Electrostatics

Electrolytic Capacitor

Electrolytic capacitor refers to a type of capacitor that makes use of an electrolyte to facilitate a capacitance that is larger than other capacitor types. Furthermore, almost all electrolytic capacitors are characterized as being polarized. This means that the positive terminal’s voltage should always be greater than the negative terminal’s voltage.

Introduction to Electrolytic Capacitor

An electrolytic capacitor refers to a polarized capacitor that achieves a larger capacitance than other types due to making use of an electrolyte. An electrolyte is simply a fluid or gel having a very high concentration of electrons.

The ability of large capacitance makes an electrolytic capacitor very useful for sending signals of low-frequency. Furthermore, they are useful in power supplies for noise decoupling or filtering. The electrolytic capacitors have a few drawbacks like a limited lifetime, equivalent series resistance, and leakage currents.

electrolytic capacitor

How do we Measure the Electrolytic Capacitor?

There are two main ways of measuring or testing capacitors: through using an LCR meter or via a DVM. Many LCR meters apply a signal’s output source through a source resistor to the range resistor Rr and unknown device ZX.

Furthermore, the amplifier causes the same current, whose flowing takes place through the unknown device, to flow through Rr. Moreover, the unknown device’s junction and Rr is equal to 0 V. The connection of voltages V1 and V2 across the unknown device and across Rr, respectively takes place to a selector switch.

The connection of the switch’s output takes place to a differential amplifier. Furthermore, one can get the imaginary and real components of the current signals and voltage by multiplying these voltages with a square wave coherent that is characterized with the stimulus (in the phase detector). Moreover, this gives an output that is proportional to
the quadrature or in-phase voltage’s component.

The output goes to a dual-slope A/D converter whose reading takes place through the MCU. Furthermore, the complex ratio of voltage to current turns out to be equal to the complex impedance. Moreover, the derivation of the parameters such as L and C takes place mathematically from the corrected impedance value.

There is an application of a sine wave excitation of some selectable frequency to the capacitor by the LCR meter. Afterwards, the measurement of the voltage takes place. Also, this voltage is across the capacitor while the current is through it.

From there, the calculation of the capacitance can take place. Benchtop LCR meters may have certain special settings such as for dc bias voltage or current.

Testing of the electrolytic caps must take place at the frequency that appears in the end application. This is because a variation in capacitance may take place with frequency. Furthermore, some common LCR measurement frequencies are 50/60 Hz, 120 Hz, 1 kHz, 100 kHz and 1 MHz.

One can set the LCR meters to apply different signal levels to the cap under test. Furthermore, this is useful because the testing of electrolytic capacitors must take place at the voltage that is in actual use.

One can use the DVMs to test electrolytic caps if there is no availability of an LCR meter. Some DMs have a capacitance measurements setting. When in the capacitance measurement setting, the measurement of the capacitance takes place by the DVM by using the concept of the RC time constant.

The meter applies a known current via a known resistance to the capacitor. This happens in order to measure how long would it take for the voltage across the capacitor to ramp up. The meter then solves for C due to the time constant relationship.

One must understand that the measurement of the DVM capacitance happens at one frequency. Moreover, this frequency is not necessarily the frequency at which the service of cap takes place. Also, a DVM capacitance measurement does not occur at the relatively high voltages that electrolytic caps would normally encounter.

One can also test electrolytic caps with a DVM that is without a setting for capacitance measurement. Moreover, this procedure figures out capacitance by using the same RC time constant calculation whose use takes place in meters with a setting for capacitance. The difference is that the operator does the calculation manually.

Formula of Capacitance of Electrolytic Capacitor

A capacitor is an electric component that takes place from creating a small gap between layers which carry the charge. The capacitance is the charge collected divided by the voltage difference that exists across the capacitor.

The measurement of capacitance takes place in Farads (F), the measurement of charge takes place in Coulombs (C). Moreover, the measurement of voltage takes place in Volts (V).

Capacitance = electric charge/voltage drop across capacitor

C = Q/V

C = capacitance (Farads, F)

Q = the charge that is built on the capacitor (Coulombs, C)

V = voltage difference that exists between two sides of a capacitor (Volts, V)

Derivation of the Formula of Capacitance of Electrolytic Capacitor

Capacitance refers to the capacity of two conductor plates for the purpose of storing electrical energy between them. Furthermore, the storing of the charge takes place in a given potential difference between the plates.

C = Q/V ⟶ eqn (i)

Now, we know that the expression of E⃗ between the plates of capacitors can take place as:-

⟹ E⃗ = Q/Aϵo ⟶ eqn (ii)

Consider the ΔV between the plates to be V and distance that exists between them to be d,

⟹ V = Ed

One can achieve the above formula by ΔV = −∫E⃗ .d⃗ and E = constant.

By putting the value of V = Ed in eqn (i), we get:-

⟹ C = Q/Ed

⟹ C = Aϵo/d from eqn (ii).

FAQs on Electrolytic Capacitor

Question 1: Explain one electrolytic capacitor use?

Answer 1: Electrolytic capacitor is useful in circuits that involve small frequencies. One electrolytic capacitor use is smoothing the output and input to a filter.

Question 2: What is electrolytic capacitor polarity?

Answer 2: An electrolytic capacitor can be polarized, which means that they can be polarity sensitive. Furthermore, the polarized electrolytic capacitors are marked with a negative sign to clearly indicate their polarity and the negative terminal.

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