PWM SOLAR CHARGE CONTROLLER CIRCUIT AND TECHNOLOGY TRANSFER

PWM SOLAR CHARGE CONTROLLER CIRCUIT DIAGRAM

This post explain about the working of pulse width modulation  solar charge controller along with inverter control.

INPUT PROTECTION  :     Built in Blocking Diode to prevent SPV array from reverse polarity and

                               to prevent reverse flow of current from Battery

       (SPV SIDE)  - Built-in MOV protection against HIGH                                    VOLTAGE    LIGHTNING during rainy season

CHARGING                 :        MOSFET Based PWM Charging (microcontroller controlled)

         - BOOST CHARGING till the battery voltage reached 14.5V

          - ABSORPTION MODE to charge the battery for 100% energy storage

           - CHG. ON when PV Volt goes up 10V-11V

CHARGING LED          :        - LED Flash during boost nad LED constant during absorption

            - LED OFF when charging is OFF or PV Volt below 10V

LOAD CONTROL         :    - LOAD connector continous active in NORMAL during Day or Night

       - LOAD OFF during lo-batt cut-off at 9.5V or 10V

        - LOAD reconnect when battery voltage goes up 12.5V or                                           above

CIRCUITRY                :      - Microcontroller based electronics

      - MOSFET based load control switch and charging switch

      - PWM charging for 100% energy storage compare to ON / OFF type                charge controller

working of Pwm solar charge controller :

This is a PIC16f72 microcontroller based Solar Charge Controller with two steps charging algorithm. 

a) When the battery is < 14.2V, the circuit start charging the battery in Boost Mode with full current from the Solar Panel.

 b) When the battery voltage Reached to 14.5V the circuit charge the battery Trickle mode, in this mode the circuit maintaintain the Battery voltage @14.5V untill the panel provide the enough voltage from Sun.

 Now let us discuss about the circuit operation. The whole control circuit is powered from battery bank (12V to 48V). Battery is connected through a Fuse of rated capacity for protecting the circuit from reverse polarity, a diode D4 is used for that whenthe battery is reverse connected the diode D4 conduct and Fuse blown. 

A series pass regulator is comprising Q3, R3 and D2 used to get 12V DC from Battery (when battery bank is 24V or 48V), 12V is used to power the Inverter control Relay and PWM Switch (Q6 and Q8). A 5V regulator comprising RG1 is used to power the microcontroller. 

Here the heart of the circuit is U1 PIC16f72 8-bit microcontroller. As about its architecture and pin detais refer to its Data sheet .

 U1 is clocked with an external crystal oscillator X1 (4Mhz), C11 and C12. Pin1 of U1 is for power on reset, pin 25 to pin 28 (Port RB4 - RB7) are for LEDs (Relay on, Lo-Batt, Chg. status, PV ON). 

Pin 12 (Portc1) is used to power On / Off the inverter control Relay. Pin 20 of U1 is VDD pin and 5V is fed to this pin from RG1 (7805), Pin 19 is ground. 

Now let us discuss about the charging algorithm and working of it. 

Q1 and Q2 a n-channel MOSFET is used as a charging switch, DC voltage from panel is fed to this MOSFET switch through a Schottky doide D1, this diode is used so that the battery voltage should not pass to panel in night time.

 When the battery voltage is less than 14.2 V, the Mosfet Q1 and Q2 is fully ON, and Full current from panel is fed to battery through D1 and Q1, this is called BOOST mode, and in this mode Chg Led is flashing. 

Q1 and Q2 are connected in the high side of the supply line and its source pi is floating, so to switch ON the Mosfet Q1/Q2 its gate pin require the double voltage of Vcc so that the voltage across its gate and source pin should be equal to Vdd. 

Here a voltage doubler circuit is incorporated using D5, D8, Q4, Q5 and Q7. a 1kHz squarewave pulse is generated from pin 14 of U1 and is further fed to Q7 and Coplimentary totem pole pair (Q4 / Q5). These Q4 / Q5 are used to charge and discharge C9 through D5 and D6, hence the voltage across the capacitor C20 is almost double of Vdd. This voltage is used to switch ON the MOSFET Q1.

 Now let us discuss about the PWM control of the circuit. the microcontroller intially switch ON the MOSFET Q1 fully to pass the full current on to the battery, and simutaneously sense the battery voltage at its pin 3, as soon as the battery voltage reaches to 14.2V absortion mode starts working. 

Pin 13 of Microcontroller is proving the PWM pulse and controlling the duty cycle of ON and OFF time of Q1 so that the controller maintain the battery voltage @14.2V and to keep the charging in Absorption mode.

Intially when the charger is ON the pin13 of controller increases its duty cycle with a small time delay from 0% to 100% duty cycle, which in result a delay charging current increase. When the output from pin13 of U1 is 100% dutycycle, then transistor Q8 is On and which in turn makes OFF Q8, and hence the MOSFET Q1 is fully ON. 

Simultaneously the microcontroller senses the battery voltage at its pin3, when the battery voltage is >14.2V the the PWM starts decreasing its output untill the battery voltage is equal to 14.2V. 

Relay: Here a relay is provided for user if they want to switch OFF the mains and run the inverter through battery, which in turn to save the electricity. the relay becomes ON when the battery voltage goes above 14.5V and becomes OFF when battery voltage goes below 11V.

BOM :

PCB & Wiring :

INDUUCTOR DATA:

20AMP :

15-TURN (17SWG)

T-27 TOROIDAL

10AMP :

20-TURN (18SWG)

T-22 TOROIDAL

30AMP :

10-TURN (16SWG)

T-30 TOROIDAL

Testing:

 1) Do not connect solar panel initially, microcontroller (U1), connect DC power supply with current set at max 1-amp, coonect it to the battery terminal, and switch ON the supply,

2) measure voltage at emitter of Q3 it is 11.6V, pin3 og RG1 it is 5v DC, pin1 of U1 it is 5V, pin20 of U1 it is 5V, pin 19 of U1 it is 0V.

3)switch OFF the supply connect U1 on its base, switch ON the supply check squarewave at pin14 of U1,if its coming check voltage atacross C10, it is almost double the battery voltage. If the squarewave is not coming from Pin14 of U1 the replace the U1, if the squarewave is there but the voltage across C10 is equal to battery voltage then check Q7, Q5, Q4, D5 and D6.

4) Now remove DC power supply from battery connector and connect it to PV connector and connect battery to battery terminal, switch ON the power supply and increase the power supply voltage from to 10V, At 10V or above the charging LED starts blinking and PWM pulse from pin13 of U1 start increasing.

You can purchase  hex code and pcb layout for 25 usd , for source code contact sandysplash230@gmail.com