Quote:
Originally Posted by tubesrule
Mass has nothing to do with terminal temperature. Mass will affect the rate of change of temperature, but thermal resistance is what determines the terminal temperature. Thermal resistance is affected by material, surface area and air flow. A larger mass will make it take longer to reach its final temperature, but that temperature will still be the same.
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Higher watt resistors typically have more surface area and thus run cooler...this goes for both chassis mount and non-chassis mount types.
A resistor of a given material typically gets rated by the amount of watts it can continuously handle without burning up or changing value (minus some percentage for headroom/safety). If the power put in is less than the power leaving that energy stays with the part and makes it hotter. If we concern our selves with a single resistance value and consider resistors of the same composition but different wattage rating, then obviously the higher rated part has a case that allows it to put energy into the air at a higher rate.
If a resistor is capable of putting thermal energy into the air at a higher rate than the circuit can supply it with energy the it will not store thermal energy and stay cool....
This can be proved empirically by taking a 1/2, 1 and a 10W resistor all of the same resistance connecting them in turn to a bench supply set to deliver 1W of power to them and observing how each responds over say 1 hours time...the 1/2W should over heat and burn open, the 1W probably get too hot to touch but remain stable and the 10W probably won't get noticably warmer than the ambient temperature of the room..... I've performed a version of this experiment before.