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Capacitors have a variety of marking codes on them. These markings and codes indicate various properties for the capacitors and it is essential to understand them in order to select the required type.
Today most capacitors are marked with alphanumeric codes but older capacitors may be seen that have colour codes. These capacitor colour codes are less common than in previous years, but some may still be seen.
The capacitor marking codes vary in their format according to whether the component is a surface mount device or whether it is leaded device, as well as the capacitor dielectric. Size also plays a major part in determining how the capacitor is marked – small components must use abbreviated coding systems, whereas larger capacitors such as aluminium electrolytic varieties may write the relevant parameters on the case in full.
Some of the marking systems have been standardised by the EIA - the Electronic Industry Alliance, and these provide commonality across the industry.
Capacitor marking codes: the basics
Capacitors are marked in many different ways. There are a number of basic marking systems that are used and different capacitor types and different manufacturers use these as needed and best fits the particular product.
Note: that on some occasions the abbreviation MFD is used to denote µF and not a MegaFarad.
Some of the basic coding schemes for the different parameters are included below:
- Non-coded markings: The most obvious way of marking a capacitor parameters are to directly mark them onto the case or encapsulation in some way. This method works best on larger capacitors where there is sufficient space for the markings.
- Abbreviated capacitor marking codes: Smaller capacitors may only have room for a few figures printed as a code for the value. This capacitor marking code uses three characters. It bears many similarities to the numeric code system adopted for some surface mount resistors. The first two figures refer to the significant figures of the capacitor value, and the third one acts as a multiplier. The value of the capacitor is denoted in picofarads for ceramic, film, and tantalum capacitors, but for aluminium electrolytic capacitors the value is denoted in microfarads.
Multiplier used on EIA Capacitor Marking Code Third Figure Multiplier 0 1 1 10 2 100 3 1000 4 10 000 5 100 000 6 1 000 000
This scheme is widely used with surface mount capacitors where space is very limited.
- Colour code: Some older capacitors use a form of colour code. This type of capacitor marking is used less these days but may be seen on some older capacitors.
- Tolerance codes: Some capacitors have a tolerance code. The code used is actually the same as that used with resistors as it utilises the EIA scheme:
EIA Tolerance Capacitor Marking Code Letter code Tolerance Z +80%, -20% - this is used with electrolytic capacitors where the minimum value is the major issue. M ±20% K ±10% J ±5% G ±2% F ±1% D ±0.5% C ±0.25% B ±0.1%
- Capacitor working voltage codes: The working voltage for a capacitor is very important and therefore this parameter is often marked on capacitors and particularly in situations where there is space for alphanumeric coding. In many instances where the capacitor is small no voltage coding is provided and care must be taken when using a capacitor without any knowledge of its working voltage. Again the marking code uses the EIA scheme:
EIA Capacitor Voltage Codes 0G = 4.0VDC 1J = 63VDC 2D = 200VDC * 0L = 5.5VDC 0k = 80VDC 2P = 220VDC 0J= 6.3VDC * 2A = 100VDC * 2E = 250VDC * 1A = 10VDC * 2Q = 110VDC 2F = 315VDC 1C = 16VDC * 2B = 125VDC 2V = 350VDC 1E = 25VDC * 2C = 160VDC 2G + 400VDC * 1H = 50VDC * 2Z = 180VDC 2W = 240VDC * These codes are preferred values SMD Electrolytic Capacitor Voltage Codes Letter Voltage e 2.5 G 4 J 6.3 A 10 C 16 D 20 E 25 V 35 H 50
Temperature coefficient codes
It is often necessary to mark a capacitor with a marking or code that indicates the temperature coefficient of the capacitor. These capacitor codes are standardised by EIA, but also some other generally used industry codes may also be seen in common use. These codes are typically used for ceramic and other film type capacitors.
The temperature coefficient is quoted in terms of parts per million per degree C; PPM/°C.
|Common temperature coefficient markings|
|EIA||Industry||Temperature coefficient (ppm/°C)|
Capacitor polarity markings
One important marking for polarised capacitors is the polarity. Great care must be taken to ensure the polarity markings are observed when inserting these capacitors into circuits otherwise damage to the component, and more importantly to the remainder of the circuit board can result. Polarised capacitors effectively mean aluminium electrolytic and tantalum types.
Many recent capacitors are marked with the actual + and - signs and this makes it easy to determine the polarity of the capacitor.
Another format for electrolytic capacitor polarity markings is to use a stripe on the component. On an electrolytic capacitor the stripe indicates the negative lead.
If the capacitor is an axial version having leads at both ends of the package, the polarity marking stripe may be accompanied by an arrow that points to the negative lead.
For leaded tantalum capacitors the polarity markings indicate the positive lead. A "+" sign is placed close to the positive lead. When new, a further polarity making may be used because it may be seen that the positive lead is longer than the negative one.
Markings for different types of capacitor
Many larger capacitors like electrolytic capacitors, disc ceramics, and many film capacitors are large enough to have their markings printed on the case.
On a larger capacitors there is sufficient space to mark the value, the tolerance, working voltage, and often other data such as the ripple voltage.
There are a number of subtle differences in the capacitor codes and markings used for different types of leaded capacitors:
- Electrolytic capacitor markings: Many leaded capacitors are quite large, although some are smaller. As such it is often possible to provide the complete value and details in a non-abbreviated format. However many smaller electrolytic capacitors need to have coded markings on them as there is insufficient space.
A typical marking may fall into the format 22µF 50V. The value and working voltage is obvious. The polarity is marked by a bar to indicate the negative terminal.
- Leaded tantalum capacitor markings: Leaded tantalum capacitors generally have their values marked in microfarads, µF.
Typically the markings on a capacitor may give the figures like 22 and 6V. This indicates a 22µF capacitor with a maximum voltage of 6V.
- Ceramic capacitor markings: Ceramic capacitors are generally smaller than types like electrolytic capacitors and therefore the markings need to be more concise. A variety of schemes may be used. Often the value may be given in picofarads. Sometimes figures such as 10n will be seen and this indicates a 10nF capacitor. Similarly n51 indicates a 0.51nF, or 510 pF capacitor, etc . .
- SMD ceramic capacitor codes: Surface mount capacitors are often very small and do not have the space for markings. During manufacture the capacitors are loaded into a pick and place machine and there is no need for any markings.
- SMD tantalum capacitor markings: The most straightforward marking system for SMD tantalum capacitors is where the value is shown directly.On the occasions that there is space for a marking or code, the simple three figure format like that shown below is often used, especially for capacitors such as ceramic formats. For the example of the capacitor code shown in the diagram, the two figures 47 indicate the significant figures and the 5 indicates the multiplier of 5, i.e. 100 000, i.e. 4.7µF.In some cases the only marking shown on the capacitor may be a bar across one end indicating the polarity. This is particularly important because it is necessary to be able to check the polarity and to have a marking to identify the polarity of the capacitor. It is particularly important to have a capacitor polarity marking because reverse biasing tantalum capacitors leads to their destruction.
In general it is very easy to determine what the different capacitor codes and marking schemes mean. Although there appear to be many different coding schemes, they are normally very obvious, and if not their meaning is soon revealed when referring to a coding guide.