The discussion centers on the thermal management of ceramic wire wound resistors in circuits. Users are advised to verify the voltage across the resistor and consult the manufacturer's datasheet for maximum temperature ratings. While power dissipation may be within spec, resistors can still become hot due to environmental factors and proximity to other components. It is recommended to select a power resistor with a rating at least double the expected power to ensure safe operation and longevity.
PREREQUISITESElectrical engineers, hobbyists designing circuits, and anyone involved in thermal management of electronic components will benefit from this discussion.
david90 said:I have a circuit that uses a resistor to drop the input voltage. From my calculation, the power dissipation thru the resistor is less than it's wattage rating but yet the resistor is hot to the touch. Should I use a bigger resistor because it's too hot to the touch or should I keep using it because the power dissipation is within spec? The resistor is the ceramic wire wound type.
The general rule of thumb is to select a power resistor whose power rating is at least double the power it will be expected to handle.Note that the nominal power rating of a resistor is not the same as the power that it can safely dissipate in practical use. Air circulation and proximity to a circuit board, ambient temperature, and other factors can reduce acceptable dissipation significantly. Rated power dissipation may be given for an ambient temperature of 25 °C in free air. Inside an equipment case at 60 °C, rated dissipation will be significantly less; if we are dissipating a bit less than the maximum figure given by the manufacturer we may still be outside the safe operating area, and courting premature failure.