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http://zabaleen.blogspot.de/2012/12/robin-hood-and-joule-thief-raiding.html
The fact that the Joule thief allows one to run a 3V LED from a 1.5 or 1.2 Volt battery would itself be astounding, because it means you only need half the number of batteries to get the same light. That in itself is a tremendous savings (imagine only needing to carry half the number of batteries up to Mt. Everest in your backpack to get the same light!).But it gets better!
Some of you are thinking "wait, maybe it enables you to use a single 1.5 volt battery to light a 3V LED instead of the usual two, but doesn't it just make that battery last half as long?
Great question, but the answer is that the Joule Thief, which works by building up and collapsing a magnetic field around the torus (which acts as an electromagnetic inductor) actually is more efficient than using a battery directly because it PULSES the energy to the LED. You see the lightbulb shining brightly, but in fact it is turning on and off very rapidly as the magnetic field of the inductor builds up and discharges again and again. That means that though the light appears to be on all the time it is actually turning on and off and saving energy because it isn't on all the time.
But it gets even better: It turns out that the Joule Thief enables the battery to keep supplying electrons to the light long after the battery is normally considered DEAD. So the battery actually lasts much much longer than a normal battery. And for this reason, in Nepal I was able to pick up dead batteries that tourists had thrown along the trail when they no longer ran their cameras, and use them to run my flashlight!
I've observed "dead" batteries working down to about 0.5 Volts. Normally a 1.5 V battery is considered dead when it reaches 1.0 volts. But the Joule Thief can "steal" the remaining energy much below that.
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Im going to flash my stupidity here for a second and suggest that can this not be used on 7.2v LED systems for extended runtimes?
Hat-tip, as ever, to [url= http://boingboing.net/2012/12/04/fun-family-science-project-md.html ]Boing Boing[/url]
That's what most LED lights do on low mode anyway.
Nothing new to see here, DC-DC converters have been around for a long time.
As for Li-ion batteries, they can't be discharged below a minimum voltage or you'll damage them, so you can't use this technique with them.
Ah, I thought low modes were at reduced amperage rather than slower flashes.
DO smart lamps have voltage cut offs then when LiIon packs get to a critical level?
DO smart lamps have voltage cut offs then when LiIon packs get to a critical level?
I don't know what's inside the lights but most Battery packs have a small circuit board that does exactly that.
Every day's a learnering day.