Figure 1: The basic principle of capacitor
Capacitance
Capacitance defined as the ability of a capacitor to hold the charge of electrons. 18th century Coulombs calculated that 1 coulomb = 6:25 x 1018 electrons. Then Michael Faraday to postulate that a capacitor will have a capacitance of 1 farad when a voltage 1 volt can contain as many as 1 electron charge coulombs. With the formula can be written:
Q = CV ... ... ... ... .... (1)
Q = electron charge in C (coulombs)
C = the capacitance in F (farads)
V = voltage in a large V (volts)
In the practice of making a capacitor, capacitance is calculated by knowing the area of metal plate (A), distance (t) between the two metal plates (thick dielectric) and constant (k) dielectric material. With the formulation can be written as follows:
C = (8.85 x 10-12) (k A / t) ... (2)
Here is a table example of a constant (k) of some simplified dielectric material.
Table-1: Constant dielectric capacitor materials
Table capacitor dielectric constant materials
For an electronic series of practical, farads unit is very large. Capacitors generally available in the market has units UF (10-6 M), nF (10-9 M) and pF (10-12 F). Conversion unit is important to facilitate reading the scale of a capacitor. 0.047uF example can also be read as a 47nF, 0.1nF or other samples with 100pF.
Capacitor Type
The capacitor consists of several types, depending on the dielectric material. For more simple can be divided into 3 parts, namely electrostatic capacitor, electrolytic and electrochemical.
Electrostatic capacitors
Electrostatic capacitor is a capacitor groups are made with a dielectric material of ceramic, film and mica. Ceramic and mica is a popular material and cheap to make small capacitance capacitors. Quantities available from pF to several UF, which is usually for a series of applications relating to high frequency. Groups including film dielectrics are materials such as polyester (polyethylene terephthalate, or known as Mylar), polystyrene, polyprophylene, polycarbonate, metalized paper and others.
Mylar, MKM, MKT are some examples of the trademark name for the capacitor with a dielectric material film. Generally this group of capacitors is the non-polar.
Electrolytic capacitor
Electrolytic capacitor group consisting of the capacitors dielectric materials are metal-oxide layer. Generally capacitor including this group is a polar capacitor with the + and - in the body. Why are these capacitors can have a polarity, is due to the manufacturing process uses electrolysis to form positive kutup negative kutup anode and cathode.
It has long been known for some metals such as tantalum, aluminum, magnesium, titanium, niobium, zirconium and zinc (zinc) surface can be oxidized to form metal-oxide layer (oxide film). Oxidation layer is formed through the process of electrolysis, as in the gold plating process. Metal electrodes are dipped into a solution electrolit (sodium borate) and given a positive voltage (anode) and the solution given electrolit negative voltage (cathode). Oxygen in electrolyte solution and separated mengoksidai metal plate surface. For example, if you use aluminum, it will form a layer Aluminum-oxide (Al2O3) on the surface.
Figure-2: Principles Elco capacitor
Thus successive metal plate (anode), layer-metal-oxide and the electrolyte (cathode) form a capacitor. In this layer-metal-oxide as the dielectric. From formula (2) great unknown capacitance is inversely proportional to the thick dielectric. Metal-oxide layer is very thin, so that the capacitor can be made large enough capacitance.
Because of economical and practical reasons, generally a lot of metal material used is aluminum and tantalum. Materials and the most expensive is Aluminum. To obtain a large surface, this aluminum plate material is usually rolled radially. So in a way that can be obtained large capacitance capacitors. For example 100uF, 470uF, 4700uF and others, which often also called capacitor elco.
Electrolyte materials on Tantalum capacitor is a liquid, but there is also a solid. Called the solid electrolyte, but it is not the solution to be electrolit its negative electrode, but other materials are manganese-dioxide. Thus this type of capacitors can have large capacitance, but became more slender and petite. Also because of all the solid, then their work time (lifetime) to be more durable. This type of capacitor has a leakage current is very small so can be understood why Tantalum capacitors become relatively expensive.
Electrochemical capacitors
One other types of capacitors are electrochemical capacitors. Including these types of capacitors and batteries are the batteries. In fact the battery and capacitor batteries are very good, because it has a large capacitance and leakage current (leakage current) is very small. This type of capacitor types are also still in development for a large capacitance, but small and light, for example for electric car application and mobile phone.
Reading Capacitance
In a large capacitor, capacitance values are generally written with a clear number. Complete with a maximum voltage value and polarity. For example in elco capacitor capacitance is clearly written for 22uF/25v.
Capacitors are small physical size and smaller usually only read 2 (two) or 3 (three) numbers only. If there are only two digits unit is pF (pico farads). For example, a capacitor that reads two numbers 47, the capacitor capacitance is 47 pF.
If there are 3 digits, the first and second number indicates the nominal value, whereas the number 3 is the multiplier factor. Factor in accordance with the nominal rates, respectively 1 = 10, 2 = 100, 3 = 1000, 4 = 10,000 and so on. For example the ceramic capacitor 104 is written, then the capacitance is 10 x 10,000 = 100.000pF or = 100nF. Another example is written as 222, meaning that the capacitor capacitance is 22 x 100 = 2200 pF = 2.2 nF.
Apart from some capacitance other important characteristics that need attention. Usually these characteristics specifications presented by the manufacturer in the datasheet. Here are some of the important specifications.
Working voltage (working voltage)
Working voltage is the maximum allowable voltage that the capacitor can still work well. The electro-mania may have experienced the exploding capacitors due to excess voltage. For example 10uF 25V capacitor, the voltage that can be given should not exceed 25 volts dc. Generally, polar capacitors work on DC voltage and non-polar capacitor works on AC voltage.
Temp Work
Capacitor still meets the specifications if the work at the appropriate temperature. Capacitor manufacturer manufacturers generally make a capacitor, which refers to popular standards. There are 4 popular standards that usually listed in the body such as the C0G capacitors (ultra-stable), X7R (stable) and Z5U and Y5V (general purpose). Complete code is presented in the following table.
Table-2: Code characteristics of capacitor grade I
Code class I capacitor characteristics
Table-3: Code characteristics of the capacitor grade II and III
Capacitor characteristics code class II and III
Tolerance
Like other components, there is a large nominal capacitance tolerance. The above table presents the value of tolerance with codes specific numbers or letters. With the above table the user can easily find out the tolerance capacitors are usually listed accompanies the nominal value capacitor. For example, if a written 104 X7R, 100nF it is kapasitasinya with tolerance + / -15%. At the same time that dikethaui also recommended working temperature is between-55Co to +125 Co. (see table characteristics code)
Insulation Resistance (IR)
Although the dielectric material is a material non-conductors, but there is still a current can pass through. That is, dielectric material also has a resistance. although its value is immense. This phenomenon is called leakage DCL (DC leakage current) and dielectric resistance is called Insulation Resistance (IR). To explain this, here is a series capacitor model.
capacitor circuit model
Figure-3: Model circuit capacitors
C = Capacitance
ESR = Equivalent Series Resistance
L = Inductance
IR = Insulation Resistance
If not given the burden, should the capacitor can store charge for ever. But from the above model, is known to have dielectric resitansi IR (Insulation Resistance) is parallel to the capacitor. Insulation resistance (IR) is very large (MOhm). Consequently, of course, leakage current (DCL) is very small (UA). To obtain a large capacitance is required surface area of electrode, but this will lead to smaller dielectric resistance. Because of the IR is always inversely proportional to the capacitance (C), dielectric resistance characteristics are also presented with the usual amount of RC (IR x C) that the units are ohm-farads or megaohm-micro farads.
Dissipation Factor (DF) and impedance (Z)
Factor dissipation is a big percentage losses (losses) capacitance when capacitors work on frequency applications. This quantity to be taken into account factors such as the application phasa motors, ballast circuit, tuner and others. From the model described a series capacitor series resistance (ESR) and inductance (L). Manufacturers usually meyertakan DF data in percent. Total loss (losses) were defined as the amount of ESR is the percentage of capacitor impedance Xc. Written mathematically as follows:
Factors dissipasi
Figure-4: Factors dissipasi
From the above explanation can be counted a total of impedance (Z total) capacitor is:
Impedance Z
Figure-5: Impendansi Z
Frequency response characteristics considered absolutely necessary especially if the capacitor works at high frequency. To calculate the frequency response unit known as best quality factor Q (quality factor) is not equal to other 1/DF.