Charging control circuit made by solar energy

To generate electricity using solar energy, the following conditions must be met: 1. Photovoltaic panels that convert solar energy into electricity; 2. Batteries that store the electricity; 3. An optimal charge controller to maintain battery life; 4. An inverter that converts direct current into alternating current.

The configuration of a solar power supply device is as follows: 1. Photovoltaic panel GL136 (Japan), size 1291mmx3328mm, weight 5.6Kg; maximum output 53W, maximum output voltage Vpm=17.4V, maximum output current Ipm=3.05A. 2. The battery uses a 12V, 150Ah automotive maintenance-free battery. 3. Charging controller (self-made). 4. 300WDC-AC inverter (finished product).

The following introduces a homemade charge controller.

●The overcharge and overdischarge detection circuit
stops charging when the battery voltage reaches 14.5V, and disconnects the load when it is lower than 10.5V. The battery voltage detection uses four comparators NJM2901 (IC2), and the 5V reference voltage is provided by NJM431 (ICl). When the comparator IC2a ​​detects overvoltage, the photocoupler Phl turns off the light-emitting side to cut off the light-receiving side, and the two MOSFETs Tr2 and Tr3 are turned off, cutting off the charging current of the photovoltaic panel to avoid overcharging; at the same time, LED1 lights up. IC2b controls LED2 to display the voltage rise reminder. IC2e controls LED4 to display the voltage drop reminder. IC2d detects the low voltage of the battery due to overdischarge, and LED5 monitors the low voltage; at this time, the two MOSFETs Tr4 and Tr5 are turned off to cut off the load to avoid overdischarge. LED3 indicates that the voltage is within the normal range, and IC2b is turned on and IC2C is turned off.

Turn the potentiometer VRI, and LED1~LED5 will light up in sequence, indicating that this part of the circuit is working normally.

●Charging circuit
When the light receiving side of the photocoupler Phl is turned on, Tr2 and Tr3 are turned on to form a charging circuit. Two MOSFETs are used to shunt the charging current to reduce the influence of the on-resistance of the field effect tube.

●Charging circuit diagnostic device
Since photovoltaic cells are connected in parallel, when one of the cells is damaged or has poor contact, insufficient charging will occur. Here, the four photovoltaic cells are divided into two groups, and the charging currents of the two groups are basically the same, which is used as the basis for detecting abnormalities in the charging circuit. When the charging circuit is abnormal, the voltage drops on the sampling resistors R32 and R33 are not equal. This difference is amplified by the differential amplifier IC3h, and IC3e and IC3d are connected to form a window comparator. As long as LED6 is lit, it means that the photovoltaic cell is abnormal.

●Charge and discharge indication
The charging current generates a voltage drop through the sampling resistor R31, which is amplified by IC3a and lights up LED7 to indicate the charging status.

LED8 is used as output indicator light (discharge).