Home Electrical Engineering Capacitors: Types, Definition, Specifications and Application of Capacitor

Capacitors: Types, Definition, Specifications and Application of Capacitor

In this post, you’ll learn about capacitors its types, specifications, applications and capacitance colour coding and letter code method.

Capacitors and Types

Capacitors an electrical or electronic component that stores electric charges. Basically, a capacitor consists of 2 parallel plates made up of conducting materials, and a dielectric material (air, mica, paper, plastic etc.) placed between them as shown in the figure.

Capacitor
Capacitor

Specifications of Capacitors

The specifications of capacitors are:

  1. Capacitance value
  2. Voltage rating
  3. Temperature coefficient
  4. Frequency range
  5. Dielectric constant
  6. Dielectric strength
  7. Power factor

1. Capacitance Value

The value of the capacitor is measured in terms of its capacitance value and is expressed in farads, microfarads and nanofarads.

2. Voltage Rating

Voltage rating is the operating voltage of the capacitor and it is measured in volts.

3. Temperature Co-efficient

The temperature co-efficient represents the stability in capacitance value with the change in temperature. It is expressed in ppm/°c.

4. Frequency Range

The frequency range is the maximum frequency up to which the capacitor can work safely.

5. Dielectric Constant

The dielectric constant is the property of the dielectric that affects the capacitance value. It can be defined as the ratio of capacitance.

6. Dielectric Strength

Dielectric strength is the ability of the capacitor to withstand the voltage per unit thickness of the dielectric material without breakdown. It is measured in Kv/mm or Kv/cm. It depends on the thickness of dielectric, temperature and supply frequency.

7. Power Factor

Power factor indicates the minimum loss in the capacitor. It states the fraction of input power dissipated as heat loss in the capacitor. Lower the power factor better will be the quality of the capacitor.

Reciprocal of the power factor is the quality factor (Q) of the capacitor. If the power factor is 0.001 then the quality factor (Q) is 1000. Thus higher the better the quality of the capacitor.

Read also: Types of Resistor and Their Symbols.

Types of Capacitors

Following are the three different types of capacitors:

  1. Fixed Capacitors
    1. Mica Capacitors
    2. Ceramic Capacitors
    3. Paper Capacitors
    4. Plastic Capacitors
    5. Electrolytic Capacitors
      1. Wet Type Electrolytic Capacitor
      2. Dry Type Electrolytic Capacitor
  2. Adjustable Capacitors
  3. Variable Capacitors

1. Fixed Capacitors

The capacitors whose capacitance value is fixed are known as fixed capacitors.

Fixed Capacitors Symbol
Fixed Capacitors Symbol

Ex: Mica capacitor, paper capacitor, plastic capacitor etc.

Fixed Capacitor types
Fixed Capacitor Example1

The different fixed capacitors are shown in the figure.

Fixed Capacitors types
Fixed Capacitor Example 2

Based on the dielectric material used fixed capacitors are further classified into:

  1. Mica Capacitors
  2. Ceramic Capacitors
  3. Paper Capacitors
  4. Plastic Capacitors
  5. Electrolytic Capacitors

1. Mica Capacitors

  • This types of capacitors are used as a dielectric material.
  • Mica sheets and metal foils are kept alternatively. The number of mica sheets and metal foils decides the capacitance value.
Mica Capacitors
Mica Capacitors
  • The constructional details are shown in the figure, from which it is clear that the alternate metal toils (1,3,5) and (2,4,6) are connected together to form 2 separate sets and lead wire is connected to these two sets for External connection.
  • The whole unit is placed in metal casing or encapsulated with resin.
Applications of Mica Capacitors:

These are used,

  1. In tuning and coupling circuits of radio and T.V. systems.
  2. In measuring instrument as standard capacitors.

2. Ceramic Capacitors

  • In these capacitors ceramic is used as a dielectric material.
  • Ceramic material is formed in the form thin disc or tube by mixing barium titanate, talc and magnesium silicate at different ratios.
Ceramic Capacitor
Ceramic Capacitor
  • On the surface of ceramic body metal film made of copper is coated and to this metal film lead wires are attached. The whole assembly is covered with plastic for external protection.
Applications of Ceramic Capacitors:

These are used:

  1. In-tank circuits and matching circuits.
  2. As coupling and bypass component.
  3. The filters circuit with the resistor.
  4. In the transistor circuit.
  5. In T.V. transmitters and receivers.

3. Paper Capacitors

  • The figure represents the constructional details of the paper capacitor, in which paper acts as a dielectric material.
Paper Capacitors
Paper Capacitors
  • Here the paper is placed between two aluminium metal foils and is rolled into a cylindrical shape.
  • Two lead wires are connected to metal foils for external connection.
  • The whole unit is dipped in wax and placed in a metal casing.
Applications of Paper Capacitors:

These are used:

  1. As stator in single-phase motors in table fans, grinders, water coolers etc.
  2. In filter circuits and power supply systems.

4. Plastic Capacitors

  • Constructional details of the plastic capacitor are shown in the figure, which consists of plastic as a dielectric material.
Plastic Capacitor
Plastic Capacitor
  • Two aluminium foils and plastic (polyester) film are kept alternately and rolled into a cylindrical shape.
  • Copper leads are soldered two metal foils and the whole unit is provided with resin moulding.
Applications of Plastic Capacitors:

These are used:

  1. For timing circuits
  2. In tuning circuits, and
  3. In integrated circuits

5. Electrolytic Capacitors

Electrolytic capacitors are polarized capacitors so these are used where energy with required polarity is necessary. Here oxide film obtained by a chemical reaction acts as a dielectric material.

Electrolytic capacitors are further classified into:

  1. Wet Type Electrolytic Capacitor
  2. Dry Type Electrolytic Capacitor
1. Wet Type Electrolytic Capacitor
  • Construction details are shown in the figure, which consists of aluminium rod placed in a base electrolyte placed in an aluminium container.
Wet Type Electrolytic Capacitor
Wet Type Electrolytic Capacitor
  • Now D.C. current is passed through the c, with the help of D.C. source connected between rod and container.
  • A thin film of oxide is deposited on the rod, which is connected to a positive terminal of the source. Thus rod acts as a positive terminal of the capacitor. The source is switched off when the rod is covered by oxide film completely.
  • Thus rod acts as (+)ve terminal, container as (-)ve terminal with oxide film as a dielectric material.
2. Dry Type Electrolytic Capacitor
  • Constructional details of dry-type electrolytic capacitors are shown in the figure, which contains two aluminium sheets separated by a layer of gauze separator saturated with a liquid chemical of boric acid.
Dry Type Electrolytic Capacitor (A)
Dry Type Electrolytic Capacitor (A)
  • Copper lead wires are soldered to the aluminium foils for external connection.
Dry Type Electrolytic Capacitor (B)
Dry Type Electrolytic Capacitor (B)
  • D.C. voltage is applied to the copper leads, which deposited aluminium oxide film on the foil that is connected to a positive terminal of the supply. so that foil acts as (+)ve terminal and other foil acts as (-)ve terminal.
  • Now the foils are rolled into a cylindrical shape and enclosed in an aluminium or plastic tube.
Applications of Electrolytic Capacitors:

Electrolytic capacitors are used:

  1. As filters in rectifier circuits.
  2. In T.V. and radio receivers for tuning purpose.
  3. As a bypass capacitor in amplifier circuits.

Some times tantalum (Ta) foils with Tantalum Pentoxide as dielectric are used instead of aluminium foils and the name of the capacitor becomes tantalum electrolytic capacitor. The constructional details of the tantalum capacitor are the same as the aluminium electrolytic capacitor.

The features of tantalum capacitors are:

  1. Their size is small
  2. Their capacitance value is high
  3. Longer self-life
  4. Less leakage current

2. Adjustable Capacitors

The capacitors whose value can be adjusted are known as adjustable capacitors. These are always connected either in series or in parallel with fixed capacitors. These types of capacitors are used where a small change in capacitance is required.

Adjustable Capacitors Symbol
Adjustable Capacitors Symbol

Ex: Trimmer & Padders.

Adjustable Capacitor Fig 1
Adjustable Capacitor Fig. 1

The trimmers are shown in the figure.

Adjustable Capacitor Fig. 2
Adjustable Capacitor Fig. 2

Adjustable capacitors are very small capacitors, that are used as secondary capacitors. These are connected in series or in parallel with fixed capacitors.

Adjustable Capacitor
Adjustable Capacitor

If the adjustable capacitor is connected in series with a fixed capacitor then it is called as a trimmer. If it is connected in parallel with a fixed capacitor then, it is called as padder.

Cup Type Adjustable Capacitor:

  • The figure represents the cup type trimmer/padder, in which the value of capacitance can be varied by varying the distance between the cups.
  • It contains a fixed bottom cup above which upper cup is placed with a screw, that can be either in clockwise or in anticlockwise directions.
  • By rotating screw to which upper cup is connected, the distance between the upper cup and bottom cup can be adjusted till to get the required capacitance value.
  • These cups are made up of aluminium and air acts as a dielectric material.

Applications of Adjustable Capacitors:

These are used,

  1. In coupling circuit in radio receivers.
  2. In tuning circuits for fine-tuning.

3. Variable Capacitors

The capacitors whose capacitance value can be varied continuously are called as variable capacitors.

Variable Capacitor Fig. 1
Variable Capacitor Fig. 1

The variable capacitors are shown in the figure.

Variable Capacitor Fig. 2
Variable Capacitor Fig. 2
Variable Capacitors
Variable Capacitors
  • The figure represents the constructional details of variable capacitors, which consists of 2 sets of semi-circle plates out of which one set is fixed called as a stator and another set is movably called as a rotor.
Gang Condensar
Gang Condenser
  • In these types of capacitors, the rotor is fixed to the shaft which rotates the rotor plates in or out of the fixed plates. This rotation of rotor increases or decreases the area of contact between the rotor and stator, which varies the capacitance value. When 2 or 3 sets are placed on the same shaft they are called as gang condensers or gang capacitors figure (B).

Applications of Variable Capacitors:

These are used:

  1. In radio turning circuits for selection of radio stations.
  2. In oscillator to adjust the resonant frequency.

Difference Between Trimmers & Padders

Difference Between Trimmers & Padders

Capacitance Colour Coding

Capacitors manufactured in small size are identified by their colour bands provided on their surfaces. To identify the capacitance value following steps are adopted:

  • Hold the capacitor so that colour bands should start from the left-hand side
  • Read the colour bands from left to right.
  • The first band indicates the first digit, the second band indicates the second digit, the third band indicates the multiplier or number of zeroes to be added after the second digit, the fourth band indicates the tolerance in percentage, fifth indicates temperature co-efficient and sixth band indicates working voltage.
  • The capacitance value is in picofarads (P.F.)
Capacitor Colour Coding
Capacitor Colour Coding

Capacitance Letter Code Method

Small capacitors such as a film or disk types are identified by letter code system. The code made of 2 or 3 numbers and an optional tolerance letter code. In a two-number code, the two numbers are the value of capacitor given in picofarads (i.e. 47 = 47pF). A three-letter code consists of the two value digits and a multiplier (ex: 471 = 47×10 = 470pF). Three-digit codes are usually characterised by an additional tolerance letter code as given below:

Ex: Consider the capacitor that has the code 473j printed onto its body whose value becomes,

The different codes with their capacitance value are given in the below table:

Codes
Codes

Applications of Capacitors

Capacitors are used:

  1. Capacitors used to store electrical energy.
  2. To resist the change in the applied voltage.
  3. To block d.c. and allow a.c; through it.
  4. It improves p.ſ. of a circuit.
  5. To start single-phase a.c. motor.
  6. To carry high-frequency signals and block low-frequency signals.

That’s it, thanks for reading.

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Saif M
Saif M. is a Mechanical Engineer by profession. He completed his engineering studies in 2014 and is currently working in a large firm as Mechanical Engineer. He is also an author and editor at theengineerspost.com