Solar Powered LED

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.

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.

In the evening, current from the solar panel stops and relay 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.

1 Watt High power LED

Use a small 6 volt 100 Ohms PCB relay to make the lamp unit compact. The 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.


About D.Mohankumar

D. Mohan Kumar M.Sc., M.Phil, is an Associate Professor from Trivandrum, Kerala, India. He has been guiding Post Graduate students in Animal Science research for the last 25 years in several premier institutions in Kerala, India. He is an avid electronics enthusiast and has been designing circuits for the past 20 years. In this period he has supported many electronics/electrical engineering students in their final year projects. He is a regular contributor to Electronics For You magazine which is South Asia’s largest circulating electronics magazine published from New Delhi. He is also contributing articles in and
This entry was posted in Chargers, Higher level Projects, Hobby Circuits, Home projects, LED, Light, Power supply and tagged , , . Bookmark the permalink.

9 Responses to Solar Powered LED

  1. Thank you for the circuits

  2. Ali Asghar says:

    nice 1

  3. Thomas PD says:

    Sir, I WOULD LIKE TO MAKE A SIMILAR CIRCUIT TO BURN SIX HIGH POWERED LEDs which will act as an inverter when power goes of. Could you help me with circuit and values of components. eiither solar powered or from electricity

    • D.Mohankumar says:

      Hello Thomas
      The High power LED requirs 3 volts and 100 mA current to give full brightness. You can connect the 6 LEDs in parallel each with a separate 10 Ohms resistor.Since the LEDs use large power, battery capacity is a factor. It is better to use 12 volt car battery or UPS battery for long time working.You can connect around 10 One watt LEDs like this

  4. Thomas PD says:

    there is still a problem. My aim is to power my home with same LEDs which must automatically turn on when power goes out. (Lights alone is sufficient). Is it possible to make the charging of the car batteries with solar panel? If so the rating of components will be different I suppose. coul you help me with the circuit and component values?

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