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Mini Solar Garden/Street Light

Here’s another do it yourself project of an automatic mini solar garden/street light. This design belongs to the ‘renewable energy’ category, and is wired around a handful of inexpensive electronic parts. This nifty light circuit has two key components: a solar panel with a peak output voltage of about 6 V, and a Li-Ion battery with a voltage between 3.7 V and 4.2 V.

Circuit Diagram

Circuit

At daytime the voltage supplied by the solar cell reaches the peak value typically around 6 volts, so the Li-ion battery gets charged through diode D1 and resistor R1 connected in series. At the same time transistor T1 is closed too causing transistor T2 to be open and white LEDs to remain dark. If the voltage supplied by the solar cell drops T1 opens and T2 closes, connecting the ‘white LEDs to the battery through resistor R5.

Feel free to select the white LEDs—the prototype had a bunch of 4mm White LEDs (a total of 15 in parallel). The battery charging rate as well as the intensity of the white LEDs may be adjusted by adapting R1 and R5. Zener diode ZD1 prevents excessive battery charge voltage levels. Switch S1 when opened guards the battery from being discharged when the light is in storage, or not in service for a long time.

Parts List

  • SP1: 6V (>100mA) Solar Panel
  • BAT: 3.7V/700mAh Li-Ion
  • T1,T2: S8050
  • D1: 1N5007
  • ZD1: 1N4731A (4.3V)
  • R1: 10R/1w
  • R2: 10K
  • R3: 100K
  • R4: 3.6K
  • R5: 2.2R /1w
  • C1: 4.7uF/16v
  • S1: SPDT Slide Switch
  • LED: 4mm Oval White (x15)

Key Components

Construction Hints

A small prototyping circuit board is enough for the construction of the whole electronics, while the white LEDs can be mounted on another piece of rectangular strip board. However, here’s the proposed pcb artwork (not to scale) by the author, good for those want to build and sell the light as a commercial product. In the given pcb, all resistors should be mounted in vertical direction.

PCB artwork

Finally, try to find out a cute and water-proof enclosure for your own mini solar garden/street light!

Note: You need to credit the author/circuit designer and the website when using this circuitry as the core element of an end-user product. If you prefer not to include the attribution, you must submit a request through proper channel!

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2 Comments

  • Great project I will try it. but I wish to find out if the battery and 15 led specification can go though the night. that is 12 hours?

    • NGANG: See, this one is primarily designed as a mini solar garden light/street light with limited runtime. That’s why backup time is not indicated in the article. However, it’s easy to modify the circuit with a higher-capacity Li-Ion battery (2700mAH @ 3.7V, just as an example), naturally only after replacing the solar panel with another appropriate one (also keep an eye on D1 and R1). Thanks for your keen interest in my article, and the valuable feedback.