We often field requests for capacitors based on description, such as CAP 0805 4.7UF 5% 25V, CAP TH 1UF 50V 10%, or CAP CER 1PF 0402 1% 6.3V. What do all these obscure-looking numbers mean, and is it possible to find these components without a degree in electronics?
Absolutely you can.
Let’s break down what each of these indicators is, and how you can use it to locate orderable parts.
CAP is simply common shorthand for “Capacitor” and indicates the type of part you’re looking for. You may also see “RES” for resistor, “IND” for Inductor, and so forth, but for now we’ll focus on capacitors. You may also see words like ‘CER’, ‘ALUM’, ‘TANT’, and the like. These indicate the material the capacitor is made of, with the indicated callouts meaning Ceramic, Aluminum (Electrolytic), and Tantalum respectively. This can further help narrow down your search.
0805 is an example of a chip or SMD capacitor size code. These size codes determine the physical size of the part and are most commonly used for either ceramic capacitors - often called MLCC or multi-layer ceramic capacitors - or tantalum parts. Size codes must match - you cannot replace an 0805 part with an 0603 part without redesigning your board. Common size codes include 0201, 0402, 0603, 0805, 1206, 1210, 2012, 2512, and so forth. These size codes will become second nature as you work with these components, but in general any four-digit number without any other sign or unit is a size code.
TH means the part is a through-hole capacitor. Through-hole capacitors are usually either ceramic (old-style disc capacitors) or aluminum electrolytic, and can also be called “Radial” or “axial” parts. Generally, if a through-hole capacitor has high capacitance but low voltage, it’s an aluminum part. If those numbers swing the opposite way, it’s a ceramic part.
1%, 5%, and 10%, and any other number with a “%” sign next to it, are all different values for tolerance. Tolerance is the range from which a capacitor can vary from its listed capacitance value (called its nominal capacitance) and still be considered by the manufacturer to be within its specifications. For example, a 1000pf capacitor (one thousand picofarads) with a ±10% tolerance can vary as far as 10% away from 1000pf. This means a physical example of the part can be anywhere from 900pf to 1100pf and still be considered within spec. Note that tolerance values given without a sign, such as “10%”, are considered to be plus or minus their value. The more precise way to write this is ±10%. Some parts, especially very old ones, will have different values for the plus and minus sides of tolerance, such as +80/-20%. This means the part can vary twenty percent below its nominal value, but as high as eighty percent above. Smaller tolerance values are better - 1% is much tighter and thus a higher quality part than 5% or 10%. All else being equal, you can always use a lower tolerance part in place of an equivalent part with higher tolerance. Consult an engineer familiar with your project if you have to use a higher tolerance part.
25V, 50V, 6.3V, and any other number with a ‘V’ next to it are all examples of voltage rating. Sometimes also called working voltage (WV), this is the maximum steady-state voltage level the capacitor is rated to withstand without damage. A 50V part, for example, can be subjected to 50V continuous voltage and be expected to work just fine. Some capacitors, especially film capacitors, have different ratings for AC voltage (VAC) and DC voltage (VDC). Ensure you’re looking at the correct voltage for your application! Higher voltage is better. A 50V part can withstand the same voltage as a 25V part without any issue, and often experiences longer lifetime to boot. All else being equal, you can use a higher voltage part freely. Do not use a lower voltage part unless you’re certain your circuit has the overhead built in to avoid burning up the capacitor.
4.7uf, 1uf, and 1pf are all examples of capacitance. This is the most important specification for a capacitor and is the reason it gets put on a board. Capacitance can vary wildly depending on the nature of the cap, but most often you’ll see values such as pF, nF, uF (or μF, if your keyboard can produce the Greek symbol ‘mu’), occasionally mF, or sometimes even a F or higher value for supercaps. These are multipliers, or in this case divisors, meaning picofarad, nanofarad, microfarad, millifarad (sometimes), or farad. These can be written in many different ways and there’s a bit of math behind them, but in this case you should simply try to match the value. Some projects might be able to get away with a close-enough value, but if you don’t know if yours is one of them, match the value to the best of your ability.
A note on the ‘MF’ value - this is an unfortunately common “gotcha!” in capacitor sourcing. “MF”, in the case of large motor capacitors and other power electronics, often means microfarads, rather than millifarads as one might expect. In power electronics it’s unfortunately common for the abbreviation to simply be MicroFarad. This is not how the rest of the industry works. Please keep this in mind when searching for motor start, motor run, or other large inductive-load capacitors.
And that’s it! Armed with this knowledge, you should be able to hunt down basic capacitors as needed within DigiKey’s website. As always, if you’re having trouble, feel free to contact DigiKey Applications Engineering for assistance.