Home - Electrical Electronic - Understanding carbon composition resistor

Understanding carbon composition resistor

Carbon composition resistors are one of the oldest types that have been around since the 1960s. there are many modern resistors that offer better performance although they are still used in some specialized applications. Also, the carbon composition resistors are of high cost and have low stability. They are known as carbon resistors or carbon composite.

carbon composition resistor

Today you’ll get to know the definition, applications, parts, diagram, construction, specifications, and working of carbon composition resistors. You’ll also get to know the advantages and disadvantages of these resistors.

Read more: Understanding resistors

What is a carbon composition resistor?

Carbon composition resistors are types of fixed resistor that produces or restricts the electric current flow to a specific limit. They are the ones available in the early 1960s and are established along with wire-wound types. Valve or tube-based are equipment used to give form to the component which makes their size much bigger. Carbon composition resistors used in the early 20th century had uninsulated bodies. The leads were wrapped around the ends of the resistive element and soldered. Newer designs had a form of the ceramic body to protect them.

Many materials such as nichrome, brass, platinum, and tungsten, which are metal, and alloys are used to produce the resistance. However, they have low resistance compared to carbon resistors because it makes it difficult to produce high resistance without making the resistor bulky. You should know that resistance is directly proportional to the product of the length and resistivity of the resistor. Carbon resistors can produce a high accuracy value of resistance and it is usually used to calibrate the resistance.

Read more: Understanding ultracapacitors

Applications of a carbon composition resistor

Although the use of carbon composition resistors is not common these days there are some applications for which they are well suited. These can be seen from their ability to absorb high transient without the risk of damage that newer resistors might face. Because carbon resistors hold up well at high energy levels, they are often used in power supply applications including high voltage uses like the one used by an electrical utility provider, and lower voltage applications just like a simple power strip-style surge protector or other home electronics. Some other applications of carbon composition welding include:

  • Welding controls
  • High-frequency applications since their construction do not introduce inductance.
  • Other protection circuits
  • Current limiting circuits
  • Surge protection circuits.

In addition, carbon composition resistors were used in many valves or tube-based equipment such as radios and television sets to more professional forms of electronic equipment. They are capable of withstanding the operating environment of the equipment for which they are used, but when compared with today’s standards they perform very poorly.

Parts

Parts of a conventional carbon composition resistor include carbon mixture, connecting leads for both sides, color codes, end caps, and insulating materials. All these components are explained in the video below.

Diagram of a carbon composition resistor:

Diagram and construction of carbon composition resistor insulating material. Normally, this material is ceramic and a resin is used to bind the mixture together and it was pressed into small rods under heat. Leads are added after the construction of the carbon composition rods. This is achieved by pressing leads into either end of the rods, or by using metal caps attached to either end onto which wires are added.

The rods are baked before adding a coating. This is because the rods are very porous and cannot resist moisture, dirt, and grease which can degrade their performance. Although some resistors are not coated, well most do and typically consist of a ceramic cylindrical coating around the resistor. The resistance can be changed by altering the composition of the graphite mix in the rods or extending them. wider rods will make the power dissipation capability increase, but it also decreases the resistance for a given mix.

These resistors are very difficult to have a given tolerance value which leads to sorting after manufacture. Typical tolerance was ±20%, although ±10% and occasionally ±5% versions were available.

Specifications

The table below shows the performance of carbon composition resistors:

CARBON COMPOSITION RESISTOR PARAMETER CARBON COMPOSITION RESISTOR PERFORMANCE
Typical tolerance availability ±5%, ±10%, ±20%
Value range 1Ω – ~10MΩ
Load life (% change over 1000h) +4
Max noise (µV/V) 6
Temperature coefficient (ppm/°C) >±1000
Voltage coefficient (%/V) 0.05
Max resistor temperature (°C) 120

Watch the video below to learn more about carbon composition resistors:

Advantages and disadvantages of carbon composition resistors

Advantages:

Even though the carbon composition resistors have been for a long, they are used only on specific applications due to their limitations. Below are the benefits of carbon composition resistors in their various applications:

High energy pulse capability:

The carbon composition resistors are capable of withstanding much higher energy pulses than most other types. The resistive rod has a much larger size, which is why they are able to absorb more energy than the film types that are commonly used today. With this, they are sometimes used on applications where high-energy pulses occur.

Disadvantages:

Below are the limitations of carbon composition resistors in their various applications:

Stability:

Carbon composition resistors have a very poor level of performance when it comes to stability. Their value of resistance could change by as much as 5% in a year even if they are not in use. This could be as a result of heat, in fact, soldering could change the value by 2 or 3% and temperature of about 70% can alter the value by 15% or even more.

Noise:

Noise is another limitation of a carbon composition resistor. This is due to the granular composition and structure of the resistive element. Other disadvantages include:

  • High-temperature coefficient:
  • Low accuracy
  • Larger sizes took circuit board space

That is all for this article where the definition, applications, parts, diagram, construction, specifications, and working of carbon composition resistors are being explained. Their advantages and disadvantages are also discussed. I hope you got a lot from the reading, if so, kindly share with other students. Thanks for reading, see you next time!

Join our Newsletter

Leave a Reply

Your email address will not be published.