Building a portable solar phone charger is a simple task that can be completed within five minutes. This compact device draws power entirely from solar energy and is small enough to slip into your pocket. It is equipped with a built-in stand for ease of use and has been confirmed to work with Apple devices, including the iPod Touch and a Quadcore Android phone.
Before venturing into creating educational science projects online, my experience was rooted in teaching middle school science. These days, my work revolves around developing hands-on activities for students and enthusiasts through my website, BrownDogGadgets.
Portable solar phone charger (Photo: Phone Charging Station/Getty Images)
While going through different blogs this Earth Day morning, it became obvious that many were highlighting solar-powered USB chargers. While the designs were interesting, their price tags were discouraging, with most costing upwards of $60 and still failing to match my personal preferences.
Several useful guides are available on Instructables for making Solar USB Chargers. One popular option involves using a Lady Ada Minty Boost circuit paired with a solar panel and lithium-ion battery, but it tends to be costly and too complex for a casual weekend project.
Fortunately, there is a method to build a better, more affordable charger for less than $20, small enough to fit discreetly inside an Altoids Tin. It maintains a stylish and practical appearance.
*** Update: This original kit has been retired due to durability concerns. Improved versions, such as the Solar USB Kit 2.0 and the more durable Lithium Heavy Duty 2.0, have been introduced.
For those interested in something pre-assembled, especially for outdoor activities or emergencies, Folding USB Solar Cells are available at affordable prices and offer much higher efficiency.
Step 1: Materials You Will Require
Parts Needed:
- USB Charging Circuit
- Solar Panel rated at 4V or more
- AA Battery Holder
- Rechargeable AA Batteries
- 1N914 Diode
- Altoids Tin or any similar container
- Electrical Wire
Tools Needed:
- Soldering Iron
- Solder
- Tin Snips
- Hot Glue Gun with Glue Sticks
- Electrical Tape
The estimated cost remains under $30, and buying in bulk could reduce the cost to under $10. A complete kit is available through BrownDogGadgets.com, and for those preferring ready-made options, several assembled chargers housed in various tins are on offer.
Step 2: Setting Up the DC to USB Converter
The key component for this project is the DC to USB converter, which transforms AA battery power into the 5V output necessary for USB devices. There are different approaches to this.
One option is to assemble a Minty Boost kit from Lady Ada, which costs $20 and involves soldering. It can charge nearly any gadget, including newer Apple products.
Another way is to purchase a ready-made converter, either from online stores like eBay or from BrownDogGadgets.com, usually priced around $10, and compatible with devices like Kindles, iPhones, GPS units, and Android phones.
An alternative method is salvaging the circuit from a cheap USB charger found on eBay or Amazon. Be aware, though, that some may not work properly with Apple products, so it may be wise to buy a few spares.
It is advisable to avoid building a 6V or 9V circuit and using a voltage limiter to adjust it to 5V, as this approach wastes energy.
Step 3: Selecting Appropriate Batteries
A common flaw with commercial solar chargers is their low-capacity internal batteries, often capped at just 1000 mAh. A single AA rechargeable battery holds between 2000 – 3000 mAh, offering far better performance.
Rechargeable batteries are essential for this build. NiMh AA batteries are recommended for their affordability, reliability, and easy availability. Many people already have them at home. Using two AAs provides between 2000 – 3000 mAh of current, and pairing two sets in parallel can boost it to 4000 – 6000 mAh.
Another advantage is that the batteries can be removed for charging or replacement, offering more flexibility.
For projects requiring a smaller build, compact NiMh battery packs available from stores like American Science and Surplus or various online sources are a practical choice.
Step 4: Choosing the Right Solar Panel
Considering that two rechargeable AAs produce about 2.4V combined, the project requires a solar panel capable of delivering at least 3V to 4V for effective charging.
Space constraints, due to fitting everything inside an Altoids Tin, mean a compact solar panel is preferable. Some 4V solar panels are a perfect fit and perform excellently, similar to those used in the Solar AA Altoids Charger project.
While larger solar panels would offer more charging power, they simply would not fit within the desired casing.
It is possible to combine smaller cells, such as two 2V panels, to achieve the necessary voltage. They can be easily sourced from online marketplaces.
When charging NiMh batteries, it is important not to exceed 10% of their capacity in charging current. For example, a 2000 mAh battery should not be charged with more than 200 mA. This usually becomes an issue only if using very large solar panels.
Step 5: Wiring the Solar Panel
The first wiring task involves the solar panel.
The 1N914 diode should be soldered directly to the positive tab of the panel, ensuring the diode’s black band faces away from the panel. This prevents power from leaking back into the panel.
Attach a wire to the other end of the diode (the red wire shown in the photo), and another wire to the negative solder point (the black wire shown). Finally, cover the connections with tape to protect them.
Step 6: Attaching the Battery Pack
Battery Charging Station (Photo: Twitter)
At this stage, the solar panel wires are joined with the battery pack wires.
Match all positive wires together (typically red) and all negative wires together (typically black), and solder them.
This step is straightforward and ensures that the solar panel can properly charge the batteries.
Step 7: Preparing the USB Charger
The USB charger circuit used here usually has some LEDs installed, which are unnecessary and waste energy. Removing them is recommended to preserve battery life.
Caution is necessary when removing components, especially if unfamiliar with the circuitry. Those attempting this should avoid reckless cutting to prevent injuries.
If using a cheap USB charger, the circuit must be removed from its plastic casing, and all unnecessary wires and battery connections should be detached.
It is important to identify where the positive and negative power connections are located, usually marked on the board, and to be mindful of any integrated switches.
Step 8: Soldering the Charger Circuit
The next step involves connecting the positive wires (red in this case) to the positive terminal on the charger board and the negative wires (black) to the negative terminal.
Once this is completed, the entire circuit can be tested.
Charging devices should be possible using only sunlight, and the batteries will also charge devices when sunlight is unavailable.
Step 9: Modifying the Tin
Altoids Tins are preferred for this project due to their convenient size and appearance.
A hole must be cut into the tin to allow access to the USB port, which can be done with tin snips.
For a more polished finish, a Dremel tool can be used to create a neatly shaped opening, although a simple snip is usually sufficient.
Step 10: Securing the Components Inside
For added safety, laying down a strip of electrical tape under the bare circuit board is advisable to prevent short circuits.
After that, the final step is assembling everything securely inside the tin using hot glue, ensuring that all parts stay firmly in place during use.
