Carbon composition resistor

 
Carbon composition resistor

An introduction to carbon composition resistors Carbon composition resistors (CCR) are fixed form resistors. They are made out of fine carbon particles mixed with a binder (for example clay). After baking it has a solid form. Although carbon composition resistors are widely applied in circuits, the majority of resistors are nowadays  made by deposition of a metal or carbon film over a ceramic carrier. Advantages and disadvantages The big advantage of carbon composition resistors is their ability to withstand high energy pulses. When current flows through the resistor, the entire carbon composition body conducts the energy. The wirewound resistor for example, has a much smaller volume of the wire to conduct.  So the thermal mass of the carbon composition resistor is much higher, resulting in a higher energy capability.  Carbon resistors can be made with a higher resistance than wirewound resistors, and are considerably cheaper. However, the properties are less good in terms of temperature coefficient, noise, voltage dependence and load. Fifty years ago, carbon composition resistors were widely used in consumer electronics. Because of the low stability of the resistance value, this type of resistor is not suitable for any modern high precision application. For example, the resistance value can change up to 5% over a shelf life of one year.  With heavy use the value changes even more: up to 15% for a 2000h test at full rating with 70°C. Soldering can cause a 2% change. The reason for this instability is inherent to the design of the resistor. The carbon composition contains materials with different heat expansion properties. When the conducting carbon particles and the nonconducting binder heat up or cool down, stresses arise in the resistor body. The mechanical contact between the conducting particles will change, and this leads to a change in resistance value. Also [… read more]