Solar Voltage Regulator Functions
A solar cell voltage regulator serves as a crucial component in off-grid solar systems, primarily preventing battery overcharging while regulating and controlling the voltage supplied from the solar panel to the batteries and connected electronic devices.
Simple and Economical Comparator for Solar Cells
This device is intentionally designed as a straightforward and cost-effective “comparator,” specifically for use in solar cell power supply setups requiring a rapid indication of either “too low” or “just right” voltage levels. The circuit comprises minimal components: a 5-V regulator, two transistors, two LEDs, five resistors, two capacitors, and a small battery. While the schematic mentions a 4-V battery, 4.5 V (three alkaline cells in series) or 3.6 V (three NiCd cells in series) are also suitable. The choice of voltage regulator IC1 primarily depends on factors like the solar cell size, their quantity, and the connected equipment’s current draw. While the low-dropout 4805 is recommended here, alternative regulators may also function effectively as long as they align with the solar cells’ output voltage.
Complementary Transistor Selection
Transistors T1 and T2 in this circuit are complementary, meaning there’s one PNP (BC557B) and one NPN (BC547B) type. However, any equivalent small signal transistors found in a collection of spare parts would likely suffice, offering flexibility in component selection.
Adjustable Voltage Dividers for Thresholds
To accommodate different transistor types, their gains, or to match specific voltage thresholds, adjustments might be necessary for the voltage dividers R1/R6 and R3/R4. In the provided schematic, LED D2 illuminates fully when the voltage surpasses 5 volts. On the other hand, LED D1 lights up when the voltage falls below approximately 4.2 volts. In the intermediate voltage range, both LEDs shine dimly, creating a transitional zone. To enhance the warning system, a buzzer or another alerting device could be connected across the terminals of LED D1. Offering a more noticeable warning if the voltage drops below the operational limits. The circuit’s current consumption is around 20 mA at 5 V and decreases as the voltage supplied by the solar cells decreases.