Contrary to what happens with resistors, capacitors have a wide variety of codes that describe their characteristics. Very small capacitors are particularly difficult to read, due to the limited space for printing. The information in this article should help you recognize the specifications of almost any modern retail capacitor. Don't be surprised if the part numbers on your model are printed in a different order than described here, or if the voltage and tolerance values are not shown. For many low voltage DIY circuits, the only information you need to know is the capacity.
Steps
Method 1 of 2: Large Capacity Capacitors
Step 1. Know the units of measure
The basic unit of measure for capacitance is farad (F). This value is very large for ordinary circuits, so the capacitors you can find in the house have one of the following units:
- 1 µF, uF, or mF = 1 microfarad = 10-6 farad. Be careful; in other contexts, mF is the official abbreviation for millifarad (10-3 Farad).
- 1 nF = 1 nanofarad = 10-9 farad.
- 1 pF, mmF, or uuF = 1 picofarad = 1 micromicrofarad = 10-12 farad.
Step 2. Read the capacitance values
Almost all large capacitors have a capacitance value marked on the side. There are many variations to this rule, so look for the value expressed in the units described above. Consider the following variants:
- Ignore capital letters of the unit of measure. For example, "MF" is simply a variant of "mf". It is certainly not a megafarad, even if that is the official abbreviation SI.
- Don't get confused by "fd". It is simply an abbreviation for farad. For example, "mmfd" is equivalent to "mmf".
- Beware of single letter codes, such as "475m", which you can usually find on smaller capacitors. Read below for instructions on how to interpret them.
Step 3. Look for the tolerance value
On some capacitors the tolerance is indicated, that is the maximum range of capacitance with respect to the nominal value of the device. This is not an important parameter for all circuits, but if you need an exact value, you should be careful. For example, a 50 µF capacitor with a tolerance of ± 5% means that its nominal value is between 5, 25 and 4, 75 µF.
If you don't find any percentage on the capacitor, look for a single letter after the capacitance value or on a separate line. This could be a code to indicate the tolerance value, described below
Step 4. Check the voltage
If there is room on the capacitor, the manufacturer often writes the voltage, as a number followed by V, VDC, VDCW or WV (which stands for working voltage). The value is the maximum potential difference that the capacitor can withstand.
- 1 kV = 1,000 volts.
- Read below if you suspect that the voltage on your capacitor is expressed as a code (a letter or a digit and a letter). If there is no symbol, use the capacitor only in low voltage circuits.
- If you want to build an alternating current circuit, look for a capacitor suitable for this specific type of situation. Do not use capacitors designed for direct current operation unless you are experienced in making the proper circuitry for conversion.
Step 5. Identify the polarity
If you notice + or - symbols next to a terminal, the capacitor is polarized. Make sure you connect the positive terminal to the positive of the circuit, or the capacitor could cause a short circuit, or even explode. If there are no + or - symbols, the orientation of the component does not matter.
Some capacitors use colored bars or a circle cut into the device to signal polarity. Usually, these symbols indicate the negative pole of an aluminum electrolytic capacitor (which is shaped like a can). On tantalum electrolytic capacitors (which are very small), they indicate the positive pole. Do not consider the bars if they contradict the + or - sign or if they are on a non-electrolytic capacitor
Method 2 of 2: Interpreting the Capacitor Codes
Step 1. Write the first two digits of the capacity
Older models are not easy to interpret, but almost all modern ones adopt the standard EIA codes when the capacitor is so small that it cannot write the full capacitance value. To get started, write down the first two digits, then find out what to do according to the code shown:
- If the code has exactly two digits followed by a letter (e.g. 44M), the first two digits are the capacity value. Skip to the units section.
- If one of the first two characters is a letter, jump to letter systems.
- If the first three characters are all numbers, continue to the next step.
Step 2. Use the third digit as a decimal multiplier
The three-digit capacity code works as follows:
- If the third digit is a number from 0 to 6, add that number of zeros to the end of the value. For example, 453 → 45 x 103 → 45.000.
- If the third digit is 8, multiply the value by 0.01 - for example: 278 → 27 x 0.01 → 0.27)
- If the third digit is 9, multiply the value by 0, 1 - for example: 309 → 30 x 0, 1 → 3, 0)
Step 3. Find the unit of measure of capacity from the context. The smallest capacitors (made of ceramic, cellulose or tantalum) have capacities in the order of picofarads (pF), which is equivalent to 10-12 farad. The largest capacitors (electrolytic cylindrical aluminum or double layer capacitors) have capacities in the order of microfarads (uF or µF), which is equivalent to 10-6 farad.
Capacitors that do not respect these conventions report a unit of measurement after the capacitance value (p for picofarads, n for nanofarads, u for microfarads). However, if you only see one letter after the code, it usually indicates the tolerance, not the unit of measurement. P and N are little used, but still exist, tolerance codes
Step 4. Read the codes that contain letters. If one of the first two characters of your code is a letter, there are three possibilities:
- If the letter is an R, replace it with a comma to get the capacitance in pF. For example, 4R1 indicates a capacitance value of 4.1 pF.
- If the letter is a p, an n or a u, it indicates the unit of measurement: pico-, nano- or microfarad. Replace it with a comma. For example, n61 is 0.61 nF and 5u2 means 5.2uF.
- A code similar to "1A253" actually contains two pieces of information. 1A indicates the voltage and 253 expresses the capacitance as described above.
Step 5. Read the tolerance code on the ceramic capacitors
Usually, on ceramic capacitors, which are often two tiny round "squeezers" with two connectors, the tolerance value is indicated by a letter directly following the three-digit capacitance value. That letter represents the tolerance of the capacitor, that is the range of values that the real capacity of the device can assume, in relation to the nominal one. If it's important that your circuit is accurate, you can interpret that code as follows:
- B = ± 0.1 pF.
- C = ± 0.25 pF.
- D = ± 0.5 pF for capacitors with capacitance values less than 10 pF, or ± 0.5% for capacitors with capacitance values greater than 10 pF.
- F = ± 1 pF or ± 1% (the same distinction made for D above applies).
- G = ± 2 pF or ± 2% (read above).
- J = ± 5%.
- K = ± 10%.
- M = ± 20%.
- Z = + 80% / -20% (If no tolerance value is listed, assume it is this).
Step 6. Read the tolerance values expressed in letter-number-letter form
On many types of capacitors the tolerance is indicated with a more detailed three symbol system. Interpret it as follows:
- The first symbol indicates the minimum temperature. Z = 10 ° C, Y = -30 ° C, X = -55 ° C.
-
The second symbol shows the maximum temperature.
Step 2. = 45 ° C
Step 4. = 65 ° C
Step 5. = 85 ° C
Step 6. = 105 ° C
Step 7. = 125 ° C.
- The third symbol shows the change in capacity over the temperature range. It goes from TO = ± 1.0%, the most accurate, a V. = +22.0% / - 82%, the least accurate. R., one of the most common symbols, represents a variation of ± 15%.
Step 7. Interpret the codes that indicate the voltage. You can consult the EIA voltage table if you want a complete list, but almost all capacitors use one of the following codes to express the maximum potential difference (values referring only to direct current capacitors) to which they can be subjected:
- 0J = 6.3V
- 1A = 10 V
- 1C = 16 V
- 1E = 25 V
- 1H = 50 V
- 2A = 100 V
- 2D = 200 V
- 2E = 250 V
- One-letter codes are abbreviations of the most common above values. If multiple values (such as 1A or 2A) can be applied, you will need to find the right one from the context.
- To estimate the value indicated by other less common codes, look at the first digit. 0 stands for values below 10; 1 goes from 10 to 99; 2 goes from 100 to 999 and so on.
Step 8. Study other systems
Old capacitors or those made for special uses adopt different classification systems. They are not included in this article, but you can use these tips to conduct more in-depth research:
- If the capacitor has a single long code that begins with "CM" or "DM," do some research on the capacitor tables used by the US military.
- If you don't notice a code, but there is a series of bands or colored dots, look for the color codes of the capacitors.
Advice
- The capacitor can also report operating voltage information. The device should withstand a greater potential difference than the operating circuit in which you wish to use it.
- 1,000,000 picoFarad (pF) equals 1 microFarad (µF). Many common capacitors have capacities close to these values, which can be reported in either unit of measurement. For example, a 10,000 pF capacitor is most often considered a 0.01 uF device.
