One thing which has always bugged me is knowing that all the batteries I discarded over the years still had juice in them... between my Walkman and my digital camera, I'm sure I've thrown away or recycled enough power to light up a small village. File under "If I'd only had one of these years ago": The wonderfully ingenious guys over at MAKE: Blog and Evil Mad Scientist have come up with this handy little DIY project which lets you eke every last little milliamp from those supposedly "dead" batteries waiting to be recycled.

So whatsa Joule Thief? It's a little wisp of a circuit that allows you to drive a blue or white LED from a low voltage. Normally, if you want to light up a blue or white LED you need to provide it with 3 - 3.5 V, like from a 3 V lithium coin cell. But a 1.5 V battery like a AA cell simply will not work. But using the Joule Thief, it works like a charm. Not only does it work with a brand new battery, but it works until the battery is nearly dead-- down to 0.3 V. That's well below the point where your other toys will tell you the battery is dead, so it can steal every last joule of energy from the battery (hence the name).

Of course, it's far more green to use rechargeable batteries, period. But the next time you change the batteries out of your remote, I bet you find some old-fashioned alkaline AAAs with enough juice to fire up one of these little gadgets. A quick trip to Radioshack, and you've got yourself a post-apocalyptic booklight to use while you RTFM! Just remember to use lead-free solder.

via Evil Mad Scientist

Comments (4)

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Here is an easier way to squeeze more li
written by Ashleigh , November 08, 2007

Too much trouble to do what your saying. There's simple, better way to extend the life of 1.5V AA,AAA,C&D batteries. I just put them in a Battery Xtender and recharge them. I can also use the Battery Xtender to recharge rechargeable batteries at the same time!
This is an amazing product that has saved me lots of money and at the same time I'm helping the environment.
Lots of great reviews on the web site from users. www.batteryxtender.com

...
written by Soda Pop , November 09, 2007

What we need is a device to suck the remaining juice out to recharge another cell.

Now, if you have use for little leds around your house this may be the project for you. Cordless night-lights or something.

To Ashleigh
written by Glen , January 04, 2008

You miss the point of this.

The circuit is designed to get more use out of bateries you would normally throw away.

Your "battery extender" is just using up mains electricity to top up your batteries. Very wasteful.

I think it's a great idea....
written by leiram , November 23, 2008

...but how exactly does this become practical? I mean, you need to hold it. How would I use it, for example, to power the nightlight in my bathroom? I hope I'm not being too negative

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