Dead batteries are the scourge of cellphone jockeys and iPod people everywhere. But you can avoid volt loss by charging your gadgets while you carry them. Just equip an old messenger bag with a lightweight, weather-proof solar panel, a simple connector and a few electronic bits, and the sun will do the rest. With a panel this small, don’t expect to fully restore a dead iPod in an afternoon, but an hour of light can top off a semi-charged battery or create enough juice to make a call. (You don’t even have to be outside—just set the bag near a sunny window.) No more suffering in silence.
Parts List
- A Messenger Bag (salvaged)
- Iowa Thin Film Technologies PowerFilm® WeatherPro™ Series P7.2-75 (Jameco #228161; $39.89)
- USB 6’ Cable w/Female Connector (Jameco #222068; $1.65)
- 78M05 Voltage Regulator (Jameco #192233; 19¢)
- 0.47 µF 50 V Electrolytic Capacitor (Jameco #330464; 4¢)
- 0.1 µF 50 V Tantalum Capacitor (Jameco #545570; 31¢)
- Salvaged Plastic Project Box
- Clear Vinyl Sheet (craft store; 50¢)
- Large Eyelet Kit (craft store; $2.45)
- Clips
- Wire
NOTE: There are four distinct subassemblies which constitute our eBag: (1) modified messenger bag, (2) photovoltaic panel, (3) voltage regulator, and (4) USB connector.
Assembly Instructions
- Depending upon the style of your messenger bag, you may or may not have to perform any or all of these modifications. Generally, the outside flap of the messenger bag should be equipped with a clear pocket for holding the photovoltaic panel. You can make your own clear pocket from vinyl sheet. Likewise, you will need several grommets or eyelets for routing your cables through the messenger bag. Add as many eyelets as necessary for connecting your charging “dock” with the voltage regulator and the photovoltaic panel.
- Preparing the photovoltaic panel has been simplified by the manufacturer-attached solder tabs. These tabs are pre-wired as positive (+) and negative (-) terminals. Either solder directly to these tabs or use removable clips for greater flexibility in moving the panel in and out of the bag.
- Mount the 78M05 voltage regulator inside your salvaged plastic project box.
- The two capacitors must be soldered to the 78M05 voltage regulator. The positive lead of the 0.47µF electrolytic capacitor is soldered directly to the input lead of the 78M05 voltage regulator. Conversely, the positive lead of the 0.1µF Tantalum capacitor is soldered to the voltage regulator’s output lead. Finally, the negative leads of both capacitors are soldered to the ground (GND) lead of the 78M05 voltage regulator.
- Snip off and discard the male connector from the USB cable. Open this newly exposed cable end and separate the four wires: red, black, green, and white. The green and white wires are USB data lines and they are not used. The red wire is connected to the output lead of the 78M05 voltage regulator. The black wire is connected voltage regulator’s ground lead.
- Connect the photovoltaic panel’s positive terminal to the input lead of the 78M05 voltage regulator and the panel’s negative terminal to the voltage regulator’s ground lead.
- Place the photovoltaic panel in direct sunlight and test the voltage readings with a digital multimeter at these four points: photovoltaic panel terminals, voltage regulator input, voltage regulator output, and USB pin 1 + 4. The readings at the first two points should both be approximately 7 – 8 volts. The readings at the last two points should be exactly 5.15 Volts. If you obtain valid voltage readings, try connecting one of your USB-chargeable devices to the eBag’s output USB female connector.
- During testing we found that iPod nano (first generation) and Sony PSP charged reliably with this setup. Unfortunately, we were not able to charge a Motorola RAZR V3 phone or an iPod shuffle (first generation).
If everything checks out, assemble the photovoltaic panel, voltage regulator, and wiring inside your messenger bag, hook up a suitable device and charge out there.
