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Simple Solar Lamp circuit

2015-01-08 00:13  
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Here is the simple solution to make an automaticSolar powered lamp. It automatically switches on two high power White LEDs in the evening and stays on for 6 hours using a6 volt 4.5 Ahrechargeable battery.

A12 volt solar panelis used to charge the battery during day time. The battery is connected to the input line through theNOandCommoncontacts 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

Simple Solar Lamp Circuit diagram

During day time, the solar panel generates12 volt DCwhich makes therelay activeand the NO (Normally Open) contact makes connection with the common contact. This completes the current path to the battery. Two1 Watt power LEDsare 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 to330 mA. The LEDs are rated 350 mA at 3.6 volts. With 3 volts and 250 mA current, these LEDs can give adequate brightness.

1 Watt Power LED

In the evening, current from the solar panel stops andrelay de – energize. At the same time, the NC contact of the relay gets power from the battery through the common contact and LEDs turn on. Theoretically, the battery can power 12 hours with 350 mA current, but the battery voltage and current reduces drastically. So it is better to turn off the lamp after 5 or 6 hours using the switch S1.
Use a small 6 volt 100 Ohms PCB relay to make the lamp unit compact. The Solar Lamp circuit including the relay can be enclosed in a small box. If a reflector is fixed behind the White LEDs, intensity of light can be increased. Use jack and socket to connect the solar panel with the circuit.

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