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"Finally, A Proper Solar Charger For Hikers And Bikers" - Cult of Mac

Can a compact solar USB charger charge a phone and an external battery at the same time in about 3 hours? Yes! This is an Open Source Hardware instruction manual on how to build the Solarpad Kit solar USB charger, which includes the Solarpad solar panel and Power Core USB battery.

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Why Open Source Hardware?

The solar USB charging market has become saturated with low-quality and poor performing products and every year the big companies are selling the same products with very little improvement. Therefore, Solarcycle has developed its open source solar USB charger to empower customers with the ability to build their own solar USB chargers and to prove that a better solar charger that outperforms anything else on the market is possible.3-D files, Gerber files, schematics, and part drawings can be downloaded from www.solarcyclepower.com

This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

What's Special About Solarpad?

Our Solarpad Kit sets a new standard for a rugged, lightweight, compact, powerful, water resistant, and easy-to-use USB solar charger that can keep a smart phone charged all day! Connect Solarpad to the Power Core battery input then use the cable that came with your smart phone and plug it in to the Power Core output. Solar charge the Power Core battery and charge your phone from this battery at the same time! We designed the Solarpad Kit without an on/off button so you just plug it in and it works automatically! If a phone has a unique connector, one end of its charge cable always has a standard USB compatible plug. No extra cables are required because they are built-in. Use the Solarpad Kit on your next adventure! Will not leave you powerless.

The Solarpad Kit is designed to outlive the life of your Smart Phone! Solarpad uses a high-quality, custom Suntactics solar panel, which has a fluoropolymer film with the best light transmission, precision cut and tabbed high-efficiency solar cells, and a high-strength substrate. The panel is attached to a housing, which holds the buckle straps and 1/4-20 tripod thread in place. Our Power Core battery uses a high-efficiency, high-power charge controller from Maxim and the housing is sealed with high-strength epoxy, which prevents water from leaking in. Also, Power Core uses the same battery that's used in the Tesla electric car, which is the best battery of its kind. Even the built-in USB cables consist of thicker gage wire, which allows the electricity to flow more efficiently. The Solarpad Kit is engineered to squeeze the most energy possible from the sun's rays in to your smart phone. No short-cuts that compromise power or efficiency are taken, period.

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

* Strap Material: Polypropylene * Strap Length: 1.5 Feet

* Fastener Style: Plastic Side Release Buckle

* Cable Length: 10.0 inches * Weight: 270g (9.52 oz)

* Body Material: Plastic

* 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.

This Instructable is broken down into 9 sections:

  1. Materials, Tools, and Files Required
  2. Solarpad Assembly
  3. Power Core Battery Assembly
  4. Power Core Cable Assembly
  5. Epoxy Stage
  6. Power Core Final Test (How the Circuit Works)
  7. Power Core Final Assembly
  8. Solarpad Kit Final Assembly
  9. Safety and Troubleshooting

*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

Estimated Completion Time: 2 to 3 hours

SparkySolar10 months ago

Thank you for your Instructable

Nice job.


Malkaris1 year ago

Does it make more sense to connect the solarpad to the power-controller by something other than USB? It's sort of expected USB will be 5v

Question. I also built a solar charger from a Car USB charger. Could not get the chargers LED to light up on a 6v 1 watt Solar panel. Tested the output on the panel to 6.3 Volts.. I was able to use a 9v battery to get it to work. I was also able to use 2 6v 1 watt panels to get it to work. Almost every build I see uses 1 panel between 4 and 6v. Am I missing something?

Solarcycle (author)  mhutchinson41 year ago

Those car chargers are built for 12V car batteries. Some car chargers may only work closer to 12 Volts, but some may work at lower voltages, but not guaranteed. Maybe the other people got lucky and bought a car charger that works at lower voltage. Be aware that dropping the voltage from 12V to 6V is VERY inefficient and will cut your power output by half!

Thank you for putting that to bed for me. I suspected as much, but its nice to hear someone confirm it.

Solarcycle (author)  mhutchinson41 year ago

Yes, that is why I made Solarpad and Open Source project for people to see what's inside and what works.

I have ordered a few USB boost circuits. LOL, there are less than half the price I paid for the charger ($5).... Go figure. You live and you learn.

This is great. With all the things going on around us about solar energy we forget that fundamentally solar energy
is the natural evolution of the electricity, power and energy industry.
If the consumer also becomes the generator and all are electricity self
sufficient where solar solutions seem to be going then imagine what fantastic future we can build for ourselves.

Solarcycle (author)  AbhishekGupta1 year ago

I agree, this goes beyond green technology. It's just technology that works, like any other tool we use. But like any technology, high quality means it will last longer and work more effectively.

One an buy a 18560 battery with solder tabs. Soldering directly to a batteries terminals heats the battery internally which is not a good thing.
Solarcycle (author)  peabody19291 year ago

First, I recommend using the Panasonic NCR18650B batteries because they are the best on the market with verified and tested 3350mAh capacity. These batteries are hard to find with solder tabs.

Second, the solder tabs that are attached are spot welded on anyways so the battery gets hot during any manufacturing process and it's hard to control the dimension of the tab, which may make it too big to fit in the tube.