Micro battery charger

[spacifique1]

I`m actually working on a small battery. The battery will be charged by short pulses, not a constant voltage. Any idea for a circuit? The available voltage will be in the order of millivolts. I`m looking for something similar to those found in batteryless watches. :P

[audioguru]

1) What can you power with only millivolts?
2) Are you going to put a few hundred or a few thousand of your batteries in series to make some useful voltage?
3) What are you going to charge your tiny batteries from, a pulsing circuit powered by another battery? ;D

[spacifique1]

I`m currently working on something like the kinetic watches.

[prateeksikka]

hi spacifique,audioguru!
i too have heard about such batteries(basically put to use in watches)
but dont have much information aboit it.It is aslso known that such batteries have very long lives.anything more u know plz tell me too. ::)
prateek

[audioguru]

Hi Prateek,
You spell spacific like a blue-blooded Frenchman!
Check-out www.energizer.com and click on Technical Info. They have tiny button and coin shaped battery cells, some that use lithium. They have a shelf life of at least 10 years and pack a lot of lightweight endurance.
They also have expensive AA size lithium cells (1.5V, most other lithium cells are 3V) that have a very flat voltage over their life and they claim they can take many times more digital pictures than alkaline cells. ;D
 

[prateeksikka]

HI AUDIOGURU!
A BOOK ON PHYSICS BY "RESNICK AND HALLIDAY" SHOWS A CAPACITOR BEING USED IN A MEDICAL DEFEBRILLATOR BY A DOCTOR AND THEN IT EXPLAINS ITS ANALOGY WITH THE SPRING.HOW IS A CAPACITOR DIFFERENT FROM A BATTERY IN OPERATION?
(MORE SPECIFICALLY A RECHARGEABLE BATTERY)
CAN IT REPLACE A CAPACITOR IN CIRCUITS?
::)
PRATEEK

[audioguru]

Hi Prateek,
The choice of using a rechargable battery or super-capacitor (many Farads) depends on their strengths and weaknesses:
1) I have some 1W walkie-talkies that use three rechargable AAA Ni-Cads. Each charge powers them for about 6 hours if I don't transmit much. For the small size and weight of the battery it has a lot of power/endurance. But if I charge them then don't use them for a few months, the batteries are dead and needing a recharge due to self-discharge.
2) I have a telephone answering machine and other items with super-capacitors that hold their charge and therefore power the low-current memory for a very long time. But I don't expect the 1.0 Farad capacitor to power my walkie-talkie for longer than a few seconds.
3) I use rechargable Ni-Cad and Ni-MH batteries in flashlights. They stay bright until the end of the charge because the batteries have a very flat voltage during discharge. I wouldn't use a re-chargable battery as the capacitor in a timer circuit where the time period is determined by the reduced voltage of the capacitor as it sharply drops during discharge. ;D