When putting together a circuit, it would be nice if discrete components had every spec written right on them. But the fact is, normally there’s just not enough space to display this information in plain English. While any engineer knows that the color markings on a resistor signify the resistance, some may not realize that capacitors also have their own set of markings, which vary depending on the size of the device. This article will explore just what these markings mean on a number of different components.
Simply stated, a capacitor is a device that can store a charge, acting as a sort of short-term battery that can smooth out power fluctuations and perform a variety of other jobs. They range in size from the head of a pin to somewhere in the vicinity of a soda can, so both the characteristics of capacitors and the ability to print information on them vary greatly.
The pertinent specs of a capacitor include:
Capacitance: How much charge the component can store, measured in farads (coulombs per volt)
Breakdown Voltage: The voltage at which the capacitor is no longer able to store a charge, breaking down into a short (or nearly short) circuit
Tolerance: How close to the given capacitance the capacitor can be expected to stay
Polarization: Some (but not all) capacitors have a positive and negative lead. If so, the polarization marking indicates the negative side, and generally takes the form of a lightly colored stripe
Let’s examine some typical capacitor markings.
The image above is of an electrolytic capacitor marked with “100μF,” meaning it has a capacitance of 100 microfarads (the μ prefix indicates 10−6). Expressed differently, this is 0.0001 farads. While this might seem like an extremely tiny number, it’s actually fairly typical, as a full farad is quite large in practical terms.
This particular capacitor is also marked “50 v,” which signifies its breakdown voltage. It indicates that the capacitor breaks down at 50 volts. Finally, the white stripe indicates the negative leg of this capacitor, which is generally also the shorter leg.
The above image shows a Mylar film capacitor. The top “683” marking indicates the capacitance value, which is 68,000 picofarads (pF). To get this value, you multiply the leading digits (68 in this case) by 10 raised to the power of the last digit (3), and the result is the capacitance in picofarads (in this case, we get 68x103 pF). There are three exceptions for the last digit: 7 is not used, 8 means to multiply the leading digits by 0.01, and 9 means to multiply the leading digits by 0.1.
The dielectric breakdown voltage of this capacitor is written underneath the capacitance as “100V,” meaning it breaks down at 100 volts. There is no negative indicator, as this capacitor doesn’t have a dedicated polarity and can be installed either way.
The above image shows a pair of ceramic disk capacitors labeled only as “10” and “15.” These capacitors—and all those under 1000pF—directly show their capacitance in picofarads. Therefore, the capacitance of these two capacitors are 10 and 15 picofarads, respectively. As in the previous case, these capacitors also have no polarity to display. Because of their small size, there’s no markings for the dielectric breakdown voltage—you’ll need to look it up on the capacitor’s spec sheet.
In addition to the above examples, capacitors may also display other specs such as working temperature range, date of manufacture, and even the manufacturer’s name. Capacitors may also indicate their tolerance with a letter placed after the first three numbers. These letters range from A (±0.05pF) to Z (-20 to 80%). The table below gives more of these tolerance codes.