Led falshlight with magnetic powering?

I would bet that the electronics and magnet are dummies and the LEDs run strictly on the batteries. How long will you be able to resist taking it apart to find out?

Don't know about the batteries. Mine is just a capacitor, coil and sliding magnet. Shake it for a few seconds so the magnet inducts a current in the coil which charges the capacitor up enough to keep the LED lit for 4 or 5 minutes. Nothing like as good as my Coast Lenser V but because you never have to worry about dead batteries it is great for the glove compartment or a survival bag.

You would have to shake it for days to charge up a Nimh battery.

-- Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at:

. Yes that's what we figured ................... maybe even up to 8 or 10 minutes maximum?

But with all the excitement of opening other presents the methodical approach of actually timing how long it would light before the energy stored in the cap. was used up kinda got lost!

But still trying to figure out why the thing contains two seemingly 'ordinary' alkaline cells? It certainly seems to use the induced energy.

BTW I do recall some sort of hand cranked (one hand thumb and fingers etc.) flashlight probably around 1938 and of German manufacture IIRC. It only lit as long as the mechanism inside was whirring as you continually squeezed it in you hand.

Interesting because today there have been such major improvements in magnets and capacitors that what would have been impractical back then can be incorporated into a few dollars flashlight! The improvements in magnetic materials (and glues etc.) made possible loudspeakers that do not require the multi turn energising coils (also used as smoothing chokes) as previously.

. Terry writes further .................... yes as Bruder mentions; 'recharging' ordinary alkaline cells etc.

I always took that to be a case of sort of reactivating or maybe even slightly reversing some part of the chemical action of the primary cell? So maybe these 'shake and bake' flashlights do a bit of both; charge up a capacitor and with a bit of the energy going to 'reactivate' or at least prolong the life of very ordinary alkaline cells?

Any idea of the 'efficiency' of an induced energy flashlight? For example if I use the energy contained in one bottle of beer (or glass of good red wine) both possibly useful comparisons for this time of year, maybe, maybe not, to shake the flashlight, how many calories or coulombs of light energy will I get out?

Academic question; the idea in this instance being more the convenience and immediate availability of a light source while avoiding the long term storage and or deterioration of either storage or primary cells. But I guess if I trailed one behind the sailboat bobbing along in the wake or hung it in the cab of the pickup so it jiggled nicely (some bumpy roads here too!) it would be usefully charged! Many thanks for the discussion.

I have seen some $2 units in dollar stores where the "magnets" are pieces of plain steel rod without magnetism, the coil's leads are soldered together onto one spot on the PCB, the only semiconductor is the LED, and the only energy storage device is the pair of CR2032 cells.

It has been noted that not all $2 dollar store shake flashlights are such frauds.

I have seen others (at hardware stores for more than $2) with a switch that selected generator power or battery power.

- Don Klipstein ( snipped-for-privacy@misty.com)

Wouldn't that make them go blind? ;-)

Yep. The one I've currently got isn't that fancy, but it's *VERY* clearly operating "as-advertised" - Two diodes, a cap, the LED, and the coil, plus a switch, and of course, the magnet. Unless they've managed to cleverly disguise a battery as a capacitor, it really does do what it claims, without "cheating", and reasonably well. LIke I said in the other message, it isn't an eight-D Maglite, but... It was never intended to be.

I was playing with making one, sort of. I used a stepping motor with some diodes feeding an "ultracap" that I took out of a VCR. The light didn't really sustain itself for long, but you could see the capacitor charging up. Turn the knob, and there'd be some light, and turn it enough and the capacitor would get charged up.

SOme problems were that I could only find one "ultracap", though I know I've saved some more out of things. And most of the stepping motors I had were not conducive to easily adding a knob, so I couldn't play with different motors easily. When the spring comes, I'll remember and keep an eye out for junked VCRs and other things that might have "ultracaps" in them, and parallel them for longer power.

I have one of the commercially made crank ones. And it worked out of the box two or is it three years ago. I can't remember if I tried it without cranking, but there was light and of a reasonable length of time, from the moment I first tried it. That isn't likely the case if it's a chargeable battery in there. It's never gone dark, though I admit I don't use it that much (it is handy to know it's there and I don't have to worry about whether the batteries will be working). A minute of cranking, and it's back to full brightness.

Michael