Analysis of the relationship between resistor operating temperature and power (1)

Recently, with the widespread application of pre-charging resistors in the field of new energy, more and more customers need to find resistors with high power and small installation size, and this change in demand has also profoundly affected the shift in the focus of our production and R&D companies. In general, the principle of pre-charging resistors is the same as that of our other original resistors, which is to convert excessive electrical energy into thermal energy. However, pre-charging resistors have different requirements from our previous main customers (brake resistors). The installation space of previous customers is generally sufficient, and there is relatively enough space for our resistor design. However, the installation space of pre-charging resistors is generally limited, and customers want the product to be as small as possible. Today we will analyze this problem from a professional perspective:

During the operation of the resistor, the resistor will emit heat to increase the ambient temperature near the resistor, which not only affects the working efficiency of the semiconductor device, but also affects the service life of the resistor due to the degree of temperature change. When we understand this corresponding relationship, we can reasonably apply power to the resistor without causing its surface temperature to rise beyond the design requirements.

First, we need to understand the heat dissipation method of the resistor:

At rated power, the resistor is an electric energy-heat energy conversion element, which consumes electric energy and converts it completely into heat energy. The electric power P dissipated by the resistor is related to the applied current I and voltage U:

P=UI=I²R=U²/R

The heat energy generated by the resistor is consumed in heating itself and dissipating heat to the surrounding medium. Therefore, the electrical load capacity of the resistor depends on the allowable heating temperature of the resistor for long-term stable operation.
Under rated power, the temperature of the resistor will no longer rise after reaching a certain temperature, and all the electric power will be dissipated to the surrounding medium. There are three ways to dissipate heat: radiation, convection and conduction. For resistors with higher power, radiation accounts for about 50%, convection accounts for about 25%, and conduction accounts for about 25%. For resistors with lower power, radiation accounts for about 10%, convection accounts for about 30%, and conduction accounts for about 60%.