"Ian Jackson" wrote in message
...
In message , Colin Trunt
writes

"larry moe 'n curly" wrote in message
...
When run at its rated power?

I'm referring to 1/4 - 10 watt resistors in TVs and PC power supplies,
probably in 30-50 Celcius surrounding air.

I thought that resistors were supposed to be chosen for twice the
actual power, but I've seen many 0.5W to 1.0W resistors run at almost
exactly their rated power continuously.

Serious question?

I don't know if it is a 'serious' question, but it seems to be a perfectly
'sensible' question.

It depends on what it is made of.
Also resistors are measured in ohms not watts.
Genereally speaking the 1/2 life of the material is a good clue
as to when it#s resistance will have doubled.
SO don't use anything to radioactive.
A typical value would be a million triilion years, if it
fails before them take it back to the shop :O)

Is this a misguided attempt at humour, or have you really not the
slightest idea what you're talking about?

I suspect that the answer is very similar to that to "How long is a piece
of string", but maybe there is someone who is prepared to venture a
reasoned answer.
--
Ian

I think it depends on many factors, not the least of which are type -
w/wound, c/composition, metal film etc - how close it's being run to its
power rating, how much free circulation of air there is in the equipment,
how close it's being run to its voltage rating, and its value, depending on
type.

Resistors in high voltage circuits have a tendency to go high, for instance
anode (plate) load resistors, screen feed resistors, resevoir cap voltage
sharers or bleeders. Resistors that have a high value in the first place
i.e. above say 220k, have atendency to go high in normal use, although some
types, the old cc ones for example, are worse for this than more modern
types. Low value resistors in low voltage circuits, on the other hand,
seldom fail, unless they have done so in an obvious way - burnt out - caused
by another fault downstream of them. There is no reason at all why a
resistor in say the base bias circuit of a transistor, shouldn't last,
unchanged in characteristics, pretty much for ever. Obviously many
generalisations here, and there will of course be many anecdotal exceptions
to the rule, but I think that gives a fairly useable answer to the question.

Arfa