Capacitors

Capacitors hold an electrical charge for a predetermined amount of time. Most capacitors are made from a pair of conductive elements separated by an insulating dielectric. This dielectric can be composed of many materials including; air, paper, epoxy, plastic, and even oil. Most capacitors actually have many layers of conducting elements and dielectric.



Capacitors are rated by their capacitance, in farads, and by the breakdown voltage of their dielectric. The farad is a rather large unit of measurement, so many capacitors are rated in microfarads. A microfarads is the equivalent of one millionth of a farad (1/1000000 of a farad), an even smaller rating is the picofarad which is the equivalent of a millionth of a millionth of a farad (1/1000000 of a microfarad). The micro in the term microfarad is most often represented by the Greek mu (μ) character. The picofarad is shortened to pF. The voltage rating (absolute maximum voltage) is the highest voltage that the capacitor can withstand before the dielectric layers in the component are damaged.

Capacitors are classified by the dielectric material that they use. The most common dielectric materials are aluminum electrolytic, tantalum electrolytic, ceramic, mica, polypropylene, polyester (or mylar), paper and polystyrene. The dielectric material used in a capacitor partly determines which applications it should be used for. The larger electrolytic capacitors, which use an aluminum electrolyte, are suited for such chores as power supply filtering, where large values are needed. The values for many capacitors are printed directly on the component. This is especially true with the larger aluminum electrolytic, where the large size of the capacitor provides ample room for printing the capacitance and voltage. Smaller capacitors, such as 0.1 or 0.01 μF mica disc capacitors, use a common three-digit marking system to denote capacitance and tolerance. The numbering system is based on picofarads, not microfarads.

Example: 104 means 10 followed by four zeros, which is 100000 picofarads
Values over 1000 picofarads are most often stated in microfarads. To make the conversion, move the decimal point to the left six spaces. Values under 1000 picofarads do not use this numbering system. Instead, the actual value in picofarads, is listed.

One mark found almost exclusively on larger tantalum and aluminum electrolytic is a polarity symbol, most often a minus (−) sign. The polarity symbol indicates the positive and/or negative lead of the capacitor. If a capacitor is polarized, it is extremely important that the proper orientation is applied when the capacitor is installed. If the polarity is reversed between the positive lead (called the anode) and the negative lead (called the cathode) than the capacitor may be ruined. The results may be as minor as a small “pop” followed by a wisp of smoke, or as catastrophic as a loud bang and a small fire. Other components in the circuit may also be damaged.

Capacitor color codes:
Color
First band (A)
Second band (B)
Multiplier (C)
Tolerance (D)
Black00120.00%
Brown11101.00%
Red221002.00%
Orange3310003.00%
Yellow44100004.00%
Green551000005.00%
Blue6610000006.00%
Violet77100000007.00%
Gray881000000008.00%
White9910000000009.00%
Gold0.15.00%
Silver0.0110.00%
(no color)20.00%


Electrolytic capacitors
Electrolytic capacitors usually have their maximum voltage rating and capacitance value printed right on them, with no codes to interpret. These types of capacitors are polarity sensitive and can explode if improperly installed. In order to determine the polarity look for a mark near one of the legs of the component. Large electrolytic  capacitors have a stripe down the side of the body near one leg that identifies “negative”. These type of capacitors also have a tendency to leak their stored energy.



Tantalum capacitors
Tantalum capacitors usually have their maximum voltage rating and capacitance value printed right on them, with no codes to interpret. Many of these types of capacitors have a stripe marked with a ''+'' sign near it that runs down near one of the leads, the lead indicated by the stripe is positive. Tantalum capacitors are polarized and an improper installation may result is a catastrophic failure.

Aluminum capacitors
Aluminum capacitors work using a dielectric composed of a thin layer of aluminum oxide. They contain corrosive liquid and can burst if the capacitor is connected backwards. The electrolyte will tend to dry out in the absence of a sufficient rejuvenating voltage. These capacitors have a tendency to fail over time and are somewhat high maintenance because of that.

Monolithic capacitors
Monolithic capacitors are not polarity sensitive. Most monolithic capacitors are labeled in a numeric fashion. Monolithic capacitors can have numbers on both sides, one side being the size code, and the other side being the date-of-manufacture code.

Example: a monolithic capacitor labeled ''104'' on one side and ''941'' on the other. The ''914'' refers to the year and week of the manufacture (1999, week 14). The ''104'' refers to the size value which in this case is 0.000094μF. The capacitance number code usually includes three numbers, with the first two representing the value of the capacitor on picofarads and the third being the multiplier (the number to multiply the first two numbers by ten to what power).

Mica capacitors

Mica capacitors are high precision, stability and reliability capacitors. They are available in small values, and are mostly used at high frequencies and in cases where low capacitor leakage is undesirable. They use sheets of mica as the dialectic. The mica is sandwiched together and clamped between sheets of copper foil. These capacitors have notably low tolerance and stability compared to other capacitors which is caused by imperfections in the mica surface which is difficult to manufacture so that it is perfectly flat and smooth. Mica capacitors are now considered obsolete.

Paper capacitors

Paper capacitors are made of flat thin strips of metal foil conductors that are separated by waxed paper. The waked paper is used as the dielectric. Paper capacitors usually range in value from about 300 picofarads to about 4 microfarads. The working voltage of a paper capacitor rarely exceeds 600 volts. Paper capacitors are sealed with wax to prevent the harmful effects of moisture and to prevent corrosion and leakage.

Polypropylene capacitors

Polypropylene capacitors bear a notably high voltage rating, current and/or power performance. These capacitors are based on metallized film or film-foil dielectric types. Polypropylene is generally selected for its excellent dielectric characteristics (losses, absorption, dielectric strength, insulation resistance).

Polyester (Mylar) capacitors

Mylar capacitors are typically very stable and able to operate over a wide range of temperatures, usually up to 125 degrees Celsius. Mylar is a high temperature polyester film the which is used as the dielectric in these capacitors. There may be various shapes, sizes and styles of construction but possibly the longest lived and most recognizable style is the green or brown resin-dipped radial type, which coupled with a small physical size makes it readily suitable for circuit boards.

Polystyrene capacitors
Polystyrene Film capacitors are noted for their exceptionally high insulation, low leakage, low dielectric absorption, low distortion and excellent temperature stability. In most instances polystyrene capacitors can be used as a direct substitute for silver mica and/or ceramic disc capacitors.

Supercapacitors
Supercapacitors (supercaps) are usually measured in full farads or fractions of farads, at a low voltage. Supercapacitors take longer to charge than regular capacitors but hold their electrical charge for a longer amount of time.

Internal impedance is the property of a capacitor that governs how quickly it can be charged and discharged. Some supercapacitors, although they can hold great amounts of voltage, can only release a small portion of their total charge at a time.

Ceramic capacitors

Color codes for ceramic capacitors:

Color
Decimal Multiplier (C)
Tolerance above 10pF (D)
Tolerance below 10pF (D)
Temperature Coef ppm/°F (E)
Black12020
Brown101-30
Red1002-80
Orange1000-150
Yellow-220
Green50.5-330
Blue-470
Violet-750
Gray0.010.2530
White0.1100.1500

Ceramic disc capacitors are usually labeled. If the number is < 1 then the value is in picofarads, if > 1 the value is in microfarads. The letter R is sometimes used as a decimal.
Example: 4R7 is 4.7



VALUE
Capacitor Types and colors:






1pf - 1800pf  Yellow Ceramic Disk or Blue or Yellow Monolithics 
.001; .01; .022; .047; 0.1; 0.47; 1uF (C96 on K2)  Red Monolithics 
Temperature stable caps are marked "NP0", "C0G" or have a black top.


Capacitor Marking Table (Ceramic and Monolithic Cap's)
IMPORTANT: Capacitors with values below 100 pf may be marked two ways: Either with just two digits (22 pF = "22") or three digits (22 pF = "220",).  In the latter case the third digit signifies the number of zeros following the first two digits. "220" = 22 pF, "221" = 220 pF,  "222" = 2200 pF.






VALUE
MARKING
VALUE
MARKING
VALUE
MARKING
1pf; 3pf; 5pf 
1; 3; 5
2.7, 3 or 3.3 pF can be interchanged with each other.
4.7 or 5 pF can be interchanged with each other.
10 pf
10 or 100

0.001 uF
102 

0.10 uF
104 
12 pf
12 or 120

0.0012uF (1200pf)
122 

0.12 uF
124 
15 pf
15 or 150

0.0015uF
152 

0.15 uf
154 
18 pf
18 or 180

0.0018 uF (1800pf)
182 

0.18 uF
184 
22 pf
22 or 220

0.0022uF
222 

0.22 uF
224 
27 pf
27 or 270

0.0027uF
272 

0.27 uF
274 
33 pf
33 or 330

0.0033 uF
332 

0.33 uF
334 
39 pf
39 or 390
0.0039uF
392 
0.39 uF
394 
47 pf
47 or 470

0.0047uF
472 

0.47 uF
474 
58 pf
58 or 580

0.0056uF
562 

0.56 uF
564 
68 pf
68 or 680

0.0068uF
682 

0.68 uF
684 
82 pf
82 or 820
0.0082uF
822 
0.82 uF
824 
100 pf
101 

0.01 uF
103 

1uF
105 or 1uf
120 pf
121 

0.012 uF
123 

150 pf
151 

0.015 uF
153 



180 pf
181 

0.018 uF
183 



220 pf
221 

0.022 uF
223 



270 pf
271 

0.027 uF
273 



330 pf
331 

0.033 uF
333 



390 pf
391 

0.039 uF
393 



470 pf
471 

0.047 uF
473 



560 pf
561 

0.056 uF
563 



680 pf
681 

0.068 uF
683 



820 pf
821 
0.082 uF
823 

Another good source of charts: http://www.csgnetwork.com/capcodeinfo.html

This article is an introduction to how capacitors work. This is a post in a series I am writing titled 'Introduction to Basic Electronics'. In these posts you fill find necessary tool for using electronic components like capacitors.

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