Last Updated on October 22, 2023 by Kevin Chen
Compared to other capacitors, an electrolytic capacitor has one of the greatest capacitances. The electrolytic capacitor is just one type of capacitor in use today. This article explains electrolytic capacitors and how they work.
What Is Electrolytic Capacitor
Electrolytic capacitors are typically utilized when a large charge must be stored in a compact space. The liquid electrolyte serves as one of the electrodes in electrolytic capacitors (mostly act as the cathode). To comprehend the concept of an electrolytic capacitor, we must first comprehend the operation of a basic capacitor.
What Is A Capacitor
An electronic device that stores electric charge is known as a capacitor. It comprises two conductive plates separated by a dielectric insulating substance. Depending on the application, different insulating materials are employed to form the dielectric.
The capacitor’s conducting plates are excellent electrical conductors. As a result, electric current can easily pass through them. A dielectric medium or material, on the other hand, is a poor conductor of electricity. As a result, electric current cannot pass through it.
The capacitor begins to charge when electricity is provided to it so that the negative terminal of the battery is linked to the right-side plate and the positive terminal of the battery is connected to the left side plate.
The electrons begin to flow from the battery’s negative terminal to the right-side plate due to this supply voltage. Because dielectric material is a poor conductor of electricity, the electrons face severe opposition once they reach the right-side plate.
As a result, the right-side plate capacitor traps many electrons. The huge quantity of electrons, on the other hand, exerts a force or electric field towards the left side plate. As a result, electrons on the left side plate are repelled by extra electrons on the right-side plate. As a result, electrons are drawn to the battery’s positive terminal and travel away from the left side plate.
As a result of the extra electrons, the right-side plate gets more negatively charged (negative charge builds). On the other hand, the left side plate becomes increasingly positively charged (positive charge is built) when electrons are lost. Voltage is established between the plates as a result. This is how a standard capacitor functions.
Similarly, the electrolytic capacitor charges in a similar manner, On the other hand, the electrolytic capacitor is made of a different substance.
What Is an Electrolyte?
Electric current is conveyed by moving ions in an electrolyte, a liquid electric conductor. Electrolytes or minerals, for example, carry a charge in our blood. Salt, potassium, chloride, calcium, and phosphorus are the most common electrolytes.
Anions (-) and cations (+) are the two types of ions found in electrolytes. An anion is an ion with more electrons than protons. Electrons have a negative charge, while protons have a positive charge. The total charge of the atom or anion becomes negative due to the excess number of electrons over protons. As a result, anions are referred to as negatively charged ions. Negatively charged anions are those that have a negative charge.
In contrast to protons, cations have fewer electrons. Because there are fewer electrons than protons, the atom or cation’s total charge becomes positive. As a result, cations are referred to as positively charged ions. These positively charged cations carry a positive charge.
Types of Electrolytic Capacitors
Electrolytic capacitors are classified into three types based on the material used to construct the dielectric:
- Aluminum electrolytic capacitors
- Tantalum electrolytic capacitors
- Niobium electrolytic capacitors
In this tutorial, an aluminum electrolytic capacitor is explained. The aluminum, tantalum, and niobium electrolytic capacitors work similarly. The substance utilized to make electrodes, on the other hand, is different.
Aluminum Electrolytic Capacitor
Two aluminum foils, an aluminum oxide layer, an electrolytic paper or paper spacer soaked in electrolytic liquid or solutions, and liquid or solid electrolyte make up an aluminum electrolytic capacitor. The electrolytic liquid comprises atoms or molecules that have received or lost electrons.
The anode (+) and cathode (-) of an aluminum electrolytic capacitor are made of pure aluminum foil. A thin layer of insulating aluminum oxide is applied to the anode aluminum foil (aluminum element with oxygen element). The electrolytic capacitor’s dielectric, which prevents electric current passage, comprises this insulating aluminum foil. An electrolytic paper separates the cathode and the oxide-coated anode (soaked in an electrolytic liquid).
The cathode aluminum foil is also protected by a very thin insulating oxide layer or dielectric, generated naturally by air. However, compared to the oxide layer generated on the anode, this oxide layer is quite thin.
As a result, the aluminum electrolytic capacitor seems to be composed of two capacitors connected in series with anode capacitance CA and cathode capacitance CK.
The formula for the serial connection of two capacitors yields the total Capacitance of the capacitor:
Where CA = Capacitance of anode
CK = Capacitance of cathode
Cecap = Total Capacitance of an electrolytic capacitor
We know that the Capacitance, or charge storage capacity, is related to the surface area of the conducting plates or electrodes and inversely proportional to the dielectric thickness. In other words, capacitors with large electrodes store a lot of charges, whereas capacitors with small electrodes only store a little. Capacitors with a very thick dielectric store a small amount of charge, whereas capacitors with a very thin dielectric store a huge charge.
The dielectric in conventional capacitors is thick, resulting in low Capacitance per volume. The electrolyte serves as a genuine cathode in electrolytic capacitors, with a huge surface area and a thin dielectric. Electrolytic capacitors can store a considerable quantity of charge due to the enormous surface area of the electrode and the thin dielectric.
The electrolytic capacitor’s electrical conductivity rises as the temperature rises and falls as the temperature falls. As a result, the aluminum electrolytic capacitor’s capacitance (or charge storage) increases with increasing temperature and decreases with decreasing temperature. As a result, temperature changes significantly impact the Capacitance of the aluminum electrolytic capacitor.
The majority of electrolytic capacitors are polarized, which means that the voltage applied to the terminals must be in the proper polarity (positive connected to the positive terminal and negative connected to the negative terminal). Suppose it is connected in the wrong direction or reverse. The capacitor may be short-circuited, which causes a high electric current to flow through it, permanently damaging the capacitor.
A minus sign (-) or a plus sign (+) is indicated on one of the two leads of polarized capacitors. This polarity has to be adhered to.
What Characteristics does an Electrolytic Capacitor have?
Capacitance Drift
Electrolytic capacitors have large tolerances, sometimes as much as 20%, and their capacitance changes with time from the nominal amount. A 47f nominal capacitance aluminum electrolytic capacitor should have a measured capacitance of 37.6f to 56.4f. Tantalum electrolytic capacitors have tighter tolerances but a lower maximum working voltage; therefore, they aren’t usually a direct substitute.
Polarity and Safety
Because of their construction and the properties of the electrolyte used, electrolytic capacitors must be forward biased. As a result, the voltage at the positive terminal must always be greater than that at the negative terminal. The insulating aluminum oxide, which functions as a dielectric, could be destroyed if the capacitor is reverse-biased (the voltage polarity on the terminals is reversed). This could result in a short circuit between the two capacitor terminals.
Because of the high current flowing through the capacitor, it may overheat. The electrolyte warms up and spills or vaporizes as the capacitor overheats, causing the enclosure to explode. At reversal voltages of around 1 volt and above, this process occurs. A safety valve is inserted to preserve the safety and prevent the enclosure from exploding due to high pressures created under overheating circumstances.
It’s usually constructed by scoring the capacitor’s upper face, which then explodes open in a controlled manner when the capacitor overheats. Because electrolytes can be poisonous or corrosive, extra caution should be exercised when cleaning and replacing an overheated electrolytic capacitor. There is a specific type of electrolytic capacitor for AC application that can survive reverse polarization. Non-polarized, or NP, is the name given to this type.
Construction and Properties of Electrolytic Capacitors
Metal electrolytic capacitors are two aluminum foils and a soaked-in-electrolyte paper spacer. One of the two aluminum foils has an oxide layer and serves as an anode, while the other serves as a cathode. The anode must be at a positive voltage in proportion to the cathode during normal operation, which is why the cathode is usually marked with a minus sign throughout the capacitor’s body.
The cathode, anode, and electrolyte-soaked paper are all packed together. The stack is rolled and placed in a cylindrical casing, and pins are used to link it to the circuit. Axial and radial geometries are the most prevalent. One pin is situated on each end of the cylinder in axial capacitors, whereas in radial capacitors, both pins are located on the same end.
Electrolytic capacitors, which range from 1F to 47mF in Capacitance, have a higher capacitance than most other capacitor types. A double-layer capacitor, sometimes known as a supercapacitor, is a unique type of electrolytic capacitor with a capacitance of thousands of farads. Several parameters, such as plate area and electrolyte thickness, influence the Capacitance of an aluminum electrolytic capacitor. A big capacitance capacitor is bulky and enormous as a result of this.
It’s worth noting that electrolytic capacitors manufactured with older technologies had a short shelf life, usually only a few months. The oxide layer deteriorates with time if the capacitor is not utilized, and it must be repaired in a process known as capacitor reformation. This can be accomplished by attaching the capacitor to a voltage source via a resistor and gradually raising the voltage until the oxide layer has been rebuilt completely. Modern electrolytic capacitors have a two-year or longer shelf life. The capacitor must be reformed before use if left unpolarized for an extended time.
An Electrolytic Capacitor’s Functions and Principles of Operation
Electrolytic capacitors have polarized components because they are designed asymmetrically. The greater voltage operation of this arrangement explains why one side receives more power than the other. The capacitor’s positive electrode is a metal or aluminum anode with an oxidized cover layer that functions as a dielectric and operates as a dielectric. The majority of the input voltage is directed to this site.
The negative electrode is the cathode, made up of aluminum foil and a liquid electrolyte. Water and sodium borate or boric acid are the most common ingredients in this liquid. To prevent evaporation, a few sugars are added. The polarity of electrolytic capacitors is determined by aluminum oxide. The electric field keeps it in place.
The correct polarity must be present when applying direct current (DC) voltage to an electrolytic capacitor. The positive lead and positive terminal and the negative lead and negative terminal must be connected for this to work. The capacitor will be damaged if this is not done properly.
What Are the Applications Of An Electrolytic Capacitor?
The following are some applications for electrolytic capacitors:
An electrolytic capacitor can be utilized in several filtering applications to reduce the amount of voltage ripple. In audio amplification circuits, this is done to reduce hums.
When the signal is a DC signal with a faint AC component, an electrolytic capacitor can be used as a low pass filter in the input and output smoothing. On the other hand, Electrolytic capacitors struggle with large amplitude and high-frequency signals due to the power wasted at the parasitic internal resistance known as equivalent series resistance (ESR). To minimize losses and avoid overheating, low-ESR capacitors must be utilized in these applications.
A polarity effect and overheating can occur in an electrolytic capacitor. With high-frequency broadcasts, this does not operate well. It is influenced by the resistance it contains. This form of resistance is known as equivalent series resistance. Power dissipation is the primary source of this.
Does an Electrolytic capacitor have any Disadvantages?
There are some drawbacks to using an electrolytic capacitor. The benefit of high Capacitance in an electrolytic capacitor comes with a slew of drawbacks, including value tolerances, equivalent series resistance, and a short lifetime.
It could also fail to perform its role, causing leakage and bulkiness. Because most electrical devices have a low Equivalent Series Resistance (ESR) when using an electrolytic capacitor, a high ESR is one failure mode. However, the failure could be caused by the capacitor failing to open, implying that the electric flow is not adequately distributed among the circuits.
Conclusion
We may deduce from the post that practically all electrolytic capacitors are polarized, implying that the positive terminal voltage must always be greater than the negative terminal voltage. With increased surface area and decreasing distance between anode and cathode, a component’s Capacitance rises. An electrolytic capacitor uses a solid, liquid, or gel electrolyte as the cathode or negative plate to provide a much higher capacitance per unit volume.
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