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Faraday Flashlight...

Discussion in 'Electronic Basics' started by Xtrchessreal, Jan 26, 2006.

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  1. Xtrchessreal

    Xtrchessreal Guest

    You have seen the commercials on TV about the new flash light that
    never dies and needs no batteries?

    Anyone here have one?

    I don't have one but I was wondering about the bulb. It seems likely
    that it is a led or two or three.

    I figure the thing is a coil with a magnet passing through to induce a
    current with a small transformer to turn the current into a high
    voltage whose energy is stored in a large electrolytic capacitor. The
    capacitor is discharged slowly over a resistor and the led/diode in

    Not a bad design but I can't believe the light from it is any better
    than my penlight brinkman. Anyone have one to compare notes with?

    Moving parts will cause something to breakdown quickly if your son
    starts playing with it like a toy - which it basically is right? Good
    toy for the child engineering type perhaps.
  2. Ryan

    Ryan Guest

    I think I know the commercial you are talking about. I don't have the
    same light officially, but basically, the one I have is the same. I
    have the smaller version of a shake flashlight, translucent clear

    Stock, mine came with two CR2032 coin batteries. Cheating, right? I
    took those out to see how long it really lasts. Usually these lights
    come with some form of high capacitance capacitor, either 0.47 farad
    or 1.0 farad.

    After several seconds of pretty hard shaking, mine charges fully. The
    LED (only one) is full bright for about 6 seconds and then I would say
    it is half bright for about 2 minutes. It gets dimmer and dimmer more
    and more slowly after that.

    I can use it around the house to dodge toys and stuff during those few
    minutes. It wouldn't be of much use outside, for example.

    You have to shake it just a little bit hard than you prefer in order
    to make enough voltage to charge.

    I paid $4.00 for it (non retail) so I don't mind for having learned
    about it.

    I also have a 3 LED crank-up light. This one is much more useful.
    Inside this one is not a capacitor, but a lithium (ion?) battery.
    About a minute of pretty good cranking (at least two revolutions per
    second) yields maybe 5 minutes of pretty good light. The first two
    minutes or so are pretty good and then it is noticably dimmer but
    still useful. You can read a book with it for maybe 10-15 minutes,
    depending on who you are.

    This one uses 3 gears of speed increase from the handle and powers a
    small DC motor. Actually, I think it is a stepper motor? There is a
    bridge rectifier inside and you can crank either way.

  3. steamer

    steamer Guest

    --Think about it: "Farad" is a unit of capacitance. Rattle a magnet
    thru a coil and you charge up a capacitor. Cap drains and makes flashlight
    bulb light up; that's all it is. Oh, and they *do* wear out..
  4. Si Ballenger

    Si Ballenger Guest

    I've got one of the origional Russian "forever flashlight" like
    below. Switching to LEDs would probably make it a little more
    functional. Would be interesting to test the new pumper light
    (bottom) against the shaker lights.
  5. Do they go, "Whirrrrr" when you pump them?

    Illuminate your cave and exercise your grip simultaneously! ;-P

    I'm kinda thinking, an aluminum or SCH40 PVC tube, with one of
    these inside:
    and as many turns of #36 ~ 40 wire as you can fit; a couple
    of spongy rubbery pads at the ends, and maybe a supercap -
    I haven't thought it through that far yet. ["No Shit, Sherlock!"
    -- One of my other pesky homunculi]

  6. Yep, they were discussed nearly to death on SED recently.
    One, yellowish-white.
    Pretty much. Magnet, coil, four diodes, .47F supercap, limiting diode
    and LED.
    Bright as hell for the first ten minutes, bright enough to see
    clearly across the street. Unusable for reading large print at about
    twenty minutes, but usable for navigating large obstacles for thirty.
    I got two for US$5 at Wallgreen's. Had two CR3032 coin batteries
    which it works just fine without per Ryan's reply, though mine seem to
    be brighter and last longer than his. These are clones of clones of the
    "Forever Flashlight" as seen on TV mind you, and others on SED reported
    buying fakes with magnets that weren't, coils connected to nothing, and
    bogus circuit boards.

    As for moving parts, the magnet bangs into fairly robust rubber
    bumpers at both ends of its travel, but the switch is made of thin, not
    very springy zinc-plated steel which had to be rebent in one of the pair
    I got before it would come on.

    BTW one survived the "four-foot drop to a concrete floor" test (quite
    accidentally) with no damage or failure.

    Overall, I trust 'em. One is in my toolbox, the other in my wife's

    Mark L. Fergerson

    PS keep the magnets away from any magnetic media you don't want scrambled!
  7. Bill Bowden

    Bill Bowden Guest

    You have seen the commercials on TV about the
    Yes, I got mine from Santa Claus. It's the large version, about a foot
    long with dual coils, rechargable lithium battery, and runs for 10
    hours on a 10 minute shake. I haven't timed it to see if the
    advertising is true, but it runs for a long time on a short shake. It
    has a single white LED that is very bright at 2 or 3 feet. It's a bit
    bulky, weighs almost a pound, and won't fit in your pocket. The magnet
    is strong enough to pick up a 7 ounce pair of pliers.

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