SIMPLE SOLAR LAMP

Here is the simple solution to make an automatic Solar powered lamp. It automatically switches on two high power White LEDs in the evening and stays on for 6 hours using a 6 volt 4.5 Ah rechargeable battery.A 12 volt solar panel is used to charge the battery during day time. The battery is connected to the input line through the NO and Common contacts of the relay. Diodes D1 and D2 drops 1.4 volts and charge indicator LED uses 1.8 volts. Relay also drops some voltage so that around 8 volts will be available for charging the battery. The high value (4700uF) Capacitor C1 act as a “buffer” for the clean switching of the relay and also prevents “relay clicking” when the input voltage reduces momentarily.

Simple Solar Lamp Circuit diagram

During day time, the solar panel generates 12 volt DC which makes the relay active and the NO (Normally Open) contact makes connection with the common contact. This completes the current path to the battery. Two 1 Watt power LEDs are connected to the NC (Normally Connected) contacts of the relay. When the relay energize, the NC contact breaks and LEDs do not get power. Resistor R2 ( 18 Ohms 1 Watt) drops the LED current to 330 mA. The LEDs are rated 350 mA at 3.6 volts. With 3 volts and 250 mA current, these LEDs can give adequate brightness.