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Re: Electronics 101 Question .....
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Posted by Gerald J. on October 25, 2006 at 19:39:57 from (67.0.102.127):
In Reply to: Re: Electronics 101 Question ..... posted by Bob/Ont on October 25, 2006 at 19:00:10:
No. The temperature rise of the resistor depends only on the cooling area of the resistor. A resistor reaches its maximum rated temperature rise with rated power dissipated. That is independent of voltage, current, or resistance. A resistor will have a temperature rise proportional to the actual power disspated times the rated temperature rise divided by the rated power. So if the dissipated power is smaller than the rated power the temperature rise will be small. If the dissipated power is larger than the rated power the temperature rise will be large and it depends on the construction of the resistor whether that resistor will smoke or will survive. Vitrious glass coated wire wound resistors on ceramic cores can take a few times rated power, but they may melt the glass and that glass dripping on adjacent objects may ignite the surroundings. Tin oxide film resistors I've found can handle ten times rated power, but they glow and the heat radiated can ignite adjacent objects like plastic cases or fiberglass-epoxy printed circuit boards. Old carbon composition resistors will smoke at not much above their rated power and will drift in resistance just from the passage of time, though heat and humidity will speed up the drift in resistance. Gerald J.
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