Understanding Capacitor Markings

Capacitors are routinely marked with at least their capacitance value; many capacitors are also marked with value tolerance notation, and a breakdown voltage. Additionally, capacitors that are polarized—they have a + and a – lead—also carry a polarization marking.

Capacitance Value

The capacitance values for some capacitors are printed directly on the component. This is true of larger capacitors with values of 1 μF or higher, if for no other reason that their larger physical size allows the manufacturer to directly print the value on the component.

But for other capacitors things aren’t always so simple. Smaller capacitors, such as 0.1 or 0.01 μF disc variety, use a common three-digit marking system to denote capacitance and tolerance. The numbering system is easy to use, if you remember it’s based on picofarads, not microfarads.

A number such as 104 means 10, followed by four zeros, as in

100,000

or 100,000 picofarads. To make the conversion, move the decimal point to the left six spaces: 100000 becomes .1. Note that values under 1000 picofarads do not use this numbering system. Instead, the actual value, in picofarads, is listed, such as 10 (for 10 pF).

Like resistors, the tolerance of the capacitor indicates how close the printed value meets reality. With smaller disc-type capacitors tolerance is most often indicated by a single letter code, which is sometimes placed by itself on the body of the capacitor or after the three-digit mark, such as

104Z

The letter Z donates a tolerance of +80 percent and –20 percent. That means the capacitor, which is rated at .1 μF, might be as much as 80 percent higher or 20 percent lower. See below for a list of letter-style tolerance codes.

RoboTip!
If no tolerance is indicated it’s usually best to assume worst case, which is “Z” (+80%, –20%).

More and more capacitor manufacturers are adopting the EIA (Electronic Industries Association) marking system for temperature tolerance. This mark uses three characters to indicate the temperate tolerance, and maximum variation within the stated temperature range. A table of EIA tolerance markings is shown later in this app note.

For example, a capacitor marked Y5P has the following characteristics:

  • –30°C low temperature requirement
  • +85°C high temperature requirement
  • +/–10.0 percent variance in capacitance over the -30 to +85°C range

Table 1 provides a quick glance at how several common capacitor number markings convert to their μF microfarad equivalents.

Table 1.  Capacitor value reference.

Marking

Value (μF)

 

Marking

Value (μF)

xx (number from 01 to 99)

xx pF

 

 

 

101

0.0001

 

331

0.00033

102

0.001

 

332

0.0033

103

0.01

 

333

0.033

104

0.1

 

334

0.33

221

0.00022

 

471

0.00047

222

0.0022

 

472

0.0047

223

0.022

 

473

0.047

224

0.22

 

474

0.47

Dielectric Breakdown Voltage Value

The dielectric breakdown voltage is only specified for certain capacitors. For those that have it, the voltage is marked directly, such as “35” or “35V.” Sometimes, the letters WV are used after the voltage rating. This indicates the working voltage (really the maximum dielectric breakdown voltage) of the capacitor. You should not use the capacitor with voltages that exceed this value.

On capacitors without a breakdown voltage printed on them you must estimate the value based on the type of dielectric it uses. This is an advanced topic and not covered in this book, and nevertheless, seldom comes up in electronics for robotics because most circuits use 12 volts or less. Only a few capacitors are designed with breakdown voltages less than this, and these are primarily used for such tasks as temporary battery backups.

Polarization Marking

Some capacitors are polarized, that is, they have a + and – terminal. Marking on the capacitor indicates the + or the – terminal.

If a capacitor is polarized, it is extremely important that you follow the proper orientation when you install the capacitor in the circuit. If you reverse the leads to the capacitor—connecting the + side to the ground rail, for example—the capacitor may be ruined. Other components in the circuit could also be damaged.

RoboTip!
By convention, the polarizing mark on aluminum electrolytic capacitors is typically the – (negative) lead. The polarizing mark on tantalum electrolytic capacitors is typically the + (positive) lead.

Capacitor Tolerance Markings

In addition to the capacitance value (and possibly the working voltage or breakdown voltage) the capacitor may be marked by its tolerance.

There are several tolerance marking systems used; two of the most common are shown here. The first is used with small ceramic capacitors, and appears as a single letter.

The second is used for a variety of capacitor types, and is indicated by a unique assortment of lettrs and numbers, which represent the low and high temperature requirements (the lower and upper acceptable temperature range of operating the capacitor), and its tolerance within this temperature range.

Ceramic Capacitor Tolerance Markings

Code

Tolerance

 

Code

Tolerance

B

± 0.1 pF

 

J

± 5%

C

± 0.25 pF

 

K

± 10%

D

± 0.5 pF

 

M

± 20%

F

± 1%

 

Z

+ 80%, -20%

G

± 2%

 

 

 

EIA Capacitor Tolerance Markings

1st Letter Symbol

Low Temp. Requirement

 

Number Symbol

High Temp. Requirement

 

2nd Letter Symbol

Max. Capacitance Change Over Temperature Rating

Z

+10° C

 

2

+45° C

 

A

±1.0%

Y

-30° C

 

4

+65° C

 

B

±1.5%

X

-55° C

 

5

+85° C

 

C

±2.2%

 

 

 

6

+105° C

 

D

±3.3%

 

 

 

7

+125° C

 

E

±4.7%

 

 

 

 

 

 

F

±7.5%

 

 

 

 

 

 

P

±10.0%

 

 

 

 

 

 

R

±15.0%

 

 

 

 

 

 

S

±22.0%

 

 

 

 

 

 

T

±22% ~ 33%

 

 

 

 

 

 

U

±22% ~ 56%

 

 

 

 

 

 

V

±22% ~ 82%

Example:  Y5P = ± 10% variation of temperature over range of -30° C to +85° C.