Resistor Construction: Composition vs Wirewound

When it comes to selecting the right type of resistor for an electronic application, the choices can feel overwhelming. Wirewound resistors and composition resistors are two common options, each with its own set of advantages and disadvantages. While both are designed to regulate the flow of electrical current, their construction and materials differ. Understanding the unique properties of each can help you make an informed decision about which type of resistor is best for your project. 

This blog will explain the differences between wirewound resistors and composition resistors to help you determine which option is right for your needs.

Choosing the Right Resistor

When considering which resistor to use for a given electrical application, there are several factors to evaluate. The first is the resistance value, which should match the required resistance for the circuit to ensure proper operation. The power rating of the resistor is also critical, as it determines the maximum amount of power the resistor can safely dissipate. The tolerance of the resistor should be selected based on the precision required for the application, while the temperature coefficient of resistance should be considered if the circuit will be exposed to fluctuating conditions. In addition, the physical size and shape of the resistor should be evaluated to ensure it will fit and function properly within the circuit.

Wirewound Resistors

A resistor is any passive electrical device that limits or restricts current flow in a circuit. Wirewound resistors are typically used in high power and industrial applications such as circuit breakers and fuses because of their stability and resistance range. Wirewound resistors are produced in many wattage sizes. They are primarily used for their high precision and stability, ensuring proper performance within most circuits.

Wirewound Resistor Construction

Wirewound resistors, as their name suggests, differ from other resistive components in that they are made up of a conductive wire wrapped around a non-conductive core. The conductive wire can be made of a number of different alloys at varying thicknesses, typically nickel-chromium, manganese-copper, or constantan. The choice of alloy helps determine the resistance value. The core, on the other hand, is typically made of porcelain. While the materials are relatively standardized, the configuration can be modified any number of ways based on the resistor’s intended mount, application, and resistance range.

Composition Resistors

Like wirewound resistors, composition resistors are typically chosen for high energy applications. These resistors in particular are able to maintain high levels of energy absorption without any negative effects to the resistance value due to their mass. It makes them a robust choice for handling surge loads and other high energy events in power transformers and communications equipment. They are less precise than wirewound resistors and are generally harder to find in tighter tolerances.

Composition Resistor Construction

All composition resistors are made from a mixture of a finely ground insulator and conductor. The resistance range is determined by the ratio of this mixture. For the most common type of resistor within this category, the carbon resistor, the resistive element is composed of carbon or graphite dust and a non-conducting ceramic/clay powder. Lead may also be used as the insulative material. After being combined, the insulator/conductor mixture is compressed into a cylindrical shape, terminals are attached, and an insulation coating is applied to the outside.

Carbon is the material of choice for this class of resistor because it’s conductive, but not overly so. It can also maintain integrity under heavy electron load, making carbon composition resistors a reliable and durable choice for high voltage applications.

Resistors as a System Component

Which type of resistor is most appropriate for the application at hand depends not only on the construction of the resistor itself but also the surrounding components. From high voltage surface mount chips to high power load banks, modern industrial systems and controls require a multitude of different parts to operate reliably in tandem, under heavy load. Whether you’re stopping a train or a lightning strike, doing your due diligence on every component is a critical step in configuring mission critical systems.

Ohmite has been the leading provider of resistive products for high current, high voltage, and high energy applications for over 95 years. Our full complement of resistor construction includes wirewound, wire element, thick film, and ceramic composition. We also lead the way in thermal management for resistive and other technologies offering a vast array of heatsinks. Contact our team today to learn more.