How much electricity can a capacitor hold?

Question

Is a capacitor like a battery? For instance, is there a short burst, or a stored amount that is slowly discharged?

I was wondering if small windmills/ fans/rotors, maybe attached to the back of a moving car, could provide enough energy to be useful somehow. Would a sustained 120volts be possible for a short time? How can we make use of movement, even if its in small amounts, like air blowing into a moving cars engine compartment as usual, but have it turn a fan motor located inside, which would be hooked to a capacitor. The fan shouldnt cause any power loss because it wouldn't have drag, and could even be useful in cooling off the engine. It just seems like there is wasted potential and energy out there.

Answer 1

To be specific, a capacitor stores charge.  The rate that an ideal capacitor is discharged is entirely dependent on the circuit it is connected to.  An equation that describes the electrical behavior of a capacitor is I=C*(dv/dt) where I is the current into or out of the capacitor (think of current as the movement of charge), C is the rated value of the capcitor (a measure of how much charge it can store) and (dv/dt) is the rate of change of voltage across the capacitor.

While it would be possible for an appropriately constructed capacitor to be charged up to 120v.  It would only sustain 120v as long as no current was flowing.  In order to make use of the energy in the capacitor, charge must leave the capacitor, thus current must flow and the voltage will change.  In practical circuits, a capacitor that needs to store energy in this way would need to be chosen with a large capacitance (storage capability) that the change in voltage when current is flowing is acceptably small for the given application.

The key difference between a battery and a capacitor is that a capacitor stores energy strictly in an electric field while a battery stores energy chemically.  In general,  more energy can be stored in a battery of a given weight, volume, and cost, than in a capacitor of similar proportions.  Also, real world, non-ideal batteries and capacitors slowly dissipate energy through internal paths even when energy current is not flowing out of the device to do meaningful work.  Again, batteries typically outperform capacitors in this aspect of storing energy, although new technologies are constantly being studied for energy storage in both types of components.

Answer 2

A capacitor is similar to a rechargable battery in the way it works.  The difference is that a capacitor can only hold a small fraction of the energy that a battery can.  (Except for really big capacitors like the ones found in old TVs.  These can hold a lot of charge.  Even if a TV has been disconnected from the wall for a long time, these capacitors can still make lots of sparks and hurt people.)  As with a rechargable battery, it takes a while for the capacitor to charge.  So if we have a 12 volt supply and start charging the capacitor, it will start with 0 volts and go from 0 volts to 12 volts.

Answer 3

Essentially a capacitor is similiar to a battery. It stores electricity and releases it at a continuous voltage like a battery. The only thing is is that capacitors are used to help regulate the amount of power......they store electricity but dont hold a "charge" for as long as a battery could. They need to be charged, disharged, and recharged.....over and over again.