Technology
How-To: Build a battery-free flashlight

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Mr. Rigsby shares his design for an LED flashlight using two 220 farad(!) capacitors in place of all-too-familiar disposable batteries –

In this project, you will make a flashlight that works without batteries. Even more amazing, you can recharge it in three minutes and it will run for more than 24 hours. Because the ultra capacitors can be recharged thousands of times, you may save the environment from ever receiving an old flashlight in the trash system.

Very cool. It’s worth mentioning that the lengthy operating time from one charge wouldn’t provide constant illumination. In the Instructable’s comments, the author notes that after 2-3 hours the LED’s brightness would drop to “night light” levels. Others point out that this could be remedied to some extent by using a driver circuit to keep voltage levels up. Still, imagine fully charging a portable device in about 3 minutes – I smell future!

10 thoughts on “How-To: Build a battery-free flashlight

  1. a few years ago there was a bit of a hubub about Coleman’s FlashCell screwdriver and I tried to buy one but their site wasn’t even fully functional. I haven’t seen it in stores and the website is now somewhat of a ghost site, the store part has just been deleted.

    perhaps we need to build some sort of ultra cap based replacement battery for existing tools like screw drivers that don’t always need all the umph that a NiMH can provide

    http://www.popularmechanics.com/blogs/technology_news/4223118.html
    and
    http://www.flashcelldriver.com/

  2. Digikey sells capacitors up to 5000F !!
    Stored energy = 1/2 C V^2 = 0.5 * 5000 *2.7v*2.7v = 18 kJ = 5 watt-hours
    That’s a little more than the energy in 2 AA rechargeable NiMH batteries.

    The two 220 farad capacitors in this design store 320 mW-hours; that’s a little less than a standard CR2032 lithium watch battery.

  3. Got a question, what about one of those shaker charge generators? The capasitors are great, stored power. But how do you power it? Solar cell?

  4. “you may save the environment from ever receiving an old flashlight in the trash system”

    Why would you throw the flashlight away?

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