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flashlight with no batteries

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cowboytuna

New Member
hi guys! have u seen those flashlight with no batteries? they say it gets it power from induction and capacitors. sorry im a newbie and i really want to build one as a project. they are sold here (im from the Philippines) in a really high price. hope somebody could help me with the components' specification and how to build it. thanks in advance.
 

cowboytuna

New Member
ok, ive found that this is a reapeted post. sorry for that, but the older post doesnt answer the question on how to build one. hope somebody could help. pls?

heres a link of the flashlight im talking about. its quite expensive when these are sold here: http://www.flashlight-forever.com/
 

panic mode

Well-Known Member
It looks like magnet that can move inside tube when shaken.
You also have coil fixed arround the middle of the tube which
creates AC power when magnet flies by.
The text mentiones white bright LEDs as source of light.
This makes sense because LEDs are much more energy efficient.
I'd try to use maybe 4 of them wired in series.
I think I can see some electronics too. I would simply use just
the tiny bridge rectifier, relatively large el. capacitor and simple
constant current circuit for the LEDs.
The constant current circuit is easily made using resistor and some
active component. I would just use small LM317L with fixed
resistor of 56Ohm. That should give ca 1.2V/56Ohm=21.4mA.
 

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cowboytuna

New Member
thanks!! but what type of LED? is it the one that is used on cellphone backlight? or the one found on old car stereo. sorry im really new. but i think its the LED used on cellphone backlight? m i right? or is it another type of LED?? hope u could reply again.


thanks again. sorry for my dumb questions but i dont know somebody i can ask.
 

cowboytuna

New Member
also whats LM317L? what type of wire should i use on the coil and how long should the coil be? i hope u could help me. pls.


should i put the circuit that u posted here before the LEDs or before the coil? i would really appreciate ur help. tnx in advance!
 

McGuinn

New Member
OK, get back to basics...
First, the coil acts like a transformer, when a magnet is moved within it, it generates a current. This current will be alternating because the magnet will be moving in two directions. Hence you need a rectifier to control and change that alternating current into direct current...
Then you need to store it... a capacitor does this.

Have a look in Google for the LM317L. You will get what's called a PDF 'datasheet' on the device. The thought behind the LM317L is that it will allow the required current pass into the LED (around 20mA) and prevent a surge, because it will be very hard to control the voltage in this device!

So it goes:
COIL -> Bridge Rectifier -> Capacitor -> Current control -> LED.

The Capacitor will have to be very large, maybe 10,000uF and this may only provide 10 seconds of power to the 4 LED's if fully charged!

The bridge rectifier will ensure that no current is wasted, unlike a half or quarter wave rectifier.

Hope this helps...
 

cowboytuna

New Member
ok. thanks so much. that really did helped. one last question, why does it only last for so seconds while the commercially available ones last longer? did they put something else.


i really appreciate ur post. thanks so much.
 

McGuinn

New Member
To be honest, I'm not sure. The maths may work out differently...
I think you will have to play around with it to see. More capacitors will increase the time, but the coil will have to be quite efficient.

I haven't seen one of these things. How many shakes do you have to give it, and how long does the light last?
 

panic mode

Well-Known Member
They probably use even larger capacitor. Some things like one of
my multimeters do not have bateries. They use capacitors in farad range
(not micro or milifarad). However, most of the supercaps I've seen are
for low voltage. Maybe they use OLEDs so current consumption is lower,
although I dont remeber seeing white ones.
 

cowboytuna

New Member
it needs 30sec of shakes or 3shakes per second or 90shakes in particular. they say it would give u 20 minutes for light with 30 seconds of shake. thats why im a bit surprised that it can only last for 10 seconds. got any other ideas??

the site also says that there are opposite magnets at each end which are align to repel the moving magnet.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
The formula for working with capacitors is C=I*T, where C is the capacitance in Farads, I the current in Amps, and T the time in Seconds.

So for 1200 seconds, at 1A, you would need 1200 Farads. Even at 10mA you would need 12 Farads.

It would be interesting to take one of these apart and see what's inside it!.
 

plot

New Member
McGuinn said:
The site gives us a picture of one of the lamps:
http://www.nightstar-flashlight.com/clear-nightstar-flashlight.html

Note the size of the coil in the body of the unit, and a lack of visable caps!

IMHO, it's a very sloppy website...
odd... it's gotta have caps somewhere to hold the charge, maybe they snuck them inside the coil somehow?

...now i'm really interested in how this works. hrm...

edit: ok, check out the brochure from the website, shows location of parts on the flashlight
http://www.nightstar-flashlight.com/nightstar-brochure.pdf
from brochure:
With only one moving part, NightStar transforms motion into light. Simply shaking NightStar for 30 seconds provides more than
20 minutes of excellent illumination. When shaken, a high strength magnet generates electrical energy as it passes through a wire
coil. Magnets oriented to repel the charging magnet are mounted at both ends of the flashlight. NightStar’s patented Mag-Lev
recoil system smoothly rebounds the charging magnet back through the coil, efficiently transforming motion into electrical
energy. The energy generated is stored in a capacitor. Superior to a battery, the capacitor will never corrode, can recharge
several hundred thousand times and will power the LED even under extreme hot and cold temperatures. Equally impressive,
the LED used in NightStar is practically unbreakable and has a rated lifetime of tens of thousands of hours. The full spectrum
light from the LED is projected into a uniform beam by a specially designed lens and reflector. NightStar also has a unique
magnetic switch, which is reliable, watertight and non-sparking.
 

Optikon

New Member
McGuinn said:
OK, get back to basics...
First, the coil acts like a transformer, when a magnet is moved within it, it generates a current. This current will be alternating because the magnet will be moving in two directions. Hence you need a rectifier to control and change that alternating current into direct current...
Then you need to store it... a capacitor does this.

Have a look in Google for the LM317L. You will get what's called a PDF 'datasheet' on the device. The thought behind the LM317L is that it will allow the required current pass into the LED (around 20mA) and prevent a surge, because it will be very hard to control the voltage in this device!

So it goes:
COIL -> Bridge Rectifier -> Capacitor -> Current control -> LED.

The Capacitor will have to be very large, maybe 10,000uF and this may only provide 10 seconds of power to the 4 LED's if fully charged!

The bridge rectifier will ensure that no current is wasted, unlike a half or quarter wave rectifier.

Hope this helps...
Some energy conserving tips:

If you use a bridge recitifier, use schottky diodes. less drop for given current = less power loss.

Since, you will have to use huge electroolytic cap for the storage, pay attention to leakage specs - some leak less than others and that will be important for the amount of time, your LEDs will glow.
 

petesmc

New Member
I've one of these at home which is broken now. I can rip it apart for you guys and take some pictures if you want. Just gotta find it!

-peter
 
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