Here we explain a really cheap and super simple solar pocket LED light circuit. This is not for fancy people, this is for poor folks, tribal people, village kids, who need cheap light at night to read, cook, and work.
The idea is small, compact, cheap and can run for years but then when the battery dies, we can replace it, not like those costly LED lights that go to waste after two to three years. This one is ethical, useful and practical.
This idea was given by Mr. Williams Hayward and we are making it real here, ok?
What We Need This Light To Do? – Our Plan, No Confusion!
We want to build a solar pocket LED light using a tiny plastic box (9cm x 5cm x 3cm, cost Rs.3/-). The light will have:
1W LED or multiple 20mA LEDs for good brightness
4V 1A rechargeable sealed lead-acid battery (brand like SUNCA, VICTARI)
Solar charging, but also a mobile charger option (for places where grid electricity is available)
Battery must be replaceable after two to three years (unlike costly LED lights that become useless when the battery dies)
This is meant for tribal or rural children who need a cheap way to light up a book at night. Yes expensive ones exist—like d.light (Rs.500) and Thrive (Rs.200) but they are badly designed. They work great but then when their battery cannot be replaced so after two to three years, the whole unit becomes junk. That is a waste of resources and unethical.
We need something cheaper (Rs.100-150) where the battery is easily available and replaceable. This will be sold non-profit through NGOs in tribal areas. Later we can even supply kits to village youth so they can assemble them locally and earn some money.
We Already Tested Something Similar – It Works!
Me and a colleague already made some test models:
Using a 7V EW high-power battery + 2x20mA Pirahna LEDs – It worked for 30+ hours, bright enough to read a book from half a meter away.
Using a 4V SUNCA battery + 1W 350mA LED – Gave enough light for cooking inside a hut.
So the idea works but now we want something even smaller and cheaper.
Now Can We Make It Even Simpler?
Now here is the challenge – Can we make this using just:
One AA or AAA rechargeable battery
A mini solar panel (must fit inside a 9cm x 5cm box lid)
A DC-DC booster circuit
20mA LEDs
Then when you need me to meet and discuss, I can come over, but for now, let us look at the circuit design, ok?
The Circuit Design – Super Simple, Just Works!
Since we need a tiny, powerful, and low-cost solar pocket LED light, here is what we do:
We use a single AAA 1.5V cell.
We boost the voltage using a Joule Thief circuit.
We charge it using a self-regulating solar charger.
Now let us see how the circuit works.
How The Joule Thief Circuit Works?
This is a basic step-up voltage circuit. Here we take a single 1.5V battery and use a BJT transistor + inductor to boost it up so it can power a 3.3V LED.
In the design we use a 1W LED but then if needed we can use a smaller 30mA high-bright LED.
This circuit extracts the last bit of energy from the battery, that is why it is called a Joule Thief.
But then since we use a rechargeable battery, we should not discharge it below 1V or the battery will die early.
Circuit Diagram
How The Solar Charging Circuit Works?
Now, we need to charge the AAA battery from the sun so we use a simple transistor-based charger.
The charging circuit is made using a low-power BJT.
It works as an emitter follower—whatever voltage we set at the base, the emitter follows it.
We set it using a 1K preset so the output never crosses 1.8V preventing overcharging.
The solar panel gives more than 3V, but the circuit limits charging to 1.8V max.
Then when the battery reaches full charge, the circuit automatically stops charging, preventing damage.
What About The Inductor?
The inductor is a small ferrite ring transformer.
It has 20:20 turns but we can adjust it to get the best voltage output.
The LED will keep working even when the battery drops below 1.2V.
Final Words – This Works, Just Follow The Steps!
So now we have a small, cheap, and powerful solar pocket LED light that can:
- Run on a single rechargeable AAA battery
- Charge from a small solar panel
- Boost the voltage to light up a 3.3V LED
- Run until the battery is almost dead
- Prevent overcharging then when full
- Battery can be replaced then when it dies
This is exactly what poor people need—cheap, reliable light that lasts! Just build it as explained, test it, and use it.
How to Build
How To Build This Solar Pocket LED Light – Step By Step, No Confusion
Alright, now here we will build this solar pocket LED light. No fancy tools, no complex stuff—just follow step by step and it will work perfectly, ok?
Step 1 – Collect All The Parts First, Do Not Skip Anything
First we need all the correct parts before we start soldering. Here is the full list.
Main Components
1.5V AAA or AA rechargeable battery – This is our power source.
3V, 200mA solar panel – This will charge the battery using sunlight.
1W white LED (or 20mA LED) – This is our light source.
Transistors
2N2222 (NPN BJT) – This is used in the Joule Thief circuit.
Any 200mA NPN BJT (BC547, BC548, etc.) – This is for the solar charging circuit.
Other Small Parts
1K resistor (two pieces) – Used for controlling current.
470-ohm resistor – Limits charging current from the solar panel.
100µF capacitor (optional, for better stability) – Helps smooth the circuit operation.
1N4148 diode – Prevents reverse current leakage.
Inductor – The Heart of the Joule Thief
Ferrite ring core (T13 size is good) – This is where we will wind the coil.
20:20 turns of 7/36 insulated copper wire – This makes the transformer for voltage boosting.
Step 2 – Build The Inductor First, Then Everything Else
Making The Inductor (Joule Thief Transformer)
Now here we need to make the coil carefully because if we mess this up, the circuit will not work.
Take the ferrite ring core (T13 or similar).
Use 7/36 insulated copper wire (thin wire).
Wind 20 turns on one side – This is the primary coil.
Wind another 20 turns on the same core – This is the secondary coil.
Make sure to twist and connect one end from each coil together – This becomes the center tap.
Scrape off the insulation at the ends so the copper is exposed for soldering.
Step 3 – Solder The Joule Thief Circuit First, Test If It Works
Now we build the main LED driver circuit.
Solder the 2N2222 transistor to the board.
Connect the center tap of the inductor to the collector of 2N2222.
Connect one side of the inductor to the positive of the battery.
Connect the other inductor side to the base of 2N2222 through a 1K resistor.
Now connect the emitter of 2N2222 to battery negative.
Solder the 1N4148 diode between the base and emitter.
Now connect the LED between collector and negative.
At this point test by connecting the battery—the LED should glow. Then when it does not glow check all connections again.
Step 4 – Build The Solar Charger Circuit
Now we add the solar charging circuit so the battery can charge in sunlight.
Solder the second transistor (any 200mA BJT) to the board.
Connect a 470-ohm resistor to the base of this transistor.
Connect the other side of this resistor to the solar panel positive.
Connect the collector of this transistor to battery positive.
Connect the emitter to battery negative.
Solder a 1K resistor across the base and emitter.
Now when the sun shines, the battery will charge automatically, and then when it is full, charging will stop automatically.
Step 5 – Assemble Everything Inside The Box
Now we put everything inside the small plastic box (9cm x 5cm x 3cm).
Fix the solar panel on the top lid – Make a small hole for wires.
Place the circuit board inside – Fix it properly with glue or screws.
Secure the battery inside – Make sure it can be removed and replaced.
Drill a hole for the LED – So it can shine outside.
Connect all wires properly and close the box.
Step 6 – Final Testing
Test the LED with the battery – It should glow bright.
Put the box in sunlight – The solar panel should charge the battery.
Check if the LED still works at night – It should glow even after hours.
Then when everything works fine, it means the project is successful.
Final Notes – Some Important Tips
Battery must be rechargeable – Do not use normal non-rechargeable batteries or it will not charge.
Solar panel must get full sunlight – Place it under direct sun for good charging.
LED brightness depends on inductor winding – Then when it is dim, try adjusting the coil turns.
Keep battery connections easy to replace – So then when it dies, anyone can swap a new one.
That is It, The Solar Pocket LED Light Is Ready
Now you have a cheap, simple, and working solar pocket LED light that anyone can build, use and even sell. This is perfect for villages, poor families, and rural students who need a long-lasting, replaceable light source.
Then when you have any problems, just check all steps again carefully and it will work.
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