Solar energy is clean and limitless, and the operational costs are close to nothing once you’ve installed a solar panel as no fuel is needed to create a considerable amount of energy. And a single kerosene wick burns an estimated 80 liters of fuel, producing more than 250 kilograms of carbon dioxide per year.
To help people living in remote places with limited access to electricity, we made a low-cost solar light bulb as a replacement for a harmful kerosene lamp.
I have already posted an Instructable on this project. The earlier version is quite popular on the internet and useful for people all around the globe. So, I thought to redesign the lamp.
In this article, I will share the entire design process of my DIY solar lamp ( PCB Design, Enclosure Design, and Assembling).
This project was presented at AU 2020 conference, you can watch the full video.
Benefits:
1.Use of the solar lamp will decrease the amount of local air pollution and saves energy.
2. It also came out as an alternative business model with the potential to strengthen the overall rural economy by generating technology-based livelihood opportunities.
3. It can provide access to solar lamps at an affordable price to a wide range of audiences living in remote villages that are deprived of clean energy access.
Supplies:
1. Solar Panel -2V ( Amazon )
2. IC QX5252F ( Amazon )
3. 33uH Inductor ( Amazon )
4. 8mm Straw Hat LED ( Amazon )
5. Switch ( Aliexpress )
6. DC Jack ( Amazon )
7. AA NiMh Battery ( Amazon )
8. Battery Spring Plates ( Amazon )
9. 22 AWG wires ( Amazon )
10. Heatshrink Tubing ( Amazon )
10. JST male-female connectors ( Amazon )
11. PCB ( PCBWay)
12. 1W Solar Panel ( 3 – 5V ) ( Amazon )
13. Spray Paint – Bright Chrome ( Amazon )
Tools Used
1. Soldering Iron ( Amazon )
2. Wire Stripper ( Amazon )
3.Nipper ( Amazon )
4. Hot Air Gun ( Amazon )
5. 3D Printer ( Amazon )
Components of Solar Lamp
The solar lamp is a standalone SPV system and contains four components of a Standalone SPV system:
1.Solar Panel: Convert Solar Energy to Electrical Energy
2.Controller: Charge the Battery ( Charger ) and drive the Load ( Driver )
3.Battery: Store the Electrical Energy
4.Load (LED): Provide the desired light output
Controller Selection
The controller has two tasks
1. Charging the Battery:
Isolate the Solar Panel and Battery when the battery is fully charged and Isolate the load from the battery when the battery voltage is low.
2. Driving the LED:
Capable to drive the selected LED ( ability to handle the required voltage and current ) i.e Boost the battery voltage ( 1.2V ) to LED operating voltage (3.2V) or higher
Here we will use a cheap QX5252F IC as a controller.
The main features are:
1.Suitable for a single AA NiMh/NiCd battery
2.Operating Voltage: 0.9V-1.5V
3.Output current: 3mA-300mA ( Our requirement is 93.7mA )
4.Integrated Schottky Diode
5.High Efficiency up to 84%
6.Low quiescent current: 17uA ( When the circuit is not working / standby )
7.Only an external inductor is required for making the Circuit
How the Circuit Works?
The heart of this Solar Lamp is a very small 4 legged IC QX5252F. It works similar to the “Joule Thief ” circuit. But the advantage of using this chip is that it does not require a bulky and heavy toroid. It does the same job using only a simple inductor, a single AA / AAA battery, and a LED.
It requires only an external inductor for making the Circuit. The LED current can be changed by using a different value inductor. The chart is shown in the above picture. I have used a 33uH inductor.
Connection :
Pin-1 -> Solar panel positive terminal
Pin-2 -> Battery positive terminal and one leg of Inductor
Pin-3 -> All ground ( Solar panel, Battery, and LED negative terminal)
Pin-4 -> Another leg of Inductor
Breadboard Testing
Before finalizing the circuit, It is always a good idea to prototype the circuit on a breadboard. This lets you check to make sure that all of your components are working perfectly.
Make the circuit on your bread bard as per the schematic. The LED should not glow if the circuit is correct. To simulate the dark condition, cover the solar panel with your palm. Now the LED should glow.
PCB Design
I have drawn the schematic by using EasyEDA online software after that switched to PCB layout.
All of the components you added in the schematic should be there, stacked on top of each other, ready to be placed and routed. Drag the components by grabbing on its pads. Then place it inside the rectangular borderline.
Arrange all the components in such a way that the board occupies minimum space. The smaller the board size, the cheaper will be the PCB manufacturing cost. It will be useful if this board has some mounting holes on it so that it can be mounted in an enclosure.
Now you have to route. Routing is the most fun part of this entire process. It’s like solving a puzzle! Using the tracking tool we need to connect all the components. You can use both the top and the bottom layer for avoiding overlap between two different tracks and making the tracks shorter.
You can use the Silk layer to add text to the board. Also, we are able to insert an image file, so I add an image of my website logo to be printed on the board. In the end, using the copper area tool, we need to create the ground area of the PCB.
Now the PCB is ready for manufacturing.
You can order it from PCBWaySign up PCBWay now to get a US $5 coupon. That means your first order is free of cost only you have to pay the shipping charges.
When you place an order, I will get 10% donation from PCBWay for contribution to my work. Your little help may encourage me to do more awesome work in the future. Thank you for your cooperation.
Solder the Components
It is good practice to solder the components according to their height. Solder the lesser height components first. You can follow the following steps to solder the components :
1. Push the component legs through their holes, and turn the PCB on its back.
2. Hold the tip of the soldering iron to the junction of the pad and the leg of the component.
3. Feed solder into the joint so that it flows all around the lead and covers the pad. Once it has flowed all around, move the tip away.
First I have soldered the inductor, then the two JST connectors, and QX5252F.
Solder the Inductor
Inductor comes in various packages, but here I have used an axial Inductor with a value of 33uH / 0.5W.
First bend the two legs at a right angle, then push the legs through the holes named “L” on the PCB.
Solder the inductor legs to the soldering pads on the PCB.
Solder the QX5252F
The QX5252F comes in TO-94 package, the space between the adjacent legs is very small. So extra care must be taken during soldering. Otherwise, you will short the pins together.
In my V2.0 PCB, I have used the TO-94 package footprint, but in V3.0 I have used a wider footprint so that less chance of a short circuit between the two legs.
Insert the QX5252F legs into the PCB holes, to insert correctly, number-1 is marked on the PCB. The pinout of the QX5252F chip is shown above.
Solder the JST Connectors
Two JST connectors are used for connecting the terminal wires from the battery and solar panel.
Here I have used JST 2.0 PH, during buying be sure you are selecting the right components.
Insert the two JST connectors into the holes named “SOL” and “BAT”, then solder them.
Before soldering, be sure that the connectors are inserted correctly ( polarity is correct ).
Solder the LED
The LED used in this project is an 8mm / 0.5W straw hat type.
I have soldered the LED on the backside of the PCB. The reason for soldering the LED on the backside is that it will be easier to mount into the Front Reflector. But if you are not planning to use a 3D printed enclosure, you can solder the LED on the front side. Solder the LED with correct polarity, the longer leg of the LED is always a positive terminal. Then trim the extra legs by using a nipper.
Prepare the External Components
The external components are Solar Panel, DC Jack, battery spring plates, and rocker switch.
First, solder the JST connector terminal wire to the solar panel. The red wire will be connected to the positive and the black wire to the negative terminal.
Similarly, connect another JST connector to the two battery contact plates. The spring shape contact is the negative terminal.
At last, connect terminal wires to the DC jack and rocker switch.
Note:
1. Apply a small amount of soldering flux before soldering.
2. Apply heat shrink tubing to the exposed soldering joints, to avoid any accidental short circuit.
3D Printed Enclosure Design
To give a nice commercial product look, my friend ” VARUN” has designed this enclosure for this project. He used Autodesk Fusion 360 to design the enclosure.
You can watch the AU2020 video ( 13:12), for steps by steps tutorial for this enclosure design.
The enclosure has two parts:
1. Main Body
2. Front Cover
The Main Body is basically designed to fit all the components including the battery. The front cover is to cover up the main body and serve as a reflector to spread the light from the LED.
Download the .STL files from Thingiverse.
Printing the Enclosure
I have used my Creality CR-10 Mini printer and 1.75 mm Green and White PLA filaments to print the parts. It took me about 5 hours to print the main body and around 2 hours to print the front reflector.
My settings are:
1. Print Speed: 60 mm/s
2. Layer Height: 0.2mm ( 0.3 also works well)
3. Fill Density: 25%
4. Extruder Temperature: 200 deg C
5. Bed Temp: 60 deg C
Preparing the Reflector
The reflector can be purchased directly from the market, but to reduce the cost, it is considered to be a part of the 3D-printed enclosure. Only you have to apply a few coats of reflective spray paint on the 3d printed enclosure.
Before applying the paint, cover the edges of the enclosure with masking tape, so that paint will be only applied to the reflector part.
Apply the spray paint over the enclosure surface. Then leave it for 10 -15 minutes to dry out. Repeat the same process 2 to 3 times (2-3 coats). It depends on you, how much smoothness you like.
After the final coat, leave it for 3-4 hours for complete drying.
Safety: Wear nose musk during the frosting. I will recommend doing it outside and well-ventilated space.
Install the Components
Install the Solar panel on the top of the enclosure. The solar panel that I used is 58 x58 mm. Then install the DC jack and rocker switch.
At last install the PCB on the front reflector. Use hot-glue to fix all the components with the 3D-printed enclosure. The enclosure is a snap-fit type, so we will not require additional mounting screws. Just align the tabs in the front reflector to the slots in the main body and then press it.
Finishing
To test the lamp, cover the solar panel with your palm, the LED should glow. If the LED lights up, then the circuit is working perfectly.
Before using the lamp, it is recommended to charge the battery in bright sunlight.
You can place the lamp outside or you can keep the lamp inside and use an external solar panel (4 to 5V) to charge the lamp.
Hope my solar light bulb will give light to many rural people around the globe.
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