Cement resistors, also known as ceramic-insulated power wirewound resistors, are commonly used in various electronic devices such as computers, TVs, instruments, and audio equipment. These resistors are constructed by winding a high-power resistance wire, making them larger in size compared to standard resistors. This unique design allows for easy identification based on their physical appearance and power rating.
They come in different power ratings, including 2W, 3W, 5W, 7W, 8W, 10W, 15W, 20W, 30W, and 40W. Popular models include RX27-1, RX27-3 (available in 3A, 3B, 3C), and RX27-4 (offered in 4V, 4H). These components are typically shown in diagrams or images to help users recognize their structure and dimensions.
The construction of cement resistors uses industrial-grade ceramic shells, which provide excellent heat dissipation and insulation properties. Their insulation resistance can reach up to 100 MΩ, and they are designed with flame-retardant and explosion-proof features. The resistance wire is made from materials like constantan, manganin, or nichrome, ensuring good stability and the ability to handle overloads. The terminal connections are usually crimped, allowing the resistor to quickly break during a short circuit, thus protecting the rest of the circuit.
Cement resistors are available in multiple shapes and mounting styles. They can be directly mounted on printed circuit boards or installed using metal brackets for better positioning and heat management. This flexibility makes them suitable for a wide range of applications, especially where high power and durability are required.
When operating at room temperature, the power rating of a cement resistor can be calculated using the formula: P = V × I. However, in special environments, it’s important to refer to the power derating curve to ensure safe operation. If the resistor is subjected to high power or poor heat dissipation conditions, it’s advisable to use longer lead resistors or mount them on a metal bracket for better thermal performance.
The relationship between the power rating, resistance range, and physical dimensions of a cement resistor is illustrated in Expression 1-1. Additionally, a table showing the corresponding power, resistance values, and sizes is provided below for reference.
The power, resistance range, and corresponding dimensions of cement resistors are summarized in the following table:
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