Paracord Solar USB Battery Backpack

Introduction: Paracord Solar USB Battery Backpack

About: After being laid off in 2009, I got rid of my car to save money. The difficult transition from a car to a bicycle led me to start Solarcycle and design USB chargers that keep smart phones alive.

Please click below to visit our Kickstarter project page to pre-order a production model!

This instructable is for building and attaching a light-weight, water resistant solar panel and battery to a backpack with paracord to charge a USB device like a smart phone.

Solarpad Solar Panel Specs:
* Size: W 6.5 inches X L 10.9 inches X H 0.6 inches

* Cable Length: 10.0 inches

* Output - Female USB 2.0 Type A Connector

* Nominal Output - Current: 1000mA | Voltage: 5 Volts

* Max Open Circuit Voltage: 6 Volts

* Cell Type: Monocrystalline * Cell Efficiency: 18.8%

* Compatible with Power Core Battery Only

Power Core USB Battery Specs:

* Time to Fully Charge Power Core @ 5V 1A: 3 hours

* Capacity: 3350mAh/3.6V * Type: 18650 Lithium-Ion

* Diameter: 1.2 inches * Body Length: 4.2 inches

* Cable Length: 7.0 inches * Weight: 100g (3.53 oz)

* Input - Male USB 2.0 Type A Connector

* Input - Current: 450 to 1300mA | Voltage: 5 to 6 Volts

* Output - Female USB 2.0 Type A Connector

* Output - Current: 500mA | Voltage: 5 Volts

* Body Material: Aluminum Tube with Plastic Caps

* Battery Life Under Typical Use: 5 years

* Provides up to 140% iPhone Charge or 70% Galaxy S4 Charge

* Compatible with iPhone, Android, Windows Phone, and Others

Circuit Efficiency So Far:

By dividing the # iPhone charges by the ratio of Power Core rated capacity to iPhone rated capacity [1.4/(3350/1448)], the total system efficiency is roughly about 61%, which means about 61% of the energy coming from the stored energy in Power Core reaches your phone's battery. Keep in mind that the energy is going through many regulation circuits inside Power Core and inside your phone, so energy is lost at each regulation step before reaching the phone's battery. These tests were done with the phone on and the screen off, so maybe a better calculation is with the phone shut down. Further tests by verifying battery capacity and charge current with current meter data loggers and taking the integral of the data curves will make this calculation more accurate. Also, refinement of the circuit and better heat management can lead to improved efficiency ratings. However, even at 61% efficiency, Power Core still performs better than any battery of similar size on the market.

*WARNING: Be careful when handling any Lithium-Ion battery because shorting the battery can cause burns. Always wear safety goggles. Please use recommended battery and circuit components because of the higher 2000mA max battery charge current involved.FCC Compliance: NOT Required because the circuit frequencies are below 1.7MHz

Step 1: Materials and Tools

Here is a list of the materials, tools, and files required.


QTY Description

1 Solar Panel (Layout Drawings can be downloaded at Suntactics solar panels are recommended because they have the highest verified power output. You can try to cut your own solar cells using this instructable or you can contact to build one for you. You may have to supply some materials to Suntactics for a few prototypes because they are not off-the-shelf products yet.)

1 Power Core Battery (Instructions on how to build this USB Lithium Ion rechargeable battery can be found here:

1 9 foot piece of paracord

1 Backpack

1 1" Wide Kapton Tape Roll

1 Roll of solder wire

2 Epoxy Mixing Nozzles (Epoxy may harden in nozzle so have spares just in case

2 3' USB Male-Female USB 2.0 Type A Extension Cable (Cable drawing can be downloaded at Ever Red cables have good water resistance. Some are sold on Ebay)


1 Wire stripper

1 Scissors

1 Multimeter

1 Soldering Iron

1 Drill

1 3/16" Drill bit

1 3M Manual Epoxy Applicator Gun EPX (I think they are changing the gun to a metal design but I found a plastic version here

Step 2: Build the Solar Panel

If the solar panel doesn't come with holes along the edge, you can make the holes by drilling holes with a drill using the 3/16" drill bit. These will be the holes for paracord. Drill as many holes as needed for tying the solar panel to your backpack.

Cut one of the USB cables 21" from the male end. Strip the outer jacket .5" from the end, remove the shielding, and strip the Black and Red wires about .25" from the end. Cut away the Green and White wires because they aren't needed. The back of the panel should have two leads. To verify the polarity, just attach a Volt meter to the leads and shine a light on the panel. Positive voltage means that the positive and negative leads are in the correct orientation. (I've had a panel with reversed orientation, so it is always good to check before soldering) Bend the leads to the side and place Kapton tape on top of the exposed leads that are not being soldered to. This protects exposed leads from moisture. You can also apply epoxy to them, but it would take more time. (Having the USB cable come out from the side creates a service loop within the plastic body giving it a retractable cord effect) Solder the USB Red wire to the positive lead and the Black wire to the negative lead. Push the leads down to be flat as possible. Build a Kapton tape wall around the soldered leads and cable with about a .25" gap around the leads. This wall will contain the epoxy, which acts as a water sealant and cable strain relief. Make sure some of the cable jacket is within the Kapton wall to make a good strain relief.

Attach the mixing nozzle to the applicator gun. Ideally you want to use an applicator gun for this step to get in to the tight spaces. It may be possible to do it without an applicator gun, but it might take a longer time and be more messy. Either way, be sure to have a few sheets of plastic to do work over and to rest the epoxy applicator down on to catch any epoxy spills. This epoxy has a working time of only 5 minutes and hardens quickly, which is why all the parts are prepared for epoxy first. Try to keep the epoxy flowing in the nozzle or it will harden inside prematurely and you have to replace the nozzle. As it hardens, the epoxy does get hot, which is a normal exothermic reaction. If epoxy spills on something, be sure to clean it up right away before it hardens. Also, epoxy can give off a strong odor so be sure to work in a ventilated area.

Fill the Kapton walls with epoxy so that it barely covers the wires.

Remove the mixing nozzle from the applicator and put the cap on the tube or it could seal the epoxy inside the tube.

After 10 minutes the epoxy should harden, but may still be tacky and rubbery so don't touch the epoxy. At this stage, you can trim excess epoxy away with a knife.

Step 3: Attach the Solar Panel to the Backpack

With the 9 foot piece of paracord, weave the cord through the holes drilled in the solar panel edge. I just used 4 holes located in the corners of the panel. Once the paracord is weaved through, tie the panel to a loop of the backpack. I tied the panel to the handle at the top of my backpack.

Finally, attach the Power Core battery to the solar panel and tuck the battery in a pocket in the backpack. I used the vertical zip up pouch in the back to store the battery.

Now the backpack is ready to store solar energy in a battery while hiking or just walking around!

CONGRATULATIONS!! You made a paracord solar USB battery backpack!

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    7 years ago on Introduction

    This is amaing! I'm so inspired and inquisitive and i want to make this now! Imagine getting my phone charged while I come to and from school! haha :P could these 2 be combined? o.O