Battery-free flash light

[Lance]

Alright' date=' thanks.

Why's the tube containing the magnet have to be plastic, an insulator?

And Lance, how long did it take to wind the coils? Did you have to tape the coil to the pen tube to make it stay on?[/quote']

 

A metallic tube will shield the magnet/coils and you wont get any voltage. Try googling 'eddy currents', I think that’s related.

 

for the coils you will need to wind each layer then use some type of glue to hold it on. Then wind the next layer on top of that and repeat. Elmer’s glue will work fine but I like using polyurethane varnish.

[5614]

surely if you are not looking for visuals, only the actual job most glues would work for the gluing the coils?

[Lance]

surely if you are not looking for visuals, only the actual job most glues would work for the gluing the coils?

 

Yes. I like the varnish because its fast drying and is strong even with a very thin coat so you can get denser coils.

[psi20]

I did some more research and found

 

"Q: Will dropping a magnet down a long tube of conducting material cause a current in the tube?

 

A: According to Faraday-Lenz law of electromagnetic induction, a current is generated in a closed conducting path (in this case the wall of the tube) if the cross-sectional area defined by the tube is traversed by a variable magnetic flux. The magnet creates a dipole-like magnetic field that will pass through the cross-sectional area of the cylinder, thus defining a magnetic flux. This flux varies in time only when the magnet approaches entrance and enters into the tube, and also when it approaches the exit and exits from the tube. Only during these transient periods of time a current will be induced in the tube. During the time when the magnet travels through the interior of the tube (as assuming that the tube is very long and the magnet is very far from both of the tubes ends) the magnetic flux remains constant and therefore no current will be induced in the tube."

http://www.slcc.edu/schools/hum_sci/physics/tutor/2220/em_induction/

 

I think that means that the coils have to leave space on the ends of the pen tube so that the magnet can have an area where it's not under the coils. I'm thinking I'll have to use some tube other than a pen since the springs on the magnet leave little space for the coils needed.

[Microman171]

This is a long time since this topic was last posted to. Have a look here for a nice shake - N - charge torch Shake - N - Charge

[Thomas Kirby]

I would leave the resistor in because once you get this project going well, the transient currents can go well above the 25 or so milliamps that the LED uses, and even above the 100 milliamps or so of surge current.

[H2SO4]

Could one apply a voltage to the coils, and make a cylinoid that pushes the magnet out?

[Thomas Kirby]

And you can believe me about the resistor. One experiment I did in class was to swing a magnet past a coil. This was just a horseshoe magnet swinging past a coil. It put out enough current to make a flashlight bulb flash brightly. That's over 200 milliamps, maybe more than half an amp.

[Mag]

i just saw a commercial for one of these... pretty nifty.

 

you should definitely do it

[Pleiades]

Check out the NightStar flashlight:

http://www.nightstar1.com/

http://www.webbikeworld.com/flashlight/shake-flashlight/

 

I had a good look at one of these flashlights in a store; it’s pretty big and not very bright. There are small magnets at each end of the shaking tube; they do the same job as the springs YT mentioned. I can’t recall exactly, but I’m pretty sure it uses a capacitor. It uses a white LED.

[calbiterol]

Wouldn't increasing the power of the magnet increase the power output of the coil? In other words, are you using something like a NIB magnet, or something like a common refrigerator-door magnet?

[Alchemist]

lance, have tried transforming the voltage?

You could get the desired amount of volts just by using a small transformer.

[wormholeman]

Even though I see you dont have a battery in the battery-free flash light

and you can get a certain amount of volts which are not enough. Couldn't

you just build a tiny inverter?

 

I dont know just an idea.

[The Thing]

I have a stupid question that I honestly don't know the answer to:

Is it possible to build a flashlight that is powered by body heat? Say you just simply clutch it and the heat from your hand powers the flashlight? I wouldn't expect it to be uber efficient tho...

[wormholeman]

I have a stupid question that I honestly don't know the answer to:

Is it possible to build a flashlight that is powered by body heat? Say you just simply clutch it and the heat from your hand powers the flashlight? I wouldn't expect it to be uber efficient tho...

 

probobley.

[calbiterol]

The answer is, absolutely yes. There are commercially available stirling-cycle engines that are powered from the heat of your hand. Stirling engines work on heat differences. It would be quite possible (in theory) to create a (couple) miniature stirling-cycle engines, throw them in the flashlight, power a generator off of the engines, and then run some high-output LED's from the generator.

 

I must add that the best route would be to put rechargeable batteries in the flashlight, and instead of powering the light off of the self-contained power source, recharge the batteries with the power source. That way, you have constant power independent of the power supply, but the batteries won't need to be replaced unless they lose charge (which happens with ALL batteries eventually, even rechargeable ones).

 

Make sense? If not, feel free to ask questions.

[The Thing]

Say if I were to create a hand-heat-powered flashlight about 20cm long and 5 to 6 cm in diameter, is that enough to power a small incandescent bulb? Or are LEDs the only way to go?

How long would the batteries take to recharge?

[calbiterol]

It's probably best to just use LED's. They're oftentimes brighter (when the flashlight has enough of them), pretty much never burn out, chew less power, and are sometimes less expensive. As far as the size goes, the only thing that matters is the size of the hand that's gripping it. Keep in mind these wouldn't work very well when wearing gloves. And lastly, the batteries will be constantly recharging, so unless you have a very long period of little-or-no-heat (like when being held in a gloved hand), there will be no need to wait to recharge the batteries. Additionally, depending on how it was designed, the flashlight could recharge itself while being stored at room temperature.

 

That's pretty much my string of thoughts.

[The Thing]

Okay, everything makes sense, except...

the recharging during room temperature part.

How does THAT work?

[Lance Cho]

Was this your idea? Cause there's something exactly like this that's sold around the world. I think it's called Ever Light Flash light.

[calbiterol]

Yeah, that was all me brainstorming. Wouldn't have ever thought of it if Lance hadn't posed the question and The Thing mentioned body heat, but that's besides the point.

 

As far as recharging at room temp - there'd have to be a core that was either warmer or colder than the surrounding area at all times. So, on second thought, that might not work so well, unless placed in direct sunlight. I forgot to mention that part. Since sunlight transfers heat, under the right circumstances something like this would recharge through solar power as well.

[The Thing]

Hmm...I know a lot of the "batteryless" flashlights are either shake or squeeze-trigger types. I've never seen or heard of a body-heat flashlight before, which is why I asked. Now to think about it, I'll spend my Christmas building one of those gadgets .

Alright! Thanks a great deal calbiterol! A core that's always hotter eh? A lump of plutonium-238!!! Yea!

Now I need to think of a way to build several VERY small Stirling engines. Any help would be greatly appreciated.

[calbiterol]

A better way of doing it would be this: Have a very thin metal tube as the outside of the flashlight layer (and the thermal conductive layer for the stirling engine) and a pvc pipe as the inside layer. The space inbetween can be the heated chamber of the engine. You might be able to get by with only one stirling if you tweaked it right. Although from an engineering point of view, it would be better to have the smallest expansion chamber possible so that the expansion displaces as much as possible.

[The Thing]

Thanks calbiterol. So should I create one large stirling engine or an array of smaller ones?

I've heard that building a low heat difference stirling from scratch instead of from a kit requires attention to details and you have to work very carefully. Is that true?

[calbiterol]

I believe that's true, The Thing. I have not actually built one myself (it's on my to-do-ASAP list, I'd really like to experiment with them), but I've looked into their construction. I'm a bit of a perfectionist myself, so it would probably come (at least partially) naturally to me, but as far as I'm concerned, web plans give a good place to start, a general idea, but experimentation is, by far, the best teacher.

 

As far as one or an array, I would start with one, just for ease of construction, but it wouldn't hurt to try both. As far as reliability goes, the array would probably be better (but keep in mind this would take up more space). Again, experiment.

 

And by all means, have fun in the process!