Joule Thief

erco

I love this simple idea , since I hate throwing away alkaline batteries that have some life left in 'em. Or, try to power your 3.3V devices from one good AA battery...

http://www.instructables.com/id/Make-a-Joule-Thief

K2

erco, I like this circuit so much that I once bought a whole bag of power inductors and made night lights for my mountain cabin. I charge a series string of NiMH AA cells with a very inexpensive solar panel by day, and power the night lights with them by night.

I make a transformer out of the inductor by winding a few turns of fine wire around it.

Tubular

Give me your tired, your poor, your huddled masses of depleted AA batteries...

with apologies to Emma Lazarus

Phil Pilgrim (PhiPi)

For those without the patience for another tedious Instructables video, here's the PDF:

http://cachefly.oreilly.com/make/wp_joule_thief.pdf

It has all you need to know, including a schematic! (What a concept! )

-Phil

K2

IIRC, the original circuit was a Design Idea in Electronic Design magazine.

K2

Carla,

Seems like I have to try everything. A book I read back in grade school talked a bit about annealing iron wire to make a magnetically soft material. So while I was experimenting with this circuit, I stuck a wad of small finishing nails in a clay pot with a tight-fitting lid and fired them in a kiln to about 1850 deg F. After a long slow cool-down, I wrapped a few nails together with tape and then wound a few different combinations of primary and secondary turns, experimenting with each. Turns out that I could never get the same efficiency that a small power inductor core provided. But it did work.

Junked TV sets and switching power supplies can be a source of ferrite cores, but they're a hodgepodge of permeabilities and operating frequencies. Fortunately it's such a simple circuit that it makes experimentation easy.

Heater.

Carla22 and K2,

Yep. Lot's of ways to make that inductor. I built this circuit years ago from the design on Dick Cappels web site http://www.cappels.org/dproj/ledpage/leddrv.htm
He also shows there haw to get this working using a rusty nail.

Dick also has a thousand other interesting circuits that Parallaxians will no doubt appreciate many of which use PICs or AVRs but could be adapted to Propellers. Well worth checking out.

K2

I'm amazed at what you pulled out of your hat, Heater! What a great site!

Mark_T

For a regulated constant 3v3 a little more sophistication is required!

Ron Czapala

Pretty neat!

Here is mine...

Ron Czapala

Found an even smaller toroid in an old CFL bulb.

I used a 2N4401 transistor this time - it is soldered directly below the LED.