# "Shake flashlight" how strong (current, volt)?

Discussion in 'Electronic Basics' started by Lou, Jun 12, 2004.

1. ### LouGuest

Hello, I'm new to electronics. I want to make a small device with a small
6V motor and no batteries. I want to use the "shake" system, which can be
found in some fun flashlights. (see link: http://www.quality-items-
flashlights.com/product_info.php?products_id=90 ).

Only I am not sure how much power such a "shaker" can provide.

I want to power a little fan with blades of say 12 centimetres wide
(diametre, 5 inches), to make wind.

I would appreciate it very much if someone could explain to me how much
shaking you would need, to power the fan for about 3 minutes.

And I would also like to know if I use "two" magnet shakers, do I increase
the power 2 times? Or is there loss?

Thank you very much!!

(Sorry for my English, I'm a french school student, American friends I hope
you don't mind! )

heres a build it yourself version

http://www.creative-science.org.uk/gensimple1.html
not a lot, always allowing for conversion efiicency less than you put in.
not enough power, all the shake lights I have seen use LEDs for their very
low power consumption.
Very vigourous for the full 3 mins unless you store the nergy, shake lights
sometimes use a Capacitor as a form of tiny battery so they will light after
you stop shaking.

Fan uses lots, relative to an LED , of power, lighting things up is easier.
using two identical units wired together would giove you twice the power and
take twice the effort to shake.
Your English is excellent, far better than my French and we speak English
even in Scotland ;-)

HTH

3. ### js_530Guest

..00425 watt hours from 30 seconds of shaking. A small DC motor might
use 6 volts at 100 milliamps, or .6 watts. To power it for 3 minutes,
you would need 3.5 minutes of shaking (I think....?) Maybe you
could find a smaller motor, or use two shakers. Another issue is
current limiting. If you accidently stopped the fan blade, current
would easily flow through it, draining the charge.
You will make it twice as hard to shake, but not exactly twice as
powerful.

4. ### Rich GriseGuest

In other words, you might as well wave a piece of cardboard.

Cheers!
Rich

5. ### Don KlipsteinGuest

I would advise to use green LEDs having either peak or dominant
wavelength anywhere from 505 to 540 nm.

I would also advise that most such LEDs of "regular size" (5 mm AKA
T1-3/4, 3 mm AKA T1, smaller sizes, including similar smaller surface
mount packages, and even other sizes neither including a heatsink or a
"partial heatsink" nor requiring heatsinking, and questionable as to "high
flux" units in "spider" (4-lead) or "TopLed" packages or the like) tend to
have higher efficncy at lower currents, such as a few milliamps.
Blue, blue-green, white and green LEDs having rated current 350 mA or
more, in my experience, tend to have higher efficiency when somewhat
underpowered.

I would also advise charging of large capacitors for energy storage.
Along with lowest possible current through the LEDs from energy storage
capacitors, even if as low as a fraction of a milliamp. I would avvise
usage of blue-green or green LEDs having peak or (this i different)
dominant wavelengths anywhere around 500 to 540 nm.

I have found ability of LEDs having nominal wavelength close to 500 nm
being able to illuminate a whole room well enough for me to navigate by
using night vision even when said LED was fed 50 microamps and hyad at
this current a voltage drop of only about or maybe a little less than 3
volts.
400's and lower 500's of nm, and also most LEDs having peak wavelength in
this range (and many other LEDs) having peak emissionn wavelength varying
a little notaceably slightly inversely with current.

Wavelength noticeably varying inversely with current I have found to
occur mainly with LED chip chemistries favoring higher efficiency at lower
currents. When the chip chemistry favors higher efficiency at higher
currents (a large majority of those with peak wavelength yellow-green 555
nm or longer, including most yelow, many orange, many red and a few
infrared chemistries), the peak wavelength in my experience tends to
vary less with current.

- Don Klipstein (, http://www.misty.com/~don/index.html)