Solar Charge Controller Circuit Diagram
Here is the schematic diagram of Solar Charge Controller (Solar Regulator). You may want to print it out, and then go on reading. Solar Charge Controller (Solar Regulator) is designed for 12V systems employing panels of up to 7A total current, and loads of not over 20A. It can be easily modified for greater currents.
U1A compares an adjustable sample of the present battery voltage to a 5V reference from a highly stable source. According to the result, it controls the power transistors Q1 and Q2, which shunt off the excess power generation from the panel. A diode (D1) avoids battery voltage to go back to the panel under no-light condition. To avoid imprecise voltage control due to varying diode drop, the sample is taken from the battery side, even if this means a very small power waste.
The power resistors R1 and R2 are dimensioned in such a way that under maximum shunting, these resistors will dissipate almost all power (about 100W total), leaving the transistors running cool. The highest dissipation in the transistors happens when the regulator is dissipating half of the panel output; in this case, each transistor will dissipate about 12W.