Simple Automatic Solar light

Solar powered devices are getting more and more popular these days. It is renewable and Eco-friendly kind of energy. One on the most popular application of solar power is the solar powered street lights. I made a very simple schematic of a solar powered light that can charge and turn on the light automatically.

About the Circuit

The circuit is very simple and easy to build. It only consist of 2 blocks. The first block is the simple charger circuit that charges the lead-acid battery to around 14.4V. For other battery voltages you can adjust the R2 value to match your battery voltage. You might wonder why there is no current limit on the charger circuit? Because the solar panel has maximum output current, unless that maximum output current is larger than the battery can take, you wont need an output current limiter.

The second block is the light switch circuit. It only works by detecting the solar panel output voltage and turn on the light when the solar panel output voltage drops to some level setting. That turn on level is set by R1 and R4 values. Take note that the values of these resistors are not yet optimized. R6 is optional and you can remove it if Q2 has a Vgs rating of 20V or higher. You can change Q2 for a smaller MOSFET if desired, just make sure that the Id and Vds is higher than your actual levels. For example if your light bulb is rated 1A and your battery is a lead acid 12V then a MOSFET with 2.5A Id and 25V Vgs rating should be your minimum requirements for selection of MOSFET.