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Wire wound resistor
Sep 21, 2017

Wire wound resistor

Wire wound resistor definition

Wire wound resistor is a type of passive component in which metal wires are used to reduce or restrict the flow of electric current to a certain level.

Construction of wire wound resistor

The wire wound resistor is made by winding the metal wire around a metal core. In wire wound resistors, metal wire is used as the resistance element and metal core is used as the non-conductive material.

A Nichrome or manganin is commonly used as the metal wires, because they provide high resistance to the electric current and operates at high temperature. Most commonly used core materials include plastic, fiberglass, or ceramic.

Wire wound resistor is a type of passive component, which uses metal wires to reduce or restrict the flow of electric current to a certain level.

The wounded wire is covered with an insulating material such as vitreous enamel, which opposes or blocks the outside heat. This step is taken to achieve high stability. Hence, even at high temperature heat does not enter into the wire wound resistor. Thus, the wire wound resistors operates at high temperature.

The wire wound resistors can range from small surface mount components to a large tubular power resistor. These resistors are used in the electronic instruments and equipments where high accuracy and more power dissipation are required. The wire wound resistor is more preferred over the metal oxide resistors because of its high stability at higher temperature and smaller size.

Resistance of the wire wound resistor is depends on three factors: resistivity of the metal wire, length of the metal wire and cross sectional area of the metal wire

The resistance of the wire wound resistor is depends on the resistivity of the metal wire, length of the metal wire, and cross sectional area of the metal wire.

Resistivity of the metal wire

The resistance of the wire wound resistor is directly proportional to the resistivity of the metal wire.

A metal wire with high resistance opposes or blocks large amount of electric current. Therefore, the wire wound resistor provides high resistance to the electric current.

On the other hand, a metal wire with low resistance blocks small amount of electric current. Therefore, the wire wound resistor provides low resistance to the electric current.

Length of the metal wire

The resistance of the wire wound resistor is directly proportional to the length of the metal wire.

The long length metal wires offer high resistance because the free electrons have to travel large distance. Hence, the possibility of electrons collision with the atoms is high. Therefore, a large number of free electrons collide with the atoms. The large number of free electrons colliding with the atoms loses their energy in the form of heat and the remaining small number of free electrons moves freely by carrying the electric current. Therefore, only a small number of free electrons or small amount of electric current flows through the wire wound resistor.

The short length metal wires offer low resistance because the free electrons have to travel only a small distance. Hence, the possibility of electrons collision with the atoms is low. Therefore, only a small number of free electrons collide with the atoms. The small number of free electrons colliding with the atoms loses their energy in the form of heat and the remaining large number of free electrons moves freely by carrying the electric current. Therefore, large amount of electric current flows through the wire wound resistor.

Cross sectional area of the metal wire

The resistance of a wire wound resistor is inversely proportional to the cross sectional area of the metal wire.

The metal wires with small cross sectional area provides less space for the free electrons to move. Hence, the possibility of electrons collision with the atoms is high. Therefore, only a small electric current flows through the wire wound resistor.

The metal wires with large cross sectional area provide enough space for the free electrons to move freely. Hence, the possibility of electrons collision with the atoms is low. Therefore, large electric current flows through the wire wound resistor.

Types of wire wound resistors

The wire wound resistors are classified into two types:

  • Power wire wound resistor

  • Precision wire wound resistor

  • Power wire wound resistor

Power wire wound resistors are the non-inductive wire wound resistors operates at high temperature. These resistors are commonly used for high power applications.

  • Precision wire wound resistor

Precision wire wound resistor operates at low temperature with high accuracy. It is used as a precision resistor in instrumentation because of its high accuracy.

Applications of wire wound resistors

The wire wound resistors are widely used for various applications such as:

  • Telecommunication

  • Computers

  • Audio and video equipments

  • Medical electronic equipments

  • Defense and space

  • Telephone switching systems

  • Transducers instrumentation

  • Current and voltage balancing

  • Current sensing

Advantages and disadvantages of wire wound resistor

Advantages of wire wound resistor

  • Low cost

  • High accuracy

  • High stability

  • Wide resistance range

Disadvantages of wire wound resistor

The wire wound resistors are used only for low frequencies, it is not suitable for high frequencies. At high frequencies, it acts as inductor. Hence, for high frequencies non-inductive wire wound resistors are used.