Basic principles and applications of carbon composite resistors
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Basic principles and applications of carbon composite resistors

Posted Date: 2024-02-04

Carbon composition resistors, often called carbon composite resistors or even carbon composite resistors are an older type of resistor that are not used in new equipment today.

Over the years, these carbon composition resistors have been used as the primary resistor type in many valve- or tube-based devices, from radios and televisions to more professional forms of electronic equipment.

Carbon composition resistors are capable of withstanding the operating environment of the equipment in which they are used, but their performance is poor in several aspects compared to today's standards.

Carbon Composition Resistor Timetable

Carbon combination resistors or carbon composite resistors were one of the first resistor types established along with the wirewound type. They continued to be used in various forms until the 1960s, particularly in valve- or tube-based equipment where size was not particularly important. In the 1960s, as more transistor devices were introduced, requiring smaller, better-performing resistors, the use of carbon composition resistors gradually declined, being replaced by carbon film or later metal oxide film resistors, although they were used for some professional applications.

Carbon composition resistors dating back to the early 20th century have non-insulators. The leads are wrapped around the end of the resistor element and soldered. The completed resistor is colored to provide a coding of its value.

Later models had a form of ceramic body to protect them. These are generally the more familiar and tend to be used in many older tube/tube radios.

Carbon composition resistor structure

The main resistive element within a carbon composition resistor is made from a mixture of finely ground or powdered carbon with insulating materials (usually ceramics and resins) to bind the mixture together. Press the mixture over heat into small sticks.

After manufacture, lead is added to the carbon component rods. This is done by pressing the leads into the ends of the rod, or using metal caps attached to the ends to which the wires are added.

The rod is baked and then the next stage is to add the coating, as the rod itself is very porous and will absorb moisture, dirt and grease, thus changing properties.

While some resistors sometimes come without a coating, most resistors do, usually consisting of a ceramic cylindrical coating around the resistor.

The resistance is changed by changing the composition of the graphite mixture in the rods or lengthening them. Power dissipation capabilities are increased by making the rods wider, although this also reduces the resistance for a given mix.

Given manufacturing tolerances, it is difficult to manufacture them to the given values. Instead, they are sorted after they are manufactured. Typical tolerances are only ±20%, but ±10% and occasionally ±5% versions are available.

Carbon composition resistor types are manufactured in 1/4, 1/2, 1 watt values ​​and in some cases up to 5 watts.

Advantages and Disadvantages of Carbon Composition Resistors

Due to the disadvantages of carbon composition resistors, they are rarely used today. However, carbon composition resistors do have some advantages, so it is still used in some professional applications.

Advantage:

High Energy Pulse Capability: Carbon composite resistors, or carbon composition resistors, are capable of withstanding much higher energy pulses than most other types of resistors available today. Resistor rods are much larger in size than the thin film types more commonly used in electronic components and are able to absorb more energy. Therefore, they are sometimes used in areas where high-energy pulses may be present.

Disadvantages:

Stability: Carbon composition resistors have very poor performance levels in terms of stability. Even without use, resistance values ​​may change by as much as 5% over a year. Heat may also change this value. Welding can change this value by 2% or 3%, and operating at temperatures up to 70°C may change this value by 15% or more.

High Temperature Coefficient: Carbon composite resistors also exhibit very low temperature stability. Stability figures below 1000 ppm/°C are expected.

Noise: Carbon components are very noisy due to the grain composition and structure of the resistive element. Other forms of resistors are much better.

Carbon composition resistor applications

Although carbon composition resistors are not widely used today, they are well suited for certain applications. This is usually due to their ability to absorb high transients without the risk of damage that other resistors may suffer.

surge protection circuit
current limiting circuit
Other protection circuits
Welding control

Some high frequency applications because their structure does not introduce inductance

Although carbon composition resistors are relatively simple to construct and have been established for many years, their lower usage means they are more of a specialty product and cost more than other types, although they are still relatively cheap.

Typical Carbon Composition Resistor Specifications

Typical performance data for carbon composition resistors are given below as a performance guide

Carbon Composition Resistor Performance Guide

Carbon composition resistance parameters

Carbon Composition Resistor Performance

Typical tolerance availability

±5%、±10%、±20%

Ranges

1Ω - ~10MΩ

Load life (percentage change above 1000h)

+4

Maximum noise (μV/V)

6

Temperature coefficient (ppm/°C)

>±1000

Voltage coefficient (%/V)

0.05

Maximum resistance temperature (°C)

120


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