit runs all through the day in outside with heavy humidity and little risk of burn protection. The circuit is very light and thin which assures it as a portable device. The total system is integrated compactly in a PCB board and very chip microcontroller is used which makes it customer demanding rather than any other product of the market.

Further works may be focused on controlling and monitoring the voltage levels by using a LCD dis-play and a buzzer may add for low voltage, higher voltage, and short circuit or over load detection.

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