Electrolytic capacitors in short ‘elco’ are capacitors with a fixed, non-adjustable capacitance. Capacitors are able to store energy and release it later.

Electrolytic capacitors are commonly used to store charges or to prevent dips in power supply voltages. Electrolytic capacitors can store bulk energy with capacitance values in the range between 1 μF (micro Farad, 1 μF or 1 uF = 1 * 10-6 F) and 10 mF (milli Farad, 1 mF = 1 * 10-3 F).

All electrolytic capacitors are made of a metal that forms an insulating oxide layer through anodization. This oxide layer acts as the dielectric of the electrolytic capacitor. A non-solid or solid electrolyte covers the surface of this oxide layer, serving in principle as the second electrode. Because of this they are polarized (meaning they have a ‘+’ and ‘-‘ side).

The common aluminium electrolytic capacitors show less ideal behaviour compared to ceramic or film capacitors. They have a leakage current which depends on applied voltage and temperature. This makes them less suitable for applications where this is a problem. Also they tend to deteriorate over time depending on temperature.

In case you need high capacity capacitors with low leakage current and long-term stability, you may decide to use a more expensive tantalum electrolytic capacitor.


Be aware of the polarity of all electrolytic capacitors. Elcos may explode when connected to power incorrectly.


Polarity is usually indicated on the package of the electrolytic capacitor either by:

  • ‘+’ and ‘-‘ signs close to the corresponding terminal
  • for through-hole elcos commonly the ‘-‘ side is indicated by a line sometimes including ‘-‘  signs
  • for surface-mounted elcos commonly the ‘+’ side is indicated by a line

Most important specifications

  • Capacitance (F), usually in the range from μF to mF
  • Maximum voltage DC (V)