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Are there any real magnetic induction shake-to-charge flashlights out there? Phil Karras relates his run-in with some more flagrant fakes on his website:
"I'm not saying that the flashlights were not worth the $2.50 I paid, but they were not as advertised. The flashlight box clearly stated in poor, but understandable English, that the flashlight did NOT use batteries, all you had to do to make it light was to shake it back and forth.
On my way out I heard someone say that there was no magnet inside the flashlight. Instead of going right back to the vendor, though, I went home and ran an experiment. I left one of the flashlights on while I went out for a couple hours. When I returned, the flashlight was dark. I picked it up and shook it, but no amount of shaking would make it shine again."
"A closer look inside showed what looked like two button-cell batteries. I took the unit apart and inside there were two 2032 button cells, an on-off switch that was attached to the batteries, and two wires from the coil going to a circuit board with nothing on it--no diodes, no chips, nothing but unused solder pads.I then took the "magnet" out and found that it was not a magnet--just a lump of non-magnetic metal. A closer look at the coil showed that it was one layer of wire only, hardly enough to generate any useful electron flow even if the metal slug was magnetic. "
See more examples of Phil's fakes here.
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Comments (4)
Batteries make better capacitors!!! Only a small charge is required to get the voltage high enough for light and then up to full charge is nearly constant voltage. The capacitor on the other hand charges linearly and unless the LED has a constant current and or an efficient driver, it will vary in brightness. Finally the battery is cheaper than the capacitor by far!
Posted by Tony | April 10, 2008 1:31 PM
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Posted by mgzurydq xynw | September 10, 2008 11:00 AM
Yes there are genuine shake-to-charge torches out there. See my previous post on the subject. At one time there was a photo here somewhere of my torch with coins stuck to the outside, proving the presence of the strong magnets.
There is a very simple test - switch on and shake it. If it is genuine there will be a very obvious increase in LED brightness at each shake.
Posted by John Goldsmith | March 25, 2009 11:29 AM
I have a shake-to-charge flashlight too. It definitely has a capacitor as storage device - I've had it apart. And the magnet is really strong too. After removing it from the drawer where I keep it, I have to peel off paper clips, scissors, screwdrivers, etc. Definitely a thing to keep away from credit cards and cassette tapes!
It takes about half a minute of vigorous shaking before there's enough charge for the LED to even begin to light (which makes sense as the LED characteristic has a 'knee'). After that, you really feel that each shake has an effect.
And yes, even when discharged, there is a momentary flash as the magnet passes through the coil!
Posted by Peter F Vaughan | March 25, 2009 12:38 PM