Introduction: DIY Portable Solar Powerbank (w/ 110v Outlets & USB Ports)

This week we are building SlimPanel, an intelligent all-in-one solution for portable solar energy production. SlimPanel has all the needed components inside a portable 1 inch enclosure. Basically it's a huge but portable powerbank that can power 220v/110v appliances and USB devices. It uses an Arduino for its brains and can be upgraded to work with the Intel Edison IoT.


My reason for building this project is to develop and deliver a cheaper alternative for non-renewable energy. Yes the technology has been invented but the incorporation to fit everything you need inside the Solar Panel's enclosure is far from conventional. Rich or poor, people need electricity. The project aims to deliver electricity to areas that have no access to electricity. Other than that, the project can be of use to the consumer level. People can use it as a source of electricity wherever they choose to go. In my opinion, this is an important tool for survival.


This is our investigatory project for our physics class in High School. I'm planning to enter this for this year's Google Science fair and for Intel's science contest. The project is still in the making and I'm build several prototypes to reach perfection.


Here's teaser of my upcoming video tutorial:

It can power a 32" LCD TV and a Laptop too!


The project is still in the making. I'll be updating this guide frequently until I stop and decide to build the SlimPanel v2.0. Your opinion is what matters most to me, it helps a lot on building my version 2.0.


Step 1: Google Science Fair 2015 and Intel 2015 (Research Paper)

I'm joining this in several science fair contests. Hope I win same as last year.


Cool new high production video coming soon!

Step 2: Glossary - Words to Understand

Charge Controller -

Voltage Divider -

Battery Balancing -

Inverter -

Regulator -

Lithium Batteries -

Step 3: Layout of the Electronics - How It Works

Here's a block diagram of the project. I apologize for the poor quality, I've used MS Paint to make the diagram. Anyway, I wrote a layman's description below on how the system works. I wont use too much technical terms so that everyone would understand.

How It Works:

1st.) The solar panel converts sunlight to electricity during day.

2nd.) The power output of the solar panel goes through a junction going to a voltage divider. The voltage divider makes the output voltage below 5 volts making it readable to the Arduino MCU's analog pin. This voltage divider keeps track of the solar panel's output voltage.

3rd.) After passing through the junction of the voltage divider, the power output of the solar panel enters the charge controller section of the circuit.

4th.) The MCU runs an Algorithm to control the charging cycle of the charge controller.

5th.) After the solar panel's power output has passed through the charge controller (with the MCU's permission), it will then go through a junction to another voltage divider. The second voltage divider (this one) is used for getting the battery's voltage (used for power status).

6th.) After going passing through the voltage divider's junction, the panel's output now gets to charge the Li-ion battery pack.

7th.) The charging wont stop until the MCU has detected that the battery is full.

8th.) In addition, there's another line (parallel to the charger's charging line) that goes to the MOSFET load switcher. The load switcher is in charge of turning the appliances on and off automatically. It works very similar to relays. Again, the MCU has control to the load switcher. You can modify the program in step # 31 to add some cool new features to the SlimPanel.

9th.) The load switcher follows the written program. The default program will only supply electricity to the USB charger and Power Inverter if the battery has enough power (16v low cut-off). You can customize the MCU's program to add a menu selection.

10th.) The USB Charger regulates the output power of the battery and lowers it to 5V (2A). The output then goes to the modified USB HUB. The hub extends the number of ports.

11th.) The inverter converts the Regulated 12v to AC (220v), the power used for wall appliances.

12th.) While all of these are happening simultaneously, there are other modules that are also operating. Ones like the tact buttons (for control), LCD screen (for displaying the battery status and power modes, Bluetooth module (for smartphone control and telemetry) and WiFi module (Intel IoT).

Step 4: Gather the Parts & Materials

Here are the parts you'll need:

General Components:

- 12v to 220v Inverter

- 2A USB Charger

- 20W Solar Panel

- Arduino Uno

- LCD Screen

- USB Hub

- 18650 li-ion Battery

Discrete Components:

- ATmega328 IC (Included with Arduino)

- 28 Pin IC Socket (for Atmega328)

- 16mHz Crystal Oscillator

- 22pF Ceramic Capacitor



- 2N3904 NPN Transistor

- SPDT Switch


- AC Sockets

- Epoxy

- Super Glue

- Glue Sticks

- Silicone Sealant

Step 5: Might As Well Buy an Intel Edison (IoT)

The original plan was to build the project having the Edison as the MCU. I failed to do so since I'm lacking the compact breakout board for the Edison. I'm still planing to pursuit to use my original on the Version 2.0 of SlimPanel.

Step 6: Measure the Components

Grab your note pad and vernier caliper then write down the measurements.You'll be needing them later.

Step 7: Mark the Cutouts

Plan and layout the placement of parts then draw the acquired measurements to the solar panel's aluminum frame. Don't use ballpens or markers they will smuge, use pencil instead.

Step 8: Grind Some Metal!

You are probably wondering how were you suppose to cut the aluminum frame. The answer: you could use your electric drill and jigsaw. First, drill a hole for the buttons and a hole at the center of the rectangular markings. Next, useyour jigsaw to finish off the remaining metal from the rectangular markings. If you have access to a jigsaw, you can use a hacksaw or you can use a rotary tool.

Step 9: Smoothen the Edges

Use your metal file to smoothen the sharp edges. Do it slowly and patiently, there's no going back once you have filed too much metal.

Step 10: Hack the USB Hub

In this step, you'll be needing a USB hub. As much as possible, buy the cheapest one. Quality doesn't matter that much since we will be removing most of the components inside.


I used a USB hub to expand the number of USB ports of my USB car charger. You will need to hack your USB port to remove all the vampire components. The USB hub consumes electricity to power the IC that expands the ports, we wont be needing that since we are only tapping in the hub's power line. Once you are done desoldering the components, solder two hookup wires to the DC power jack.

Step 11: Hack & Acquire the USB Charger's Internals

Find a 12 USB charger with a 2.1 ampere output. Some mobile devices like the latest apple products only charge at 2.1A, they won't work with chargers rated below 2.1 amperes.


Find a way to dismantle the USB charger. You can open most of the cheap chargers by using a screw driver to push apart the plastic division. The expensive ones usually comes off by unscrewing the tip of the 12v plug's fuse area.

Step 12: Connect the Hub to the 12v USB Charger

Now, solder the wires of your hacked USB hub to your USB charger's USB port (note: I removed the female plug from the charger). Next, solder two hookup wires to the charger's 12v input.

Step 13: Mount the Hub to the Panel

Hot glue the USB hub together with the 12v charger's circuitry on the solar panel.

Step 14: Mount the AC Sockets

These AC sockets were supposed to be snap-ons although the double wall aluminum frame was too thick. The latches didn't work so I hot glued them too. For the wiring of the outlet, both of them are soldered in parallel.

Step 15: Disassemble the Inverter

I you happen to have a 12v inverter lying around, you can use it for the project. If you don't, you could buy one from eBay or Amazon. They don't cost that much, if you buy the right ones. Their price range lies around $5-$25. As much as possible, buy the 75W version, anything higher than that will consume too much electricity and will drain the battery faster.


When you happen to find or buy one, check it if it works and find if it's fit for your appliance's voltage. Next, dismantle the inverter to get the circuit inside. Be sure to exercise caution, some inverters contain charged capacitors that could cause electric shocks. You can dismantle the inverter by unscrewing the fuse head found at the tip of the 12v plug of your inverter.

Step 16: Connect the Sockets to the Inverter

The wires that you've soldered to the AC sockets can now be soldered to the AC output of the 12v inverter.

Step 17: Mount the LCD

I bought this cheap 8x1 character SPI LCD from e-Gizmo for P90 ($2.00). It was perfect since the LCD was able to fit within the solar panel's frame. You can mount it by simply using hot glue, same to the tact buttons.

Step 18: Mount the Buttons

Step 19: Do Some Outdoor Testing (Getting the Voltage)

Aside from using my solar panel's datasheet as reference, I thought it would be wise to do some testing to see if the values of the datasheet were accurate. It turns out that the solar panel's max (no load) voltage was 3v higher than the one specified in the datasheet. Acquiring the max voltage is very important, it dictates how the number of battery-cells your solar panel can charge. You will also need the max voltage later for constructing the voltage divider of the charge controller circuit later on.

Step 20: Build a Dual 12v Regulator

I plan to use 5 Li-ion cells connected in series. When connected in series, the batteries will yield a max voltage of 21v. The inverter and USB charger will only operate at voltages ranging from 11-14v. In order for us to use the appliances safely, we would have to regulate the supply that goes to the charger and inverter. In this project, I used and designed a linear regulator since I was not able to get hold of a Switching Regulator/ Buck Converter. This is a huge step down for me, although I'm still planning to replace this Linear regulator with a much more efficient switching regulator, if ever I get hold of one.


If ever you chose to build the linear regulator, you can download the zip file below. The zip file contains everything you need: the schematic diagram, the Printable PCB Layout (PDF) and the raw fritzing file.

Step 21: Assemble the Dual Regulator

In assembling the linear regulator, bend the transistor and regulator's pins facing forward. When you solder the tansistors and regulators, the metal (heatsink) portion must be facing upwards. Be sure to use a mylar insulator and plastic washer for the 7805 regulators and the TIP35C transistors. If you don't have one with you, you can simply cover the 7805 with a thick peice of masking tape (no need for the TIP35C transistors). Now screw both transistors to the heatsink, leaving the regulators unscrewed. The transistors do not need insulation since the metal plates are both connected to a common rail, the regulators on the other hand are connected to the opposite voltage of the rail so they need to be isolated from the heatsink. The regulators do not need to be screwed to the heatsink since they don't dissipate too much heat.

Step 22: A Better Alternative for the Regulator

If you are patient enough to wait for the shipping, I would suggest buying a buck converter. Buck converters are much more efficient than linear regulators.

Step 23: Connect the Regulator to the Other Components

Connect the output of the regulator to the inverter and to the 12v USB charger. Leave the input hanging. For now, I'm using epoxy to mount the heatsink. A smart suggestion would be to screw the heatsink directly to the Aluminum frame of the panel.

Step 24: Build the Charge Controller Circuit

This is the heart of the project. The charge controller controls everything. It regulates the voltage and current coming from your solar panels which is placed between a solar panel and a battery. It is used to maintain the proper charging voltage on the batteries. As the input voltage from the solar panel rises, the charge controller regulates the charge to the batteries preventing any over charging.


What's The Advantage of Building One Instead of Buying One?

Pre-made charge controllers are meant to work directly out of the box. Yes, a pre-manufactured controller is easier to use but it has its limitations and that would be the lack if customizability. The answer to that is to build a DIY Charge Controller, having an Arduino as its brain. We all know what Arduino's could do, pretty much anything I guess. If ever you'd want to set a different voltage cut-off, you can just program it with your laptop. If you would like to add other functions, you could program the it do do what you want as well.


I've acquired the circuit's design from my good friend, Debashish (Deba168). He has designed three outstanding solar charge controllers, here in instructables and I highly recommend his projects.


This guide won't explain the detailed process of building a charge controller since it is to broad to teach, instead you can visit these well documented instructables of Debashish (Deba168) on building one from scratch:




BTW, In this project, I used the charge controller design from the fist link.

Step 25: Add a Balancing Charger Circuit (Soon to Upgrade)

Recently, I got help from Adam Munich in designing a better charger (his design) for the SlimPanel project. The balancing charger is designed to charge Lithium batteries, Li-ion to be specific. It's designed to keep track of each Li-ion cell's voltage. I was not able to implement the balancing charger to my current version of SlimPanel since I was not able to get hold of the shipment in time. I'm planning to add it to my 2nd version of the project. Since lithium batteries are very sensitive to draining, a lithium balancing charger is recommended to prevent explosions. The balancing charger circuit makes sure that each lithium cell receives an equal charge distribution.

Step 26: Alternatives for the Controller

There's a wide variety to chose from. If you don't have enough experience to build an Arduino version, you can always choose to buy a ready made controller.

Here's a link to Amazon's top selling controllers: Solar Charge Controllers

Step 27: Assemble Li-ion the Battery Pack

Recently I found a store that sells lithium 18650 Lithium-Ion batteries for $2 each. Lithium batteries are the most efficient so far. They charge faster, have a higher current discharge rate, has great size to capacity ratio and is relatively cheap. Each cell rated at 3.7v (2000mAh). I soldered four of them in series to build a 14.8v (2000mAh) battery pack. Be sure to solder them fast, otherwise things could go wrong once you heat them up too long.


Advantages of Li-ion:

As seen on the graph above, Lithium-ion batteries have a sudden discharge characteristic. Unlike Lead Acid Batteries, they would still maintain the same voltage until the battery runs low.

Step 28: Hot Surface Battery Hazard (Fix)

Lithium Batteries are sensitive to heat, being exposed to extreme heat could cause explosions. The solar panel, when exposed under sunlight, could heat-up up to +100° C. My solution for this was too add a huge 12v snail fan to cool the the surface where the batteries are mounted on. The fan is connected directly to the solar panel. The fan will turn whenever the solar panel produces electricity from sunlight. There no need for temperature sensors, I'm against overkilling prototypes.

Step 29: Hook Them Up Together

Now that you have all the parts mounted within the solar panel's frame, you can now connect everything together. Just follow the block diagram.

Step 30: Construct the Back Panel

Cut a piece of foam board then use it to cover the rear area of the panel. You can either screw it or hot glue it to the solar panel's frame.

Step 31: Program It

Download the codes below.

Step 32: Demo - Video

SlimPanel - Powering a 32" LCD TV and a Laptop:

Project Teaser:

Step 33: Coming Next - SlimPanel (v2.0)

MAKE ENERGY: A US-Mexico Innovation Challenge

Second Prize in the
MAKE ENERGY: A US-Mexico Innovation Challenge

Explore Science Contest

Participated in the
Explore Science Contest

Guerilla Design Contest

Participated in the
Guerilla Design Contest

Apocalypse Preparedness Contest

Participated in the
Apocalypse Preparedness Contest