Electrolytic Capacitor – Symbol, Types, Construction & Uses

An electrolytic capacitor is a polarized capacitor that utilizes an electrolyte to achieve a larger capacitance than other types of capacitors. Electrolytic capacitors are often used when high charge storage is required in a small volume. In this article, we will discuss the classification, construction, and uses of electrolytic capacitors.

An electrolytic capacitor
An electrolytic capacitor

What is an electrolyte inside the Electrolytic Capacitor?

An electrolyte is a liquid or gel that acts as an electrical conductor and has a significant amount of current-carrying ions in it.

In electrolytes, ions can either be cations (+) or anions (-). The proton has a positive charge, whereas the electron has a negative charge. When an ion has more electrons than protons, it is referred to as an anion. Therefore anion is negative. On the other hand, cation has a positive charge because there are fewer electrons than protons in it.

When a voltage is applied across the electrodes of the capacitor, the ions in the electrolyte flow from one electrode to the other, creating an electric current. This current creates an electrostatic field that stores energy in the form of an electrostatic charge. The amount of charge that can be stored in an electrolytic capacitor is determined by the size of the electrodes and the type of electrolyte used.

Note: At temperatures of up to 85°C, medium to high voltage electrolytic capacitors use ethylene glycol (EG) or boric acid as the electrolytes.

Symbol of an electrolytic capacitor

The symbol of an electrolytic capacitor is shown in the figure below. One straight line and one curved line, or two parallel straight lines, are used to denote an electrolytic capacitor. To indicate whether a drawn line is a positive or negative terminal, a plus or minus sign is written close to that line (anode or cathode).

Symbol of electrolytic capacitor
Symbol of electrolytic capacitor

Electrolytic capacitors with non-solid electrolyte have a polarity marking on the cathode (minus) side, with a shorter lead, while the electrolytic capacitors with solid electrolyte have a polarity marking on the anode (plus) side, except for cylindrical led (single-ended) and SMD polymer capacitor.

Note: Applying as little as 1 to 1.5 volts in reverse polarity may damage the capacitor.

What are the types of Electrolytic Capacitors?

Electrolytic capacitors
Electrolytic capacitors

Electrolytic capacitors may be categorized based on the various metal types and shapes of the anode valve, the voltage level, the packaging type or electrolyte forms, the use of the capacitor, and the working environment. The list below shows all types of electrolytic capacitors.

Based on anode valve metal:

  • Aluminum electrolytic capacitor
  • Tantalum electrolytic capacitor
  • Niobium electrolytic capacitor

Based on the shape of the anode metal:

  • Foil electrolytic capacitors.
  • Sintered electrolytic capacitors.
  • Tantalum wire electrolytic capacitors
  • Aluminum sheet electrolytic capacitors

Based on electrolyte form:

  • Liquid electrolytic capacitor
  • Dry electrolytic capacitor
  • Solid electrolytic capacitor
  • Non-solid electrolytic capacitor

Based on the capacitor shape package:

  • Fully sealed electrolytic capacitors
  • Non-sealed or semi-sealed electrolytic capacitors.

Based on working voltage:

  • Ultra-low-voltage capacitors,
  • Low-voltage capacitors,
  • Medium-voltage capacitors,
  • High-voltage capacitors
  • Ultra-high-voltage capacitors

Based on polarity:

  • Bullhorn or bolt-type capacitors
  • Bipolar electrolytic capacitor

Based on working environment and usage:

  • Normal temperature (-40℃~+85℃) capacitors,
  • High temperature (above 105℃) capacitors,
  • Wide temperature (-55℃~+125℃) capacitors

Other capacitors:

  • DC capacitors,
  • High-ripple capacitors,
  • AC (such as single-phase motor start) capacitors
  • High-voltage energy storage capacitors,
  • Low-frequency power amplifier capacitors,
  • Camera flash capacitors,
  • Laser energy capacitors.
  • Electromagnetic ejection capacitors
  • Electromagnetic railgun capacitors

Read also: 25 Types of Capacitors & their Uses (Explained in detail)

How is an electrolytic capacitor constructed?

Construction of an electrolytic capacitor
Construction of an electrolytic capacitor

Electrolytic capacitors consist of a cathode, anode, dielectric layer, and an electrolyte. The anode is made of metal. Common metals used for the anode are Aluminium, tantalum, and niobium. Dielectric material needed for the capacitor is produced from the anode metal itself through the process of anodization. So formed dielectrics are aluminum oxides, tantalum pentoxide, and niobium pentoxide respectively.

The electrolyte of the capacitor can be solid, liquid or gel. This electrolyte covers the oxide layer and acts as a cathode of the capacitor. Due to this enlarged anode surface and very thin dielectric oxide layer, electrolytic capacitors can have a high capacitance voltage per unit volume. Hence they can have a high capacitance value. Read more

A close view of the electrolytic capacitor
A close view of the electrolytic capacitor

The capacitance of electrolytic capacitors ranges from 1µF to 47000µF.

Advantages of Electrolytic capacitor

  • Electrolytic capacitors are used to achieve a high capacitance value for a given volume.
  • It is mostly suitable for low-frequency applications.
  • Tantalum-type electrolytic capacitors have higher stability.
  • Electrolytic capacitors possess a very wide tolerance.
  • They are relatively cheaper when compared to other types of capacitors with similar capacitance values.
  • It helps in quick charging and discharging.
  • Minimal maintenance is required for proper functioning.
  • Electrolytic capacitors have self-healing capability.

Self-healing is the ability of a capacitor to recover itself when subjected to some problems during  normal operation

Disadvantages of Electrolytic Capacitors

  • Electrolytic capacitors have high leakage current and wide tolerance which limits their range of applications.
  • It must be ensured that the electrolytic capacitors are connected with proper polarity or else they will explode.
  • Reverse voltage damages the electrolytic capacitor.
  • The performance of electrolytic capacitors may easily get affected due to changes in temperature.
  • It has a limited lifespan.
  • Electrolytic capacitors are not suitable for AC applications.
  • They are not capable of withstanding overvoltages.

Read also: Guide to Ceramic Capacitors- Uses, Types, Characteristics & FAQs

Multiple contacts in a capacitor
Multiple contacts in a capacitor

Applications and Uses of electrolytic capacitor

Electrolytic capacitors are used in the areas where they do not need tight tolerances and AC polarization but require large capacitance values. They are mainly used for:

  • Preventing voltage fluctuations in different filtering devices.
  • Used as an input-output smoothing filter.
  • Used for filtering noise or decoupling in power supplies.
  • Helps in controlling the coupling of signals between amplifier stages.
  • Storing energy in low-power applications or in flashlamps.
  • To provide time delays between two functions in a circuit.
  • Used as filters in audio amplification circuits to reduce hum.

Read also: What is the Difference Between Battery and Capacitor? (Solved)

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