A capacitor stores energy by means of a static charge as opposed to an electrochemical reaction in a battery.
The capacitor works by storing a DC charge between two plates. One of the plates has an insulating oxide layer that is created and maintained when the capacitor is charged up.
It is this insulating oxide layer (called a dielectric) that is crucial to proper capacitor operation.
If the dielectric was not present, the capacitor would short circuit and draw large amounts of current. Applying a voltage differential on the positive and negative plates charges the capacitor.
There are three types of capacitors:
electrostatic capacitor
The electrostatic capacitor with a dry separator is the most basic. This original capacitor has very low capacitance and is used to filter signals and tune radio frequencies. The size ranges from a few pico-farads (pf) to low microfarads (μF).
electrolytic capacitor
The electrolytic capacitor provides more farads and these larger units are used for power filtering, buffering and signal coupling. Rated in microfarads (μF), this type of capacitor has several thousand times the storage capacity of the electrostatic capacitor and uses a moist separator.
super-capacitor
The super-capacitor, rated in farads, which is thousands of times higher than the electrolytic capacitor. The supercapacitor is used for energy storage undergoing frequent charge and discharge cycles at high current and short duration.
The Farad is a unit of capacitance named after the English physicist Michael Faraday. One farad (1 F) stores one coulomb of electrical charge when applying one volt. One microfarad (μF) is one million times smaller than a farad, and one pico-farad (pF) is again one million times smaller than the microfarad.
When large amounts of current flow into a capacitor, it causes the electrolyte solution to boil and turn into a gas. Once turned into a gas, pressure builds rapidly until, hopefully, the safety vent plug releases that pressure.
This rupture can be very dramatic and very destructive. Not only is the boiling liquid and gas very hot, it is also corrosive and will damage any components covered by the solution. Under controlled laboratory conditions, measurements have been taken during a violent, large capacitor rupture. The equivalent explosive force of half-a-hand grenade has been measured.
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