Ultracapacitors

Ultracapacitors are capacitors that can store so much charge that they are beginning to blur the functional distinction between the capacitor and the battery. Indeed, some of the most impressive ultracapacitors are rated at 5000 farads and are sized just bigger than a half-liter soda bottle. Ultracapacitors have just recently started to show up in products as alternatives to batteries. Theoretically, ultracapacitors have many benefits that make them a potential replacement for batteries. For instance, ultracapacitors can put out much more power for a given weight, can be charged in seconds instead of hours, and can function at more extreme temperatures. In addition, ultracapacitors are more efficient and have a longer lifetime due to the greater number of discharge cycles compared to that of batteries. This makes ultracapacitors ideal for devices that need to be sealed for long periods of time. On the down side, ultracapacitors are still really expensive, and they don't have the energy density of batteries.

To understand how ultracapacitors work, it is helpful to review the basics of how capacitors work. So first, we'll look at the basics of capacitors, then look at how ultracapacitors differ, and finally go over some of the current applications of ultracapacitors in society today.

Capacitors

Dielectric

Basically, capacitors are a circuit component that stores electric charge. Another way of putting it is that capacitors store energy in an electric field created by two different conducting surfaces charged with equal but opposite charges. Positive charges collect on one surface and negative charges collect on a second surface nearby, but a key point is, the charges are on electrically separate surfaces. Typical capacitors consist of two plates that act as the conducting surfaces. These plates are called electrodes. The plates are separated by an insulator or dielectric, which help create a high capacitance in the capacitor due to the polarization of the molecules in the material. One way ultracapacitors differ from capacitors is that they are not separated by an insulator or a dielectric in the same sense as a typical capacitor, which will be discussed in more detail later. Since the plates of a capacitor are conductors, the charge is stored on the surface of the plates, and since each plate is charged with an equal but opposite charge, the net charge on a capacitor is zero. The property of a capacitor that allows it to hold charge is called capacitance.

Capacitance

Capacitance is the property that allows a capacitor to store charge.