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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

Step 1: Materials, Tools, and Files Required

Here is a list of the materials, tools, and files required. Links to purchase or download most items are provided. The items in the Solarcycle Shapeways shop can be downloaded for free or purchased directly and are marked up as follows: $1 mark-up for small components, $2 for medium components, and $5 for large components. Mark-up funds will go toward maintaining the Solarcycle site and improving solar charger technology. Shapeways tends to have very good quality 3-D printing in all sorts of colors and materials. Results may vary with other 3-D printing methods. 3-D files, Gerber files, schematics, and part drawings can be downloaded from www.solarcyclepower.com


QTY Description

1 Solarpad Bracket http://www.shapeways.com/shops/Solarcycle

2 Solarpad Edge Trim http://www.shapeways.com/shops/Solarcycle

1 Solar Panel (Layout Drawings can be downloaded at http://www.solarcyclepower.com/index/Open_Source.h... 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 http://www.instructables.com/id/Ultra-Portable-Dre... or you can contact www.suntactics.com 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 Stainless Steel 1/4-20 Nut (The thinner nut height the better http://www.mcmaster.com/#stainless-steel-hex-nuts/...)

2 1.5' long polypropylene 1 inch wide strap (Make sure they when you cut the straps, you melt the ends to prevent fraying. Use 2 extra straps for extensions to wrap around larger cargo like backpacks or tent bags. You can also make longer straps http://www.acehardware.com/product/index.jsp?produ...)

2 1" Plastic side release strap buckle set (Use 2 extra buckles for extensions to wrap around larger cargo like backpacks or tent bags. Available at Ace Hardware. Reference http://www.bulkstrap.com/plastic-hardware.php)

1 Power Core End Cap http://www.shapeways.com/shops/Solarcycle

1 Power Core Cap Shroud http://www.shapeways.com/shops/Solarcycle

1 Power Core LED Cap http://www.shapeways.com/shops/Solarcycle

1 Power Core Circuit (Schematic, Gerber Files, etc. can be downloaded at http://www.solarcyclepower.com/index/Open_Source.h... Some can be purchased on Ebay http://www.ebay.com/itm/271412305343?ssPageName=ST... The main IC components are the Maxim MAX8903G charge controller and MAX1790 DC-DC step-up converter circuits)

1 NCR18650B 3350mAh Unprotected Panasonic Lithium Ion Battery www.ebay.com (If lower cost is necessary, try the Panasonic NCR18650A battery with a slightly less capacity of 3070mAh. Make sure it's unprotected and check the battery part number carefully. Protected batteries have added length with a built-in circuit, which may affect performance. Reference http://industrial.panasonic.com/www-cgi/jvcr13pz.c... Other brands of batteries are NOT recommended because the charge controller current to the battery can be as high as 2000mA and the Panasonic NCR18650 chemistry can handle it. If you need to use other brands, make sure that they meet the same specifications, chemistry, and can handle up to 2Amps of charge current. Using batteries that don't meet these specifications can lead to dangerous battery damage.)

1 Green 5mm Straw Hat LED www.ebay.com

2 Hirose 2-pin connector DF3-2S-2C http://www.digikey.com/product-detail/en/DF3-2S-2C...

2 Hirose 4-pin connector DF3-4S-2C http://www.digikey.com/product-detail/en/DF3-4S-2C...

10 Hirose Socket 24-28 AWG Crimp Pin DF3-2428SCC http://www.digikey.com/product-detail/en/DF3-2428S...

2 2.3mm X 60mm (.09" X 2.5") Cable Tie http://www.centralcomputers.com/catalog/product.js...

2 3' USB Male-Female USB 2.0 Type A Extension Cable (Cable drawing can be downloaded at http://www.solarcyclepower.com/index/Open_Source.h... Ever Red cables have good water resistance. Some are sold on Ebay http://www.ebay.com/itm/271412290808?ssPageName=ST...)

1 12" Rip Tie Lite http://www.frys.com/product/937708?site=sr:SEARCH:...

1 Aluminum tube 4.19" Long (Cutting the tube to size with a hacksaw and filing the end seems to work best. Pipe cutters tend to crush the tube. Anodize optional, fine sandpaper hand polish works good too http://www.mcmaster.com/#89965k631/=qu57q8)

1 1" Wide Kapton Tape Roll http://www.mcmaster.com/#7648a715/=qu5807

2 1" Kapton Tape Disc http://www.mcmaster.com/#77595a35/=qu586k

1 1" Dia Piece of Heat Shrink Tubing 2.7" Long http://www.frys.com/product/3222501?site=sr:SEARCH...

2 1/16" Piece of Heat Shrink Tubing 1.0" Long http://www.frys.com/product/3221391?site=sr:SEARCH...

1 1.7oz (50mL) 3M Sotch-Weld Dp-100 Plus Clear Epoxy http://www.grainger.com/search?searchQuery=dp-100+...

1 Roll of solder wire

6 Aluminum 1/8" POP Rivets .126"-.187" Mat'l Thk http://www.mcmaster.com/#97447a020/=qu7adi

2 Epoxy Mixing Nozzles (Epoxy may harden in nozzle so have spares just in case http://www.mcmaster.com/#catalog/120/3413/=qu7buz)

Various Lengths 26 AWG Standard Red and Black Stranded 4 Amp Max Wire Listed Below: http://www.mcmaster.com/#catalog/119/798/=qu7rf6

1 .96" Red Wire .06 strip one end .20 strip the other end

1 8.00" Red Wire .06 strip one end .20 strip the other end

1 1.06" Black Wire .06 strip one end .20 strip the other end

1 6.10" Black Wire .06 strip one end .20 strip the other end


QTY Description

1 Power Core Battery Fixture https://www.shapeways.com/shops/Solarcycle

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 http://www.uline.com/Product/Detail/H-3803/Adhesiv...)

1 Wire Strippers 24-26 gage range

1 Wire Crimper 20-24 gage range

2 Quick Grip Clamps able to open at least 6 inches

1 POP Rivet Gun (I used PowerLink 30 and it seems hard to find online, but I'm sure any POP rivet gun will work)

1 Tape Measure (Precision Calipers recommended for scribing cuts)

1 Third Hand Soldering Clamp

1 Soldering Iron

1 Heat Gun

1 Multimeter

1 Piece of Rubber .6" Dia. X .3" H

1 Scissors

<p>Thank you for your Instructable</p><p>Nice job.</p><p>Rima</p>
<p>Learn how to make your own solar panels and save tons of money http://cheap-solarenergy.blogspot.com</p>
<p>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</p>
<p>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?</p>
<p>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!</p>
<p>Thank you for putting that to bed for me. I suspected as much, but its nice to hear someone confirm it. </p>
<p>Yes, that is why I made Solarpad and Open Source project for people to see what's inside and what works.</p>
<p>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.</p>
<p>This is great. With all the things going on around us about solar energy we forget that fundamentally <a href="http://www.sunipod.com" rel="nofollow">solar energy</a> <br> is the natural evolution of the electricity, power and energy industry. <br> If the consumer also becomes the generator and all are electricity self <br> sufficient where <a href="http://www.sunipod.com/solar-power-station-lowers-electric-bill.php" rel="nofollow">solar solutions</a> seem to be going then imagine what fantastic future we can build for ourselves.</p>
<p>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.</p>
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.
<p>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.</p><p>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.</p>

About This Instructable


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Bio: 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 ... More »
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