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Shake Flashlight Torch

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khaliil

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Hi there.
I'm Khaliil and i'm engineering student. I'm doing this project called Shake flashlight which is using Faraday's Law. I know the basic idea and how it works but i want to add some modification to slow down the drain of the capacitor to allow the LED to light more time…I have an idea but i don’t know to apply it, so can you help me with this please.
My question is:
How can I add a voltage sensor which can measure the voltage of the capacitor and than resets the resistor automatically which is connected 2V LED?

Example
I want to keep the LED 2Volts when the capacitor is fully (I’m using super-capacitor 16v) charged and I’m using resistor to protect the LED. when the capacitor reaches 5V i want the resistor to be 4-3ohm's and maintain the LED 2V(fully bright) but the capacitor reaches 3V, i want the LED to be like 1.6V(start getting dim and dimmer till its full OFF)

I would real appreciate your help:grin:.
With Regards,
Khaliil

 

What you are asking for is called a "constant current" generator, one which adapts is pass element, the resistor in your case, to maintain constant current through it when the voltage varies.
There are ways to do it but the results will be disappointing, if it's a white LED, you need something like 3V across it before it lights up so as the capacitor discharges, it will turn off anyway.
The 0A91 is not a good choice of diode to charge a 10,000uF capacitor, it does have a low Vf which helps but you could easily exceed it's maximum current rating. Consider using Shottky power diodes instead.

Brian.
 

As I understood, basically you need a simple zener regulator to bias the LED. Lets say zener with Vz=3 V then LED will light up when capacitor charge up above 3V. and it is off below that.
 

Thanks for the reply but still you didn't solve or answer my question. i can change the diode to 1N4001 or another type but that will not solve the problem. What i need is a way to reduce the draining capacitor to have more lighting.
 

I still do not think it worth doing but the only solution I can think of is to use a switch mode regulator that can give you a constant current output when the input voltage is anywhere between say 6 and 2 Volts.
The problem you will have is that by the time the LED is no longer illuminated by the stored charge, that charge will also be too low to operate the regulator. It might extend the light for a few seconds but no more.

Brian.
 

How about if i use Buck DC DC Converter? because they results in a much higher efficiency and much less heat. besides that, the inductor stores some energy and later releases to the output..
 

That would be the way to do it (a buck converter IS a switch mode circuit) but remember your only source of energy is the residual charge in the capacitor and the converter trades increased input current for output voltage. As the capacitor loses charge you would be increasing the drain on it and making it discharge even faster.

The inductor only stores charge for one cycle of the converter, this will probably be less than 1/10,000 of a second so you can't use it as a way of prolonging the light.

Brian.
 

betwixt said:
That would be the way to do it (a buck converter IS a switch mode circuit) but remember your only source of energy is the residual charge in the capacitor and the converter trades increased input current for output voltage. As the capacitor loses charge you would be increasing the drain on it and making it discharge even faster.

The inductor only stores charge for one cycle of the converter, this will probably be less than 1/10,000 of a second so you can't use it as a way of prolonging the light.

Brian.
Click to expand...



even if the inductor and the capacitor that i'm using is quite big(i mean in units)....so besides that, any other things in ur mind on how to prolong the light ????
BWT, is there a way to add a vibrating mechanism (instead of shaking by hand) to this torch to help shake the magnet once the ON bottom is pushed.
 
Last edited:

khaliil said:
Hi there.
I'm Khaliil and i'm engineering student. I'm doing this project called Shake flashlight which is using Faraday's Law. I know the basic idea and how it works but i want to add some modification to slow down the drain of the capacitor to allow the LED to light more time…I have an idea but i don’t know to apply it, so can you help me with this please.
My question is:
How can I add a voltage sensor which can measure the voltage of the capacitor and than resets the resistor automatically which is connected 2V LED?

Example
I want to keep the LED 2Volts when the capacitor is fully (I’m using super-capacitor 16v) charged and I’m using resistor to protect the LED. when the capacitor reaches 5V i want the resistor to be 4-3ohm's and maintain the LED 2V(fully bright) but the capacitor reaches 3V, i want the LED to be like 1.6V(start getting dim and dimmer till its full OFF)

I would real appreciate your help:grin:.
With Regards,
Khaliil

Click to expand...

hi friend

better to used supper cap i made a torch and used this technique information can be found here i will share article tomorrow

**broken link removed**

regards
Fragrance
 

I use a similar arrangement in a "squeeze" torch, one with a lever you pull in to the handle to twist a small generator rotor. It still doesn't fix the problem though. The SuperCap works well but you need an external power source to charge it, in a 'shake' torch, the power taken by the LED clamps the generator voltage and limits the charge available to the capacitor. What is needed is something that maintains the 3V or so needed by the LED when the capacitor/cell drops below 3V. My point about it being a futile exercise is that by the time the voltage has dropped below 3V there isn't enough charge left to support a boost converter for long enough to be worthwhile. I have run white LEDs from boost converters running on as little as 0.75V but as the supply voltage drops, the current increases and the charge is exhausted ever quicker.

Brian.
 

Thanks Fragrance for sharing the article. i know and I'm using the super-capacitor idea..even i'm thinking to use two super-capacitors in parallel but i want a way to slow the draining capacitor..it seems that i'm in dead end...any other ideas will be appreciated...
 

betwixt said:
I use a similar arrangement in a "squeeze" torch, one with a lever you pull in to the handle to twist a small generator rotor. It still doesn't fix the problem though. The SuperCap works well but you need an external power source to charge it, in a 'shake' torch, the power taken by the LED clamps the generator voltage and limits the charge available to the capacitor. What is needed is something that maintains the 3V or so needed by the LED when the capacitor/cell drops below 3V. My point about it being a futile exercise is that by the time the voltage has dropped below 3V there isn't enough charge left to support a boost converter for long enough to be worthwhile. I have run white LEDs from boost converters running on as little as 0.75V but as the supply voltage drops, the current increases and the charge is exhausted ever quicker.

Brian.
Click to expand...


Thanks for sharing your ideas betwixt...it's really helpful...
please try to share with me your expertise of making "squeeze torch" as it seems bit mechanical. any idea (mechanically) on how to make the magnet go up and down without shaking it by hand. any idea that can make possible the magnet to vibrate or shake?? I'm thinking to use low voltage stepper motor...even though it will consume the power i'm trying to save for the lighting.
 

Using a stepper motor to turn a generator sounds like a great example of why perpetual motion never caught on.....

My 'squeeze torch' has a handle, like a gun trigger, when you pull it in, a magnet spins inside a pick-up coil and generates the power for the lamp. I modified mine with a schottky bridge rectifier, two capacitors and a white LED. It gives almost as much light as the original filament lamp but it lasts about twice as long.



Brian.
 
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