• Skip to main content
  • Skip to primary sidebar

Homemade Circuit Projects

Get free circuit help 24/7

New Projects | Privacy Policy | About us | Contact | Disclaimer | Copyright | Videos 

You are here: Home / Mini Projects / Simple Solar Garden Light Circuit – With Automatic Cut Off

Simple Solar Garden Light Circuit – With Automatic Cut Off

Last Updated on August 25, 2022 by Swagatam 284 Comments

A very simple automatic solar light system for illuminating your garden passages can be built using some LEDs, a rechargeable battery and a small solar panel. The system automatically switches ON the lamps at dusk and switches them OFF at dawn.

How it Works

The circuit design is extremely straightforward and may be understood with the following points:

As can be seen in the given circuit diagram, the design basically consists of a solar panel, a PNP transistor, few LEDs, a battery and a few resistors.

The transistor is the only active component which is positioned as a switch for preventing the battery voltage from reaching the connected LEDs during day time.

During broad day light, the solar panel produces the required amount of voltage which is applied across the rechargeable battery via the 1N4007 diode and the resistor R*. This voltage charges the battery gradually from dawn to dusk.

Selecting the Current Limiter Resistor

The resistor R* value should be adjusted as per the specs of the battery for limiting excessive current to it.

The resistor also serves as the current limiting resistor for the connected LEDs when the transistor is switched ON.

Here it has been calculated as 10 Ohms.

As long as the solar panel generates the optimal amount of power, the positive potential at the base of the transistor keeps it switched OFF.

However when dusk sets in the solar voltage begins to drop, and when it drops below the zener diode rating, the transistor slowly starts conducting, illuminating the LEds gradually.

With complete absence of sun light or when its completely dark, the transistor conducts fully with the help of the 1K resistor, and produces full brightness over the LEDs.

The next morning, the cycle repeats all over again.

The circuit can be modified in many different ways.

Circuit Diagram

simple solar LED lamp circuit
caution electricity can be dangerous

The above diagram may also be built in the following manner. It looks more sensible now as the resistor is removed from the emitter for facilitating efficient triggering of the transistor.

PCB Design

solar garden light PCB design

Pictorial Diagram

Parts List

The diagram shows an incorrect transistor number (8050), use 8550 instead.

Recommended Solar Panel Specs

6 to 8V/2 watt

Voltage - 6V

Current - 330 mA

garden light solar panel

Using a 9 V Battery and High Bright White LED

The next shows an elaborate yet simple solar garden light diagram in pictorial form

R2 is the LED current limiting resistor which can be calculated using the following formula:

R2 = Battery Voltage - LED Fwd Voltage / LED Current

R3 is the charging current limiter resistor for the battery, and it can be calculated using the following formula:

R3 = Solar Panel Voltage - Battery Voltage / 10% of Battery mAH Rating

The battery voltage must be at least 3 V higher than LED voltage.

The panel voltage must be at least 3 V higher than the battery voltage.

Using NPN Transistors

The above explained designs can be also replicated using two NPN transistors as shown in the following diagram:

Solar Pathway Light Circuit with Constant Voltage

If a Li-Ion battery is intended to be used for the above explained circuit, a constant voltage feature becomes crucial for safeguarding battery life and prolonging it.

The following circuit show how this may be done by adding a simple voltage follower regulator circuit:

current controlled LED lamp circuit

If a 3.7V Li-Ion battery is used, make sure to adjust the 10K preset to achieve precisely 4V across the output points where the battery is supposed to be connected, do this adjustment without connecting the battery.

The 4V level ensures that the battery is never overcharged (at 4.2V) and this also allows the circuit charge the battery without a constant current supply.

1.5V Solar Garden Light with Enhanced Features

The following solar powered garden light was designed by Mr. Guido which includes additional features such over charge and low charge cut off for the battery and with  a Schmidt trigger.

This ensures that the connected battery is never allowed to charge or discharge beyond unsafe levels.

The main attraction of the circuit is the use of a single rechargeable AAA penlight cell, which is able to light up a 3.3V high bright LED through an attached Joule thief circuit.

solar LED lamp with auto cut off circuit

High Power 12V Garden Light Circuit

The following image shows a high power automatic garden porch light circuit using a 12V 7 Ah battery. The LEDs used are high power 1 watt LED each. Since 9 LEDs are used the total power output becomes 9 watt.

Please remember to connect a Diode between R1 and the battery positive.

The circuit is designed to automatically switch ON the LEDs when the darkness level drops sufficiently and the solar panel voltage drops below 3 V.

The LED series resistor values can be calculated using the following formula:

R = Battery Supply - LED FWD V Drop / LED Current

= 13 - (3.3 x 3) / 0.3

= 2.1 / 0.3 = 7 Ohms

Resistor wattage = 2.1 x 0.3 = 0.63 watts or 1 watt.

The solar panel can be rated at 18V, 3 amp. The battery specification is 12V, 7 Ah. The solar panel output voltage is regulated using the LM338 voltage regulator.

Make sure that the 5K pot of the LM338 circuit is precisely adjusted to produce 14V for charging the 12V battery.

You'll also like:

  • 1.  Simple Hi Efficiency LED Torch Circuit
  • 2.  MPPT vs Solar Tracker – Differences Explored
  • 3.  Convert SMPS into a Solar Charger
  • 4.  Simple Intercom Circuit [2 way]
  • 5.  Elementary Electronics Explained
  • 6.  PWM Solar Battery Charger Circuit

About Swagatam

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials.
If you have any circuit related query, you may interact through comments, I'll be most happy to help!

Have Questions? Please Comment below to Solve your Queries! Comments must be Related to the above Topic!!

Subscribe
Notify of
284 Comments
Newest
Oldest
Inline Feedbacks
View all comments

Primary Sidebar

Categories

  • 3-Phase Power (15)
  • 324 IC Circuits (19)
  • 4017 IC Circuits (52)
  • 4060 IC Circuits (26)
  • 555 IC Circuits (99)
  • 741 IC Circuits (20)
  • Arduino Engineering Projects (83)
  • Audio and Amplifier Projects (115)
  • Battery Chargers (83)
  • Car and Motorcycle (95)
  • Datasheets (74)
  • Decorative Lighting (Diwali, Christmas) (33)
  • Electronic Components (101)
  • Electronic Devices and Circuit Theory (36)
  • Electronics Tutorial (120)
  • Fish Aquarium (5)
  • Free Energy (34)
  • Fun Projects (13)
  • GSM Projects (9)
  • Health Related (20)
  • Heater Controllers (29)
  • Home Electrical Circuits (104)
  • How to Articles (20)
  • Incubator Related (6)
  • Industrial Electronics (28)
  • Infrared (IR) (40)
  • Inverter Circuits (98)
  • Laser Projects (12)
  • LED and Light Effect (93)
  • LM317/LM338 (21)
  • LM3915 IC (25)
  • Meters and Testers (66)
  • Mini Projects (150)
  • Motor Controller (67)
  • MPPT (7)
  • Oscillator Circuits (26)
  • PIR (Passive Infrared) (8)
  • Power Electronics (34)
  • Power Supply Circuits (79)
  • Radio Circuits (10)
  • Remote Control (48)
  • Security and Alarm (62)
  • Sensors and Detectors (121)
  • SG3525 IC (5)
  • Simple Circuits (75)
  • SMPS (29)
  • Solar Controllers (61)
  • Timer and Delay Relay (53)
  • TL494 IC (5)
  • Transformerless Power Supply (8)
  • Transmitter Circuits (41)
  • Ultrasonic Projects (16)
  • Water Level Controller (45)

Calculators

  • AWG to Millimeter Converter
  • Battery Back up Time Calculator
  • Capacitance Reactance Calculator
  • IC 555 Astable Calculator
  • IC 555 Monostable Calculator
  • Inductance Calculator
  • LC Resonance Calculator
  • LM317, LM338, LM396 Calculator
  • Ohm’s Law Calculator
  • Phase Angle Phase Shift Calculator
  • Power Factor (PF) Calculator
  • Reactance Calculator
  • Small Signal Transistor(BJT) and Diode Quick Datasheet
  • Transistor Astable Calculator
  • Transistor base Resistor Calculator
  • Voltage Divider Calculator
  • Wire Current Calculator
  • Zener Diode Calculator

© 2023 · Swagatam Innovations

wpDiscuz