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tightsocks · Oct 19, 2006, 06:40 PM

Ever see those flashlights that work by shaking them to move a magnet through a bundle of copper wiring...?

Well, I was all excited today to find a generic brand of them at the dollar store, so I got a couple of 'em.

When I was playing with it back at home I noticed that it would light-up even without shaking it, and that the bulb seemed much brighter than the name brand ones that I had seen before.

I opened it-up and found two 3 volt lithium button batteries hidden behind the switch...!

turtle777 · Oct 19, 2006, 06:41 PM

So what does it do when you shake it ? Play music ?

-t

King Bob On The Cob · Oct 19, 2006, 06:44 PM

Well, it has to store the power you generate by shaking it somewhere...

I'm assuming the lithium batteries are rechargeable?

Rumor · Oct 19, 2006, 06:44 PM

That's what happens at the dollar store. They aren't true kinetic energy powered flashlights.

turtle777 · Oct 19, 2006, 06:48 PM

Originally Posted by King Bob On The Cob

I'm assuming the lithium batteries are rechargeable?

Uhm, no.

Do you really think that the dollar store will sell a true kinetic flashlight that even includes rechargable batteries ?

It's a fake, nothing else.

-t

tightsocks · Oct 19, 2006, 06:56 PM

The batteries are probably worth more than the $2.00 price of the flashlight...

slpdLoad · Oct 19, 2006, 07:10 PM

I found one of those flashlights on display at a local hardware store, but I could never get it to light up. Then again I didn't try for too long as I felt rediculous standing in a store flailing this flashlight about trying to make it do something.

olePigeon · Oct 19, 2006, 07:20 PM

Originally Posted by slpdLoad

I found one of those flashlights on display at a local hardware store, but I could never get it to light up. Then again I didn't try for too long as I felt rediculous standing in a store flailing this flashlight about trying to make it do something.

Nice sig.

vmarks · Oct 19, 2006, 08:16 PM

I bought the four pack of those. I figure if power blips out, I won't have to fuss over dead batteries.

Takes about a minute of shaking to get enough of a charge to keep the light on.

Of course, I prefer my Maglite, but the faraday shake jobs will do the trick when needed.

slpdLoad · Oct 19, 2006, 08:51 PM

Originally Posted by olePigeon

Nice sig.

It was on sale.

hayesk · Oct 19, 2006, 08:58 PM

Originally Posted by what_the_heck

Uhm, no.

Do you really think that the dollar store will sell a true kinetic flashlight that even includes rechargable batteries ?

It's a fake, nothing else.

It could be fake, but the kinetic flashlights have to store the power somewhere. Where do you think a true kinetic flashlight stores its power?

SSharon · Oct 19, 2006, 09:02 PM

Have none of you ever seen the calculators with fake solar panels?

ghporter · Oct 19, 2006, 09:05 PM

They store energy in a capacitor. Capacitors that can store the amount of electricity needed to make an LED like that light up for any appreciable time are cylindrical, and generally about 2cm in diameter by 2-5cm long.

Please don't think that kinetic energy flashlights are anything super high-tech cool; they're very simple devices. Slide a magnet through a coil of wire and you WILL produce an electric current thorugh the coil. With a few diodes and that capacitor I mentioned, you could make all the circuitry needed for one of these for pennies.

But the lithium-battery thing is almost certainly fake unless there's also a big ol' capacitor in there too.

Eriamjh · Oct 19, 2006, 09:16 PM

So did it work without the batteries?

Buckaroo · Oct 19, 2006, 09:34 PM

100 LED Flashlights on ebay are great. It goes a long way on AA batteries.

tightsocks · Oct 20, 2006, 09:49 AM

Originally Posted by Eriamjh

So did it work without the batteries?

Nope!

There is no capacitor in it and the copper wire bundle is just for show. In fact, there is just one thin ring of copper and none of the supposed kinetic mechanics are connected to the battery, or anything at all for that matter...

I took out the lithium batteries and put them in an old Casio organizer I had sitting around.

Eriamjh · Oct 20, 2006, 11:07 AM

I was wondering how they could sell those LED lights for $20 in one place, and $3 somewhere else. I guess it never occurred to me that they are fake.

Sky Captain · Oct 20, 2006, 11:08 AM

I have a true kenetic flashlight I keep in my flight bag.
I've had it dead dead dead. Shook it for about 30 seconds and it lit up for a few minutes.
It has a capacitor circuit to a rechargable battery.

Millennium · Oct 20, 2006, 11:13 AM

I suppose that is is, in theory, possible to put a rechargeable battery into a flashlight like this to store the energy from the shaking. It would depend on whether the coil/magnet combination could generate enough power for the batteries to store at all.

However, even if this worked, it would be a very poor solution compared to the capacitor-based setup that "real" flashlights of this type use. Aside from the problem of getting the power high enough for the batteries to store in appreciable amounts, the fact that most users don't shake the flashlights for very long means that the memory effect on the batteries would be horrendous. Capacitors don't have this problem, which is why they work so much better for these lights.

My guess is that the dollar-store versions of these lights don't take this into account, and are therefore best considered fakes. Even if they actually did function as advertised, the quality is so poor that they'd cease to function long enough to be useful for very much after only a few cycles.

ibookuser2 · Oct 20, 2006, 12:46 PM

There are actually two variants of the cheap dollar store kinetic flashlights. One has the two lithium CR2032 cells which are wired directly to the switch and LED. The coil is soldered to the small circuit board, but there are no rectifier diodes on the board so it's connected to nothing. The "magnet" is just a hunk of scrap metal; not in the least bit magnetic.

The other variety looks nearly identical on the outside, but instead of the two CR2032 cells, there's a small NiCd battery soldered to the circuit board, and the rectifying diodes are present, and the magnet is actually a magnet. In theory, shaking the flashlight does charge the battery, but it would take an eternity to actually charge the NiCd battery with the pathetic coil that's in these things, so they're not really useful once the NiCd has lost its initial charge.

Both versions are more or less disposable flashlights and the shaking is just a gimmick. But at least they're useful until the batteries die.

tightsocks · Oct 20, 2006, 12:55 PM

Originally Posted by ibookuser2

There are actually two variants of the cheap dollar store kinetic flashlights. One has the two lithium CR2032 cells which are wired directly to the switch and LED. The coil is soldered to the small circuit board, but there are no rectifier diodes on the board so it's connected to nothing. The "magnet" is just a hunk of scrap metal; not in the least bit magnetic.

Yup.
This sounds just like the one that I have. Except that the copper coil isn't connected to anything

In spite of all this, the packaging says, "Just Shake - No Battery Needed"

turtle777 · Oct 20, 2006, 01:20 PM

Originally Posted by tightsocks

In spite of all this, the packaging says, "Just Shake - No Battery Needed"

Yeah, that should have read

"Just Fake - No Shakery Needed"

-t

hayesk · Oct 21, 2006, 02:56 PM

Originally Posted by ghporter

They store energy in a capacitor. Capacitors that can store the amount of electricity needed to make an LED like that light up for any appreciable time are cylindrical, and generally about 2cm in diameter by 2-5cm long.

Fair enough. I figured capacitors small enough to fit in a flashlight would discharge too quickly.

I have a wind up flashlight that does have a rechargeable battery. Though it was $50, not $3.