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Turning supercapacitors into batteries

Hi All,

I have been pondering this for a while ...
If once can make or buy a very beefy supercap say few 100farads,
1. can one treat a supercap with that much storage cap as a battery?
2. if so what circuit can be used to allow the SC to be used as a battery for prolonged discharge

thanks for your help
 
1.yes.
2.generally,you need to charge it and let it supply it's charge to the load

What do you want to use them for?
What load?
What voltage?
 
Thanks - Dorke for your prompt reply,

to be honest - I am thinking aloud at the mo, I have been reading about making SC using activated charcoal in an aqueous solution,
apparently these can be pretty powerful ... me thinking why can't these be turned into batteries,
then I read about the fast discharge properties of caps in general ...
anyway - I though may be someone here can give me some ideas
 
The other thing that distinguishes a capacitor from a battery is the discharge curve. A capacitor will lose voltage linearly as discharged. A battery holds its voltage, or declines at a slow rate up to a point then falls off rapidly. This makes the battery more suitable to power a device requiring constant voltage. But you can get around this with capacitors by using a boost converter, which allows you to maintain constant voltage while extracting a good percentage of the energy from the capacitor.

That said, they are still not practical as batteries is most circumstances since the energy density is far lower. A capacitor that had as much energy as the 18650 cell Colin refers to would be bigger than a breadbox,

Bob
 
Years ago, Coleman (of all people) introduced a cordless screwdriver with supercaps in the handle instead of nicads. It didn't have as long a runtime as the standard Skil model, but it went from dead to full charge in 90 seconds.

ak
 
No. How many?

ak
Depends strongly on the max voltage of the supercap.

Assuming a 5V one, which might be useful for this purpose, and are commonly available:

For the battery, a 18650 cell with 4000 mAH has

4 * 3.7 * 60 * 60 = 53280 Joules of energy

A supercap will have

1/2 C V^2

For 5V we have:

1/2 C * 25 = 53280
C = 53280 * 2 / 25 = 4262 Farads,

And that is if you can extract all the energy from the supercap, which you cannot.

Bob
 
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