Introduction: Green Power Bank to Help Save the Planet ! (Simplified Version)

Imagine a world where we never have to recharge our smartphones from the grid but instead could do it from a true renewable source of energy. A small gesture at the individual level but at the planetary level it could make a significant contribution. Furthermore, this (almost) daily ritual could serve as a reminder for each one of us that we can help in some way. This was the basic premise of this project when I embarked on it a few months ago. After multiple iterations I present to you via this Instructables the latest version (Simplified) of the "Green Power Bank". Thanks to suggestions from Instructables’ readers and a colleague teacher, this version is easier to build, needs less components, and works just as well. I hope that others will help improve the design and maybe see its multiplication around the world for convenience and for the good of humanity.


To be honest, the very first version I built was useless (not enough power to charge the batteries) and a serious fire hazard (no protection for parallel configuration of batteries, soldering connections directly on the batteries and, direct contact between an extremely hot solar panel and the batteries). After reviewing multiple comments and videos from the web I improved the a number of times design to make it easy to build and safe to operate. Here are a few benefits of the simplified version presented in this Instructables:

- Can use different 6-volt solar panel configurations as long as the total power does not exceed 5 watts (around 800 mA).

- Economical to build, especially if multiple units are produced (as some parts are not sold individually).

- Gives a second life to 18650 batteries coming from a dead laptop battery pack (see other Instructables to learn how).

- Leverages a battery holder for easy installation and avoid altering the batteries' characteristics through direct soldering.

- Leverages a low-cost DIY kit to give the project a professional look.

- Offers the possibility to keep the Power Bank at safe temperature (in the shade) while the solar panel gets very hot when directly exposed to the sun.

- Offers up to three levels of protection (built into the electronic board, glass fuses, PTC or thermal fuses).

- The solar panel can be detached from the Power Bank; the latter, in turn, can be used as an LED flashlight.


- While this simplified version is easier to built than the original version posted in Instructables and requires less parts, there are a number of limitations to consider. First it appears that you cannot charge the power bank via the solar panel simultaneously with charging a smartphone via one of the USB ports. Furthermore, the fact that the energy coming from the solar panel charge the batteries via the micro-USB port and thus a different part of the circuit on the board appears to impose more restrictions on acceptable minimum and maximum voltage coming from the solar panel (which is dependent on the ambient solar condition). But other than that everything works just fine.


To build this

project you will need:

1 X DIY Solar Power Bank Kit

1 X Solar Panel (6 volts, maximum 5 watts... around 800 mA in full sun)

1 X 5.5x2.1mm Female Jack to Micro USB Male Plug DC Power Connector Adapter

1 X Battery Holder (for 3 x 18650 batteries)

3 X Glass Fuses (1 amp.)

1 X 1N4002 Diode

3 X PTC Fuses (1.5 amp.) OR Thermal Fuse Cutoff (84 degree C or less if you can find it)

3 X 18650 Batteries (minimum 2200 mAh each... new or recycled from old laptop battery)

1 X Plastic Sheet (can use plastic from recycled vinegar or windshield washer fluid container... 2-7/8 X 4-1/2 inches)

10 inches of 22 AWG double wire (red/black)

5 feet of 16 AWG double wire (speaker cable)

ELECTRONIC BOARD SPECIFICATIONS (According to a supplier on AliExpress... Could not find anything else)

-Input (micro USB): 5 volts at around 1.5 amps. We use a 5-volt solar panel with a DC connector to micro USB adapter.

-Outputs (USBs): 5 volts at around 1 amp and 5 volts at around 2 amps.

-Battery: Suitable for polymer rechargeable lithium battery... 3.7 to 4.2 volts.

-Built-in protection: Standalone CPU security system to protect your device from overload, overcharging, overheating, and short circuiting while charging.

Step 1: Acquire All the Necessary Parts

As it may take a while for all the parts to get to your door, you may want to order what you need as soon as you can... The solar panel you choose to use may already have a wire attached to it so you may not need to get the 5 feet of 16 AWG double wire from the parts list but I would recommend to use the latter as it guaranty that you won’t face excessive resistance between the panel and the Power Bank. You may decide to build an array of solar panels from what you already have on hand as long as the total configuration amounts to 6 volts and DOES NOT exceed 5 watts (around 800 mA).

Step 2: Install the Electronic Board, On/Off Button, and Charge Status LED Diffuser

a) Insert the charge status LED diffuser in the appropriate four holes from the inside of the case. Add a drop of super glue to fix it in place permanently. If your version of the DIY kit does not have 2 small holes and pins to properly align the diffuser, make sure that how you install it (top versus bottom) won't interfere with the installation of the electronic board which will follow.

b) Insert the On/Off button in the appropriate hole from the inside of the case.

c) Make sure that the LED mounted on the electronic board is pointing forward like the USB connectors and is not bent downward during transportation. Adjust if necessary.

*** For the next step you will need to be patient and careful not to break the electronic board... Take your time ***

d) Insert the electronic board forward at an angle (see photo) making sure that the board LED is inside the appropriate hole. Make sure that the On/Off button is still in its hole.

e) With both hands, gently pry open both sides of the case (top side up) while your two thumbs push the electronic board downward and forward at the same time. There is a very specific place for it to sit and when it will be in place you will know for sure. You may want to have a look at the case and the board before you start to make sure you understand how it will sit once you have completed the task. Again, be patient... :-)

Step 3: Create a Plastic Sheet, Prepare the Lower Cover and Install It

Since we won't use the small solar panel that is provided with the DIY kit we will need to create a plastic sheet to replace it and install it on the bottom side of the Green Power Bank. In this example I used an empty vinegar container, but a car windshield washer container works just as well. Consistent with the green mission of this project, we are re-using part of a container and the rest can be recycled.

a) Empty the plastic container, clean it and cut the top and bottom parts (to be recycled).

b) Remove the label (you may need lighter fuel to remove some of the remaining glue).

c) Cut the middle part so you end up with a long sheet of plastic and draw a straight line on the top.

d) Trace a line along the bottom of the long plastic sheet so the height will be the same as the small sheet that is provided with the DIY kit.

e) Cut the top and bottom parts and separate the long sheet in multiple smaller sheets with identical dimensions as the one provided in the DIY kit (you may want to center any folds as you cut your sheets).

f) Make sure that the one sheet that you will use for this project fits nicely in one of the aluminum covers. If too tight, trim accordingly.

g) Install the newly created plastic sheet in the cover, then use four tiny screws to install the lower cover to the Power Bank case. Please take your time as if you make a mistake, removing those small screws is almost mission impossible !!

*** Do not worry if the plastic sheet is loose after you have screwed the lower cover. It will be resolved in one of the upcoming steps. ***

Step 4: Prepare the Electronic Board Solder Pads

a) Prepare the electronic board for connections by adding solder to four of the six connecting pads (B+, B-, Led+, Led-). You look for shiny bubble of solder on each one of them. Pay attention to the B- pad (for battery negative). You will see that a small surface mounted resistor is attached to it. Try to place the tip of your iron away from it when you touch the pad to avoid damaging it. Many people experienced problems with this small component according to the web.

Step 5: Install the LED Panel

a) Cut a 2-1/4 in. piece of 22 AWG double-wire.

b) Separate the red and black wires.

c) Skin about 1/8 in. at both ends of each wire, twist the four tips and cover with solder.

d) I recommend you test the LED panel before proceeding to make sure that it is functional and that the "+" and "-" indications are accurate. I have seen those being inverted. You may also want to write a "+" and "-" on the back of the panel to help making sure that the right wire will be going to the right place.

e) From the back of the panel, insert one end of the red wire into the "+" hole and one end of the black wire into the "-" hole.

f) Flip the board around, bend the two pieces of wire coming out of the two holes at about 45 degrees.

g) Solder both wires to the panel and remove exceeding length with cutting pliers.

h) Solder the other end of the red wire to the LED+ pad of the electronic board; solder the other end of the black wire to the LED- pad of the electronic board (see photos).

Step 6: Prepare the Battery Holder

*** Your battery holder might have a different configuration than what you will find here. The objective is that the three negative ends of the batteries are connected together and that a single black wire connects to the electronic board. As for the positive side, the three batteries need to be separated from one another as we will add 2 types of fuses to each one of them before joining them together and connecting to the electronic board. ***


a) If there is already a black wire connected to one of the three (-) terminals, remove it as it is likely too short.

b) Use one side of a 1/2 watt resistor to connect the (-) terminals which are not already connected.

c) Cut a 7 in. piece of 22 AWG double-wire, separate the two wires and put the red one away for future use.

d) Strip 1/4 in. at one end of the black wire and 1/8 in. at the other end. Twist and add solder to both ends.

e) Solder the 1/4 in. end to the (-) terminals (see photos).

f) Set a multimeter on "ohm" and verify that you read '0' between the end of the black wire and each one of the three (-) terminals.


a) If there is already a red wire connected to one of the three (+) terminals, remove it as we don't need it.

b) Cut any connections between the three (+) terminals (see photos).

c) Drill a small hole on the right side of each one of the three (+) terminals (when looking from the inside out... see photos). I used a 5/64 in. drill bit.

d) Add some solder on the top of each one of the three (+) terminals. Make sure that it does not fall down on the connector as it will cause improper connection when you add the batteries. This is a bit challenging as you don't want the plastic of the holder to melt but you don't want a cold solder (not shiny) either. Also, you need to pay attention to the iron as it might melt the plastic of the holder while you are focusing on adding solder on the terminals (yep... have a look at the photo... proper shiny solders but not very proud of what I did to the plastic in the process... Again, the antidote to this is to take your time and think of what you are about to do / doing... I failed on this one :-)

Step 7: Prepare the Batteries

a) Select three 18650 batteries with matching characteristics (as much as possible). If they are coming from dead laptop battery packs (see other Instructables to know how to salvage good batteries from dead laptop battery packs) make sure they all come from the same pack. Use the most powerful batteries that you can get but for an iPhone 7 you need a minimum of 2200-2300 mAh. batteries.

b) Use a multi-meter to make sure that the three thermal fuses won't induce any resistance to the project. This is crucial as otherwise the Power Bank might not work appropriately.

c) Use regular household scotch tape to attach the three thermal fuses to the three batteries. (About 1/4 inch from the top. If you have written the characteristics of your batteries on them you may want to install the fuses just above the handwriting as per the photos included... You will see why at the next step...).

Step 8: Assemble the Battery Pack

a) Slip in the three batteries in the holder while making sure that the right lead of each thermal fuse goes through the three holes that you just drilled. Rotate the batteries so the thermal fuses go as far down as possible on the right side of each battery. This way your handwriting will be on top and the battery pack will be as thin as possible (see photos).

b) Cut the three other leads of the thermal fuses and solder them to their respective battery connectors. You need to be efficient for this step as the batteries are already in the holder touching the connectors. To avoid transferring too much heat to the batteries your operation must take place fairly rapidly. One way to do it is to add some solder to what you already put on in the previous step while the thermal fuse lead is in position.

c) Use a multi-meter to measure the voltage between the black (-) wire and each one of the three leads coming out of the holder. I recommend that you fully charge the batteries before you start the project... You should thus read around 4 volts for each battery.

d) Add one strip of regular household scotch tape all around the battery pack in the middle of the batteries to make sure that they will stay in place during normal usage.

*** IMPORTANT NOTE ***It is imperative that the three batteries, which are mounted in a parallel configuration, be connected to each other via three individual fuses. Skipping this step would create a situation where if one of the batteries was to develop an internal short, the other two would instantly dump their respective energy in the failing one... thus generating a huge amount of heat and creating a serious fire hazard. With the configuration found here, the sudden surge of current would burn one or multiple fuses and immediately stop the flow of current to the failing battery. Do not skip the following steps.

e) Use a multi-meter to make sure that the three glass fuses won't induce any resistance to the project. This is crucial as otherwise the Power Bank might not work appropriately.

f) Twist one side of the three glass fuses together and solder them together (see photos).

g) Again, use a multi-meter to make sure that the three glass fuses won't induce any resistance to the project and that they did not go open circuit during the soldering process (should still read 0 ohm from one side to the other for each fuse... see photos).

h) With your fingers (no tool required) bend the leads that you just soldered together about 90 degrees from the glass fuses themselves (see photos).

i) Cut the three thermal fuse leads coming out of the holder, leaving about 1/8 in. and fold them upward. This creates three little hooks.

j) Put the battery pack inside the Power Bank, center it from a width's perspective and move it forward as far as you can until the holder touches the electronic board. With a marker, put a dot on the side of the battery holder in line with the B+ soldering pad of the electronic board (width and depth).

k) Pull out the battery pack and install the glass fuses assembly as per the photos. Start with the one on the right (when seen from the top) and make sure that the other side of the fuses (the three leads soldered together) is aligned with the dot you just drew on the holder.

l) You may want to use the multi-meter one last time and measure the voltage between the black (-) wire and the output of the battery pack (the 3 leads soldered together). Again, you should read around 4 volts.

Step 9: Install the Battery Pack Inside the Power Bank

*** IMPORTANT NOTE *** You now have a live and fully charged battery pack which is going into the Power Bank case. From this point on, you need to proceed with care to avoid any shorts or unwanted connections...I blew up glass fuses at this point... frustrating as you have to go back and replace them :-(

a) Put a few strips of double-sided household scotch tape on the back of the battery holder.

b) Important step: gently bend upward the leads from the glass fuses (the three soldered together) and cut what appears to be excessive length when considering that it will be soldered to the B+ pad on the electronic board. At this point it must not touch the pad !!! This is the very last connection we will make to the electronic board.

c) If the plastic sheet at the bottom of the case is loose (mentioned in a previous step), now is the time to solidify it... slide it towards the back of the Power Bank until it stops moving. Hold it there.

d) Insert the battery pack in the case making sure that it is centered from a width perspective and the side where the glass fuses are located actually touch the electronic board. If done right, the double-sided scotch tape must prevent the plastic sheet from moving while the holder is firmly in position and touching the electronic board.

e) While this is not very elegant, this next step will add a lot of strength to your Power Bank and prevent any movement inside the case during normal operation/travel or if it is dropped (yep... done that too). Use a hot glue gun and put a good amount on both sides of the case so the glue touches the holder, the plastic sheet at the bottom and the case on the side. Don't go all the way though to avoid any glue from touching the electronic board (see photos).

f) Flip the LED panel on top of the batteries and solder the black wire coming from the battery pack to the B- pad of the electronic board. Again, pay attention to your iron. You don't want to create a short or burn/melt anything at this point.

g) The moment of truth... Push the three leads (soldered together) coming from the glass fuses downward and solder them to the B+ pad of the electronic board. At this point, your Power Bank is alive and you should see some blue LEDs go on and then off. Ignore those indications for now.

Step 10: Position the LED Panel, Prepare and Install the Top Cover

a) Place the LED panel on top of the battery pack where you believe it should go and put the aluminum cover in its place (without the plastic sheet... Don't screw it on yet !).

b) With your fingers gently move the LED panel so it is well centered within the hole of the aluminum cover.

c) While holding the LED panel in place with your fingers, remove the aluminum cover and write four small marks in the four corners of the panel on the Power Bank case (see photos).

d) Put a few strips of double-sided scotch tape on the edge of the battery holder and on top of the three batteries.

e) Install the plastic sheet inside the top aluminum cover (centered) and put two pieces of double-sided scotch tape at both ends to hold it in place.

f) Put the LED panel in its final position by leveraging the four marks you drew on the case. The double-sided scotch tape should hold it in place.

g) Install the top cover and add the four little screws which were provided with the DIY kit.

h) Congratulations!!! You Power Bank is complete!!

Step 11: Test the Power Bank (Can Also Be Seen As the Operating Instructions)

a) As you probably know by now, there are two ways to charge your Power Bank... 1- via a micro-USB connector attached to an electrical outlet or 2- via a micro-USB connector attached to a solar panel. The very first step of this testing procedure is to plug-in an electrical outlet micro-USB charger as per the photo. The four charge level LEDs will turn on alternatively from left to right to show you the current level of charge and that it is in fact charging the Power Bank. Once fully charged all four LEDs will be ON solid.

*** VERY IMPORTANT POINT *** The reason why this is the first test is that plugging-in an electrical outlet micro-USB cable appears to reset the electronic board of any non-desired conditions. Please keep this in mind so that if your Power Bank ever demonstrates strange behavior, the first thing to do will be to charge it via an electrical outlet micro-USB connection.

b) Unplug the micro-USB cable.

c) Press the On/Off button once... The appropriate number of charge status LEDs will turn on for about seven seconds to let you know the level of charge of the Power Bank (1 LED= 1/4 charged, 2 LEDs = 1/2 charged, 3 LEDs = 3/4 charged, 4 LEDs = fully charged) and will then turn OFF on their own.

d) Quickly press the On/Off button twice... The ultraviolet LED (not sure why one would need this feature ??) turns ON... Quickly press the On/Off button twice again and the ultraviolet LED will turn OFF (see photo).

e) Press the On/Off button for about three seconds and the LED Panel will activate... in high intensity...

While the LED Panel is activated: A quick press of the On/Off button will toggle the panel between High intensity / Low intensity / Flashing.

To de-activate the LED panel, press the On-Off button for three seconds and it will turn OFF.

f) Use a USB cable to plug your smartphone into the 1A-OUT connection and confirm that it is charging via the little lightning symbol on your phone... You may want to wait for a few minutes to be sure...

g) Use a USB cable to plug your smartphone in the 2A-OUT connection and confirm that it is charging via the little lightning symbol on your phone... Again, you may want to wait for a few minutes to be sure...

Steps f) and g) are to ensure both the 1A and 2A connections function properly.

In the next step we will assemble the solar panel and test it.

Step 12: Prepare / Plug / Test the Solar Panel

a) Cut 5 feet of 16 AWG double-wire speaker cable. (Note: if your solar panel came with a wire already attached to it I would recommend that you replace it with a 16 AWG double-wire cable to eliminate the possibility of induced resistance.)

b) Separate the male portion of the DC connector.

c) Separate the two wires at one end of the 16 AWG cable for about an inch.

d) Align the end of the 16 AWG cable with the DC connector and cut a small piece off the negative wire (the positive wire connects to the middle of the connector while the negative wire connects to the outside part... see photos).

e) Using a + screwdriver, stretch both sides of the plastic component of the DC connector... this will help when you thread the double-wire cable through it.

f) Thread the double-wire cable through the plastic component of the DC connector. You start with the small end first. Move the plastic component a few inches backward from the end of the cable (see photos).

g) Strip 1/8 in. from both wire ends and add solder to them.

h) Add solder to the DC connector at the two locations where the two wires will be soldered (see photos).

i) Solder the two wires on the metal component of the DC connector ("+" for middle of connector and "-" for the exterior. Squeeze the metal part of the connector on the "-" wire to hold everything in place).

j) Move the plastic component forward on the wire and screw it on the metal component of the DC connector. You are done with this end of the cable.

k) Prepare the solar panel by adding solder on the "+" and "-" connections. You should end up with two shiny bubbles of solder.

l) Solder a 4N2002 diode on the "+" connector of the solar panel. The side of the diode with the white strip should be installed the farthest away from the solar panel.

m) At the other end of the cable, cut the negative wire so it aligns with the shiny bubble for the '-' side of the solar panel and cut the positive wire so it aligns with the led coming out of the diode (see picture).

n) Strip 1/8 in. of both wires and add solder.

o) It is a good idea to test for 0 ohm between the DC connector and the other end of the cable for both wires (see photos).

p) Connect the cable to the solar panel and diode. Make sure that the "-" cable goes with the "-" sign on the solar panel.

q) Secure the cable on the solar panel by adding a strip of household scotch tape.

r) Plug the solar panel's DC connector (male) in the female jack of the micro USB / DC power connector adapter. Plug the adaptor in the “5V-IN” of the Power Bank. The four charge level LEDs will turn on alternatively from left to right to show you the current level of charge and that it is in fact charging the Power Bank.

Step 13: A Few Important Notes


1- You need a certain amount of direct sun on the solar panel to really charge the Power Bank.

2- When you decide to charge your phone via one of the USB connectors, assuming that the Power Bank is fully charged, the four charge status LEDs will initially be ON solid... then after a while three LEDS will be ON solid... then after a while two LEDs will be ON solid... then after a while the leftmost LED will be ON solid... then after a while you will see the leftmost LED blink slowly which is telling you that the Power Bank is becoming depleted. Wait a little longer (assuming that your phone is not fully charged or you are on the last of multiple charges without having recharged the Power Bank via the micro-USB or on a sunny day) and the leftmost LED will start blinking faster... A little more time and all will go blank, telling you that the Power Bank is depleted.

3- Always have a look at the little lightning symbol on your phone to confirm that it is in fact being charged from the Power Bank when plugged into one of the two USB connectors (1 and 2 Amps).

4- If you can live without your phone for a short while, power it off before connecting it to a USB connector of your Power Bank... it will charge much faster.

5- Always keep the Power Bank in the shade and away from heat sources. One of the main objectives of this project was to move the solar panel away from the Power Bank.

6- I keep my Power Bank on a desk by a window while making sure that it is never exposed to direct sun or heat coming from our house heating system. The solar panel is positioned by the window and pointing upward toward the sun at a small angle.

Step 14: Call for Help

I hope you enjoyed/will enjoy building this project. I tried to be as detailed as possible in my explanations and to add as many photos as I believed to be useful. Hopefully it did not make it intimidating as it is in fact a fairly simple project. All one needs to do is proceed slowly and methodically to produce a fairly professional looking and fully functional DIY project.

As I mentioned in the introduction, my goal is that high schools/colleges/universities around the world will consider this Power Bank as a useful green project to be built by students and actually used on a day-to-day basis. This is why I would like to call on electronics experts (students, engineers, pro DIYers) to provide feedback on possible concerns and improvements. Once I am confident that the recipe is good, I plan to have this Instructables translated into a number of languages (starting with French which is my mother tongue) to help with its propagation. If all goes well, we might be able to go to bed at night feeling that we have made our own little contribution to help save our precious planet.

Sincerely yours, Pierre