How long does a resistor last?

[Tim Williams]

On Oct 12, 11:29 am, Lostgallifreyan <no-...@nowhere.net> wrote:

I'm wondering how much of it might be due to that voltage coefficient
in carbon resistors. Maybe designers deliberately tried to reduce the effect
by careful biasing, or maybe there is a strong effect that is overlooked, I
really have no idea...

Noise?

It's well known that adding rumble and pop noise to a recording makes
it sound more appealing to the phonograph crowd. And apparently makes
them angry when you tell them that's what you've done.

You aren't going to see much nonlinearity, and resistors certainly
weren't well picked -- 470k is close enough, and with 20% resistors,
who cares anyway. What scares me more is, for instance, how a common
Magnavox 6V6 PP amp uses 0.047uF for the coupling cap to one 6V6, and
0.0047 for the other. And the phase splitter doesn't split anything,
it's just a cascaded stage. The only balancing is due to a voltage
divider. Ewwww. I'd be willing to bet they did that intentionally,
since LF distortion makes phantom bass. They used teensy output
transformers, too.

Tim

 

[Colin Trunt]

"larry moe 'n curly" <larrymoencurly@my-deja.com> wrote in message
news:e18113f3-4a77-45b7-b885-8c3b76744dbd@h40g2000prf.googlegroups.com...

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?

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)

 

[Dave Plowman (News)]

In article <iDtGm.27$ei3.8@newsfe22.ams2>,
Colin Trunt <colin@trunt.com> wrote:

"larry moe 'n curly" <larrymoencurly@my-deja.com> wrote in message
news:e18113f3-4a77-45b7-b885-8c3b76744dbd@h40g2000prf.googlegroups.com...
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?

It depends on what it is made of.
Also resistors are measured in ohms not watts.

You must be lucky if you choose them without taking into account the
current they're handling.

--
*Caution: I drive like you do.

Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.

 

[Ian Jackson]

In message <iDtGm.27$ei3.8@newsfe22.ams2>, Colin Trunt <colin@trunt.com>
writes

"larry moe 'n curly" <larrymoencurly@my-deja.com> wrote in message
news:e18113f3-4a77-45b7-b885-8c3b76744dbd@h40g2000prf.googlegroups.com...
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

 

[Arfa Daily]

"Ian Jackson" <ianREMOVETHISjackson@g3ohx.demon.co.uk> wrote in message
news:1D0mB9Nmw06KFwFy@g3ohx.demon.co.uk...

In message <iDtGm.27$ei3.8@newsfe22.ams2>, Colin Trunt <colin@trunt.com
writes

"larry moe 'n curly" <larrymoencurly@my-deja.com> wrote in message
news:e18113f3-4a77-45b7-b885-8c3b76744dbd@h40g2000prf.googlegroups.com...
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

 

[Colin Trunt]

"Dave Plowman (News)" <dave@davenoise.co.uk> wrote in message
news:50b2416ebcdave@davenoise.co.uk...

In article <iDtGm.27$ei3.8@newsfe22.ams2>,
Colin Trunt <colin@trunt.com> wrote:

"larry moe 'n curly" <larrymoencurly@my-deja.com> wrote in message
news:e18113f3-4a77-45b7-b885-8c3b76744dbd@h40g2000prf.googlegroups.com...
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?

It depends on what it is made of.
Also resistors are measured in ohms not watts.

You must be lucky if you choose them without taking into account the
current they're handling.

Not usually an issue.
Anyway I can allways stick in a resistor to drop the current
down to one it can handle. ;O)

Anyway if it lasts a day it should last a lifetime.

The usual solution is to add a heat sink.

--
*Caution: I drive like you do.

Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.

 

[Jon Elson]

Hal Murray wrote:

Depends on what it's made of and how well it's cooled. We use 0603
surface-mount resistors at half a watt, because we heat sink them
well. Half-watt carbon resistors will die at half a watt in a confined
space.

Enameled wirewounds are very tough, up until the enamel melts.

Some resistors will die from temperture cycling stress.

But in general it's good to derate 0.5 maybe.

There is another dimension to consider: duty cycle. I've been told
(but don't have first hand experience) that old fashioned carbon
composition resistors are much better at pulse loads that newer
carbon film resistors.

Proven! I was using some 100 Ohm resistors to limit current in a
spark-gap ignitor for mercury short-arc lamps. The film resistor just
BLEW off its resistance film on the first shot. I mumbled "oh yeah, I
KNEW it was going to do that" and replaced with a bulk carbon resistor,
and that held up for the life of the unit. You can guess, the pulse
current was 20,000/100 or about 100 A. 200 A ^ 2 * 100 = 4 mega-watts
for a couple microseconds.

Jon