You’re on a camping trip and you need your daily dose of ENGINEERING.com, so every morning you read it using your smartphone. The articles are so interesting that you keep reading, lose track of time, and drain your phone’s battery. There’s not an outlet for miles. What to do? If the EnergyBionics Kickstarter campaign is successful, you might just reach for the solar powered battery charger on your wrist!
The Carbon wearable charger contains a 650 mAh lithium polymer battery that can provide several hours of charge to your smartphone, camera, or other personal electronic device. Its output can deliver up to 5 Watts at 1 Amp - enough to recharge a phone in about 30 minutes.
Unlike many other “spare battery” gadgets, the Carbon recharges its own battery using a monocrystalline photovoltaic cell. EnergyBionics claims that in full sunlight, the on-board battery can be recharged in two to three hours. (I calculate closer to ten hours*.) The PV cell also responds well to artificial light so the Carbon can recharge indoors too. In order to maximize the solar energy conversion, the circuitry includes a low-power microcontroller that runs a maximum power point tracking (MPPT) algorithm. And if you’re not too far from civilization, the Carbon can also be charged in about 30 minutes through a USB interface.
The Carbon has been under design for several years, and after thorough proof of concept and prototype testing, EnergyBionics is ready to move into the final design and production stages. The company hopes to raise $48,000 over the next month in order to refine the design, conduct FCC, ETL, and CE certification tests, and secure manufacturing partners.
For the next generation of Carbon, they might want to add a small pendulum and generator to convert kinetic movement into electricity, like self-powered quartz watches do. This would supplement the solar power and allow you to wear the charger under long sleeves or in low light and still generate electricity. They don’t indicate whether the battery is replaceable, but a lithium polymer battery typically gives about 500 deep discharge cycles - over a thousand if you only discharge it halfway - so the battery could need replacement after one to five years, depending on how often it’s used. As supercapacitors improve their energy densities, I can see them eventually replacing the battery in this type of application, allowing near limitless charge-discharge cycles.
As we rely more and more on our handheld electronic devices, we’ll need ways to recharge them when outlets aren’t nearby. Energy harvesting devices like the Carbon offer a functional piece of “high-tech jewelry” to keep our gadgets running.
Images and video courtesy of EnergyBionics
The PV cell is about 15cm2.
Full sunlight delivers about 1000w/m2, so there's roughly 1.5W of solar power shining on the cell.
At 22% efficient, which is what the manufacturer lists for the cell, 0.33W is converted to electricity.
The battery has 650mAh of capacity. At 5V, that's 3.25Wh of energy.
With 0.33W, it takes about 10 hours of full sun to fully charge the battery to 3.25Wh.
I guess that's even more reason to add a kinetic energy converter to the design!