Low-cost Solar Cell Boost Converter

 

Here are very simple build electronic circuit project of Low-cost Solar Cell Boost Converter circuit. The boost converter is used to charge batteries from low voltage solar   arrays. Results were obtained using 3X3 cells that deliver about 400   millivolts at 1 amp. The pictured panel array contains 20 cells in series   and generates about 8 watts at 8 volts in bright sunlight and was assembled   on a 12 X 16 picture frame. Efficiency of the converter measured 87% and   delivers almost 600 milliamps into a 12 volt SLA battery. Efficiency drops   to about 72% using 4 single cells in series (pictured above) charging the   same 12 volt battery at around 70mA. The current was a little low due   to a couple broken corners. A third test was made using a single cell at   0.4 volt charging a 6 volt battery, but efficiency was only about 55%.   The cells were purchased from solarcells101.com in slightly damaged   condition with chipped edges and a few tiny cracks, but still perform well   and sell at discount. There are also many good deals on ebay.

The 10Khz oscillator and drive circuit obtain power from the battery under   charge which should be grater than 4 volts. The output stage (mosfet and   inductor) obtain power from the solar array and produce a charging current   through the schotty diode (VSK 330). Efficiency is improved with 220uF   capacitors added across the input and output. A 12 volt zener diode and   120 ohm resistor were added to protect the circuit from excessive voltage   in the event the battery is disconnected during operation. Additional   protection is obtained with the TL431 voltage reference diode which limits   the output voltage to 18 volts. If the output exceeds 18 volts, the cathode   of the TL431 falls, stopping the oscillator until the output falls below   16 volts.

Low-cost Solar Cell Boost Converter Circuit Diagram:

In operation, the duty cycle of the switching waveform is adjusted with   the 100K pot for maximum current into the battery. This adjustment can be   made by monitoring the voltage across the 1.5 ohm resistor and adjusting   for maximum voltage. This should be the optium setting where efficiency   is highest and maximum power is extracted from the solar array. Regulation   is not used so the optimum setting may need adjustment as conditions change,   lighting conditions, temperature, battery voltage, etc. Some loss occurs in   the 1.5 ohm resistor, maybe 5% which could be reduced with a smaller value   resistor, or a milliamp meter with low resistance.

Most parts are fairly common except maybe the 5mH inductor. I used a ferrite   torroid core from a scrap PC switching PS. The core measures 1.5 inch   outside diameter by 5/8 thick. The windings were removed and replaced with   25 turns of the same 18 gauge wire. The resistance measures 25 milliohms.   The inductor value is fairly tolerant and can be most anything from 1mH   or greater if the resistance is low and the core doesn't saturate with the   peak current. Larger inductors will have lower peak currents but higher   resistance for the same size.