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How to Determine What Kind of Capacitor You Need

Almost every kind of electronic circuit uses capacitors, and many circuits have several of them. The capacitor's job is to store electrical charges. In doing this, it acts as a charge reservoir and, as it takes time to fill and empty it, it frequently serves as a timing element. Electronics manufacturers make many kinds of capacitors covering a wide range of capacitance values and other electrical and physical characteristics. To determine the kind of capacitor you need, have a schematic handy for the circuit you plan to build.

Things You'll Need

Electronic circuit schematic
Calculator
Electronics component distributor catalog

Instructions

- 1
  Find the capacitor you wish to evaluate on the schematic. The schematic symbol for capacitors is a pair of short parallel lines with a thin blank space between. For a polarized capacitor, one of those lines may be curved and one side will have a polarity mark, such as the + symbol. Note the part's value, which will be stated in picofarads (pF), nanofarads (nF) or microfarads (mF or uF).
- 2
  Note the voltage rating for the capacitor on the schematic. If it has none, calculate it by first determining the voltage present at the capacitor's location. If this is difficult, use the circuit's supply voltage. For example, if the circuit runs on a 9 volt battery, use 9 volts. Enter this number into the calculator, multiply by 1.3 and press the equals key. Round up to the nearest 5 volts. Use the result as the capacitor's voltage rating. For example, if the circuit voltage is 9 volts, 9 x 1.3 equals 11.7. Rounding up gives 15 volts.
- 3
  Refer to an electronics component distributor catalog. Turn to the section on capacitors. For a component having a value of less than 1 nanofarad, see the sections on ceramic or silver mica capacitors. For those with values between 1 nanofarad and 10 microfarads, browse the polyester (Mylar), polystyrene or Teflon capacitors. Capacitors having values of more than 10 microfarads will typically be in the sections for tantalum and aluminum electrolytic types. Find a capacitor with the capacitance value specified in the schematic and use the voltage you calculated or obtained from the schematic.

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