PAGE 131 OF 150 · POWER SUPPLIES & BATTERIES
Solar-Powered LED Lights
A panel charges a battery for night-time use.
LED SYMBOLTriangle points from anode to cathode; the arrows show light leaving the part.
How it works
A solar light has a small panel, a rechargeable cell, an LED and a control circuit. The panel charges the cell by day, and the same panel voltage acts as a sensor that switches the LED on when it becomes dark.
Sizing
A 1 W LED for 8 hours needs 8 Wh. A 3 W panel giving 4 peak sun hours at 70 percent efficiency produces about 8.4 Wh per day.
- Use a blocking diode so the cell does not discharge through the panel at night.
- A single NiMH cell is often boosted to run a white LED.
- Allow spare capacity for cloudy days.
Keep the panel clean and aimed at the sun.
REMEMBER
Size the panel for the energy used each night.Try it yourself
Sketch the circuit on paper first, calculate the values, then build it on a solderless breadboard using a low-voltage supply. Measure with a multimeter before you make anything permanent.
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