How Much Can 2W/5W Carbon Film Resistors Be Overrated With Forced Air Cooling?

The discussion addresses the possibility of overrunning 2W and 5W carbon composition and carbon film resistors by approximately 20% using forced air cooling with powerful fans. It is generally considered feasible to increase power dissipation by about 20% under forced convection, but temperature coefficients and safety margins suggest selecting a higher power rating resistor is safer. Mounting resistors on plastic with hot glue affects heat dissipation; spacing and avoiding direct contact with plastic are recommended to prevent heat buildup. Alternatives to buying larger resistors include fabricating custom heat sinks from materials like tin or aluminum (e.g., soda cans) wrapped around the resistor, or attaching copper pieces (such as cut pennies) to resistor leads to improve heat conduction. Using resistors with integrated heat sinks, such as those available from RS Components, is another option. Measuring resistor surface temperature under free-air and mounted conditions can help determine adjusted power ratings. Immersing resistors in mineral oil, as done in amateur radio RF loads, can significantly increase dissipation capacity. High voltages (up to 600V) necessitate careful insulation and mounting choices to ensure safety.
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