# can a pop bottle capacitor store a charge for long periods of time?

I built a capacitor with tin foil salt water and a pop bottle and i was wondering if i could build one that would store a charge for a while, not just a fraction of a second.

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Jack A Lopez7 years ago
This is an interesting question.

An ideal capacitor can hold a charge forever, which means if your capacitors are not staying charged, then they are somehow less than ideal.

But why is this? Where does the charge go? A charged capacitor also contains stored energy. This means energy is going somewhere, or perhaps changing to another form somehow.

Everything goes somewhere. That's what sensei used to say. He was always asking these sort of Zen-Gedanken questions intended to make us think more deeply about the physical world. Stuff like: If you take a metal spring, and then compress it so as to make the spring fit into a small box, and then imerse the box and spring together into a vat of mineral acid, so that the spring is completely disolved, then what happens to the energy you put into compressing the spring?

Usually the answer was heat. When you couldn't figure out where else the energy could possibly be going, heat was usually a good guess.

And I am guessing that is where the missing energy in your homemade capacitors is going. Somehow it is turning into heat.

Moreover I will guess that this heat is Ohmic in nature, that is to say due to electric current flowing through some sort of resistance. Perhaps current is slowly oozing its way through an imperfect dielectric, or maybe even moving through the air or space surrounding the capacitor. Although I cannot say with certainty which of these is the case for your homemade capacitors.

If you like, you may think of this resistance as a lumped ideal resistance, as R, just as you may think of the capacitance as a lumped ideal capacitance, as C. This guesswork is summarized in the pretty picture below.

With R anc C tied together this way, the answer to "how long" is simply the time constant R*C. That's how much time it takes for the voltage, or charge (Q=CV), on the capacitor to fall to 1/e its previous value.
73lonestar8 years ago
hey all i am a tech and i can say that their is so many different sizes of can capacitors and the only ones able to store a large charge with a good current is large caps between 15.000 micro farrid and 2 farrid can even think of some type of free energy hhhhhhhmmm?
toelle8 years ago
There should be a way since regular capacitors can store electricity for months!
NikonDork8 years ago
Leyden Jars will hold a charge for a few minutes. As long as your using the proper materials.
NachoMahma8 years ago
. I'm guessing that PET isn't a good dielectric. Try using glass. . Using foil on the inside, instead of an electrolyte, might help.
XOIIO8 years ago
I don't think there is a way, you can try different materials, but it moight only lenthen the time for a second.