> I have an LED torch that gets its power from being wound up. It has died,
> and now won't charge up by winding, well winding produces voltage, but it
> won't retain charge. Had a look inside it, the generator produces about
12V
> when wound, but the capacitor looking piece immediately drops back to
about
> 3V when you stop winding.

Original battery is most likely a NiCd with 3 cells but, as Joe says, many
fakes exist.
A supercap could be used BUT chargeup time is significant until LED can
light.
eg if a supercap was rated at 4V max and LED lit OK at 3V or above, then
due to E =3D 0.5CV^2 you need to charge cap to 3^2/4^2 =3D~ 55% of its capa=
city
before LED lights OK.

12 Voc is OK as current is what counts and battery will clamp alternator to
form a constant current source. EXCEPT if battery charges to full capacity
(unlikely) when voltage will cause problems.

Some lights are outright non-workers with primary cells being used to
simulate crank or shaker action. Others may "try" to charge primary cells -
which may work to some extent in some cases.

Some shakers do work but do not have the energy output levels to operate an
LED well or to charge their battery well.

Most crank lights are liable to be genuine but may be arranged to run on
either LEDs or primary cells without charging.
Crank is electrically not too hard to do so more are liable to be genuine
than shakers. Crank lights tend to be mechanically far less efficient than
is desirable. About 1 Watt out continuous is achievable with the multistage
plastic gear trains often used. Properly done hand power can produce 5 to
10 Watts with less effort than from a 1 W crank or squeeze light.


    Russell
--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.