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View Full Version : Joule Thief - DIY LED light



blackdog
2005-02-11, 16:05
Found this interesting circuit for making LED lights.
http://www.emanator.demon.co.uk/bigclive/joule.htm

Seems perfect for the ultralight diy hikertronics geek out there.

Feel free to ignore.

Lanthar
2005-02-11, 17:34
nice, i wonder how much long / bright it will last on a button cell or aaa?

blackdog
2005-02-11, 18:35
The amazing thing about this circuit is that it will run right down to about 0.35V if left running continuously, and will often provide a week of continuous low level light from a battery that would normally be considered dead.

If AAA means half the capacity of AA then... Half a week? I can only speculate. Where are all soldergeeks when you need one?

Mutinousdoug
2005-02-11, 19:35
I just bought some NiMH batteries in AA and AAA and the ratings for them are AA=2500mAh vs the AAA=850mAh at 1.25VDC. I think Alcalines are 1800mAh and 750mAh at 1.50 VDC respectively. So about 2.4/1.0 AAs over AAAs for Alcaline.
This is probably not a good application for rechargable batteries since they aren't supposed to like complete discharge.
Like Blackdog says: interesting but geeky. Or: geeky but interesting.

blackdog
2005-02-12, 07:39
This is probably not a good application for rechargable batteries since they aren't supposed to like complete discharge.
A LED light is usually turned off before it dies by itself... The circuit is powered by a single battery and may use even "half-dead" ones, left-overs. It is powerful enough to power up to 6 LEDs. It certainly invites to some experimenting.

So if there's a supplier of the transistor within reasonable distance, I'll build a Joule Thief (or three) for myself. If not then there's an alternative circuit:
http://www.uoguelph.ca/~antoon/circ/ledflash.htm

The experiments have to wait, though. A Joule would have been a good thing to bring on the journey, but the lack of time means I have to buy a LED light instead. A green one, probably. The bazaar would have been a good thing now.