Shake Up Flashlights - Impressive Induced Current from Motion

[SockCymbal]

So I got one of those flashlights that you see on TV where you just shake them up and they will work...no batteries. I have to say, its a pretty impressive and it is a good demonstration of an induced current from relative motion between a magnet and a coil.

Anyone else play around with these or take them apart?

 

[sporkstorms]

I laughed so hard the first time I saw a commercial for one of those...
I think it was the first, and only time I'll ever see Maxwell's equations on my tv screen. Truly absurd.

 

[Danger]

I'd never heard of those things until my boss bought one for my 93-year-old mother who kept killing her batteries by leaving the light on. While the light isn't terribly powerful, it works well and is extremely handy. (And I didn't need to take it apart to see how it works because the case is transparent. )

 

[vanesch]

My mother in law offered me one of those things too.
Pretty neat, actually !

 

[Francis M]

They look like a neat idea, and with LED's and better lenses/focusing you can get a good bright beam where you need it. THe only question I have is how long does the light last on a "charge" before you have to shake it again. I personnaly haven't seen them in action for any period of time longer than a few minutes.

 

[DaveC426913]

I bought a few that I'll keep in an emergency kit (or 'Bush DefCon Red' kit, as I like to call it).

I'm always finding flashlights with dead batteries because I use them so rarely. I don't know how reliable these things are though.

 

[Integral]

The one I have takes a couple of minutes of good shaking to get started then requires frequent shakes to keep it going. I don't think you can run it for as much as 5 minutes without a shake. I am not sure if this is typical or just mine, I have had it for over a year so was pretty early in the scheme of shake up flashlights.

 

[Dr. Nick]

Hahaha, I’ve never heard for these flashlights before I’ve read this :) … Almost never, I’ve saw one in some Chinese shop, and I was exalted, what a smart idea :), so salesman started to talk how flashlight is powered by magnetic power :) transferred through this plastic here :), I sad jeah, jeah, and proudly bought one. And of course, I couldn’t find peace until I’ve cracked it, and saw that magnet is really just peace of some nonmagnetic metal, and coil is connected to nothing :). So, it was fake, I went to that salesman just to inform him that lamp is fake, but I didn’t convince him, because his theory doesn’t need wires for that magnet to power up the lamp, and everything is perfectly ok :)

 

[Ba]

I've used one before and it lasted for about 5-10 minutes between shakes. I like them a lot but I haven't actually bought one. I just don't use a flashlight often enough to warrant it.

 

[DieCommie]

the commercial is funny

on part is way over the top...

they show this cop, and he holds up a very small flashlight (AA size) and says "this flash light cost me $200 and has to be recharged every day" wtf? who would pay $200 for a AA flashlight that needs to be recharged every day?


about the light, what's the word on how long it stays lit?

 

[Integral]

I just gave mine a 2 minute shake up to charge it. Within 2 minutes it had dimmed enough to require more shaking.

I see this as more of an exercise machine then a flashlight.

 

[moose]

the commercial is funny

on part is way over the top...

they show this cop, and he holds up a very small flashlight (AA size) and says "this flash light cost me $200 and has to be recharged every day" wtf? who would pay $200 for a AA flashlight that needs to be recharged every day?


about the light, what's the word on how long it stays lit?

I don't know what you're talking about, but I'm almost positive he is talking about a 150+ lumen tactical flashlight. I have one and they are CRAZY... Handheld yet can blind someone temporarily (from close enough, however there are some 500 lumen ones which WILL blind anyone for a little time...)

 

[Integral]

I don't know what you're talking about, but I'm almost positive he is talking about a 150+ lumen tactical flashlight. I have one and they are CRAZY... Handheld yet can blind someone temporarily (from close enough, however there are some 500 lumen ones which WILL blind anyone for a little time...)

Perhaps you are thinking about http://www.surefire.com/maxexp/main/co_disp/displ/pgrfnbr/16/sesent/00" of flashlight. I assure you, since I use them with regularity, they are NOT shakeup. The battries last about 1 hr of continuous use and are quite hot after the continuous use.

 

[zoobyshoe]

There are real ones, fake ones, and in between ones.

The fake ones are cheap and don't even have a real magnet in them. They run off flat button batteries that you can't see unless you open the thing up.

The in between ones have both batteries and a cap that you charge when you shake it. I have this kind. I shorted the cap out to see how much imput it gave to the system and it was noticably dimmer without it, operating just by the batteries. It took quite a bit of shaking to recharge the cap to full charge. As far as I can tell, the cap discharges slowly right into the LED through some resistors. I think this one will become permantly very dim once the batteries are low.

I have never examined a "real" one (advertised on TV), but I suspect they also work by charging a cap that discharges slowly through resistance rather than by charging a battery.

 

[cepheid]

I have a "real" one (not a hybrid with batteries as well). It's pretty good. Half a minute of shaking gives you about five minutes of light, and when it is off it seems to retain charge indefinitely. It's a neat design. Yeah, watch out for knockoffs thsat just have metal slugs and coils of wire in them for show.

 

[zoobyshoe]

Half a minute of shaking gives you about five minutes of light...

That's not bad at all, in my opinion, and is quite an improvement over the squeeze-handle generator flashlights that have to be constantly worked to produce light.

 

[DaveC426913]

... watch out for knockoffs thsat just have metal slugs and coils of wire in them for show.

I wonder if that's what I got for my 10 bucks...

How can I tell the diff?

 

[zoobyshoe]

I wonder if that's what I got for my 10 bucks...

How can I tell the diff?

I bought one of those and it was just a matter of unscrewing one end to get the "magnet" out. Turned out it was just an unmagnetized piece of steel crudely snipped off a rod. It wouldn't attract anything ferrous, and, as someone said, if you check you'll find the coil isn't even connected to anything. You should also be able to find the two flat batteries in a cylindrical plastic case wrapped in electrical tape.

 

[cepheid]

I wonder if that's what I got for my 10 bucks...

How can I tell the diff?

No need to take it apart. If you shake it while the flashlight is on, does the light momentarily brighten each time the magnet passes through the coil? Then it must be real.

If you turn it on and it lights up without you having shaken it, or if you leave it on and it doesn't get dimmer with time, then it would seem to be fake (connected to a bettery, not a capacitor)

 

[Castlegate]

I purchased an smaller cheapo one from wallgreens for $5.00. Granted the light output is quite limited, but i won't stub my toe when using it. I decided to see how long this LED light would glow after a couple minute shake. So I went to sleep on it ... forgot about it until the next night going to sleep, to find the LED still glowing 24 hours later.

 

[zoobyshoe]

I purchased an smaller cheapo one from wallgreens for $5.00. Granted the light output is quite limited, but i won't stub my toe when using it. I decided to see how long this LED light would glow after a couple minute shake. So I went to sleep on it ... forgot about it until the next night going to sleep, to find the LED still glowing 24 hours later.

Yeah, sorry to tell you you have a fake or hybrid one. LED's use the merest trickle of power and it lasted all night going strong like that off of the batteries, I'm sure. I did the same with my hybrid, meaning I let it run all night, before I opened it up and found the battery.