Are you a gardening enthusiast who loves admiring their plants at night? If so, a garden light is a perfect solution to illuminate your garden and appreciate its beauty even after sunset. However, running electrical wires through wet garden soil can be hazardous. That’s where solar-powered garden lights come in. These lights have a battery that charges through a solar panel during the day and powers the lights at night, providing a continuous cycle of energy.
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In this guide, we will show you how to build a simple and affordable DIY solar garden light. Unlike other circuits, we will keep the component count low to reduce costs and complexity. Let’s get started with creating our very own solar-powered garden light!
Solar Garden Light Design
Before we dive into the circuit diagram and component values, let’s first choose the type of garden light for our project. The voltage and current rating of the light will determine how our circuit can be designed.
We will be using normal Chinese LEDs with an operating voltage of 3.2V and a maximum forward voltage of 4.5V. By connecting two LEDs in series, the forward voltage will be 6.4V. Hence, we will use a 7.4V lithium battery as the power source for this project.
Solar Garden Light Circuit Diagram
The solar garden light circuit consists of two parts: charging and LED control. The complete circuit diagram is explained below.
For charging control, we use an N-Channel MOSFET (IRF540N) and a potentiometer (R1) to set the desired battery voltage level. A Schottky rectifier diode (SR160) is used to protect the battery from reverse polarity and block reverse flow during discharging.
To control the LEDs during dark conditions, we use a P-Channel MOSFET (IRF9540) whose gate is controlled by the solar voltage. When the solar cells produce voltage, the MOSFET remains off. But in darkness or at night, when the cells no longer produce voltage, the MOSFET turns on. This design eliminates the need for an LDR and comparator circuit.
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The LEDs are connected in a series-parallel configuration. Two LEDs connected in series double the forward voltage, while the current flowing through them is divided. We recommend using four parallel connections with two LEDs in series. Keep in mind that increasing the number of LED strings will affect battery backup.
Solar Garden Light Construction
To construct the circuit, you will need the following components:
- Lithium battery 7.4V (mAh depends on backup time) with built-in protection circuit
- LEDs with 3.5V forward voltage
- IRF9540N (P-Channel MOSFET)
- IRF540N (N-Channel MOSFET)
- SR160 Schottky diode (2 pcs)
- 680R resistor
- 50k potentiometer
- 4.7k resistor
- Solar Panel 15-18V with more than 300mA current rating (if using a 3600mAh battery)
- Wires for connecting solar panel and LEDs
- Hookup wires
Once you have gathered the components, follow the circuit diagram to construct the solar garden light on a breadboard.
Solar Garden Light Testing
To test the solar garden light, use a 10W solar panel with an 18V output. Place the solar panel in direct sunlight during peak solar conditions. Adjust the potentiometer to achieve 8.5V across D2. This voltage corresponds to the charging voltage, as a fully charged lithium battery reaches 8.4V.
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During the charging process, use an ammeter in series with the battery to check the charge current. The current will vary depending on solar conditions, increasing on sunny days and decreasing on cloudy days.
At night, when the solar panel receives no radiation, the battery will stop charging, and the LED lights will turn on automatically. You can watch a demonstration of the light turning on without radiation in the video provided.
Frequently Asked Questions
Q: Can I use a different type of battery for this project?
A: We recommend using a 7.4V lithium battery with built-in protection for safety. If you choose a different battery, ensure it has the necessary protective features or use an external protection module.
Q: What is the estimated battery backup time for this project?
A: With the current configuration, the selected battery will light up the LEDs for approximately 5-6 hours under nominal charge conditions. You can increase the LED strings according to your needs.
Q: Can I improve the circuit further?
A: This circuit is a basic lithium battery charger circuit for a simple garden light project. For proper charging and implementing a maximum power point tracker (MPPT), dedicated driver ICs can be used. Additionally, it is essential to use a proper PCB and an enclosed waterproof box for outdoor operation.
Now that you have learned how to create your own solar garden light, have fun implementing this project and enjoy the beauty of your garden even at night! For any modifications or further discussions, feel free to join the active forum at Circuit Digest.
