How long does a resistor last?

  • Thread starter larry moe 'n curly
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larry moe 'n curly

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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.
 
"larry moe 'n curly" <larrymoencurly@my-deja.com> wrote in 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.
Click to expand...
How long is a piece of string? I think you need to rethink what you're
asking. More to endurance than duration.
 
On Fri, 9 Oct 2009 02:15:50 -0700 (PDT), "larry moe 'n curly"
<larrymoencurly@my-deja.com> wrote:

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.
Click to expand...
---
That's because it costs more to use a larger resistor than is necessary.

Let's say that you can get 1/2 watt resistors for a penny in quantities
of a million, and one watters for 1.5 cents.

If the 1/2 watters will do the job like they're supposed to and you buy
a million one watters instead, you've just thrown away $5000.00.
 
Designing for longevity is a thing of the past. Making a buck is. Most
problems in electronics is caused by under rated components (not enough
power or voltage headroom). Caps are a big culprit.

"John Fields" <jfields@austininstruments.com> wrote in message
news:a77uc5hu0idqj9jvjr2vkevpvehhk19vgf@4ax.com...
On Fri, 9 Oct 2009 02:15:50 -0700 (PDT), "larry moe 'n curly"
larrymoencurly@my-deja.com> wrote:

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.

---
That's because it costs more to use a larger resistor than is necessary.

Let's say that you can get 1/2 watt resistors for a penny in quantities
of a million, and one watters for 1.5 cents.

If the 1/2 watters will do the job like they're supposed to and you buy
a million one watters instead, you've just thrown away $5000.00.
Click to expand...
 
On Fri, 9 Oct 2009 02:15:50 -0700 (PDT), "larry moe 'n curly"
<larrymoencurly@my-deja.com> wrote:

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.
Click to expand...
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.

John
 
On Oct 9, 2:15 am, "larry moe 'n curly" <larrymoencu...@my-deja.com>
wrote:
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.
Click to expand...
The life at rated wattage will depend on many factors. The legs of
the resistor will conduct the heat away. How much copper they hook to
will control how well this works. The brand of the resistor also
matters. One from Uncle Chin's Resistor Company will last much longer
than those from the Shaw Dee Resistor Factory because Uncle Chin uses
better ceramic.

If you use that urethane conformal coating that the US navy seems to
like so much, it will turn dark and look very ugly long before the
resistor fails. The ceramic materials will do their best when clean.
 
"larry moe 'n curly" <larrymoencurly@my-deja.com> wrote in news:ef1a610c-
6d11-4fc3-96de-e00b6970c6a8@s21g2000prm.googlegroups.com:

Lostgallifreyan wrote:

"larry moe 'n curly" <larrymoencurly@my-deja.com> wrote in 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.

How long is a piece of string? I think you need to rethink what you're
asking.

What additional information should I specify, other than rated power,
actual power, and ambient temperature? I'm not dropping high
voltages.
Click to expand...
Materials. What I was getting at is that resistors aren't always nicely
behaved metal/ceramic thingers, and carbonisation of an epoxy or urethane or
other coating might affect a high-value resistance enough to consider it
failed even though the resistive element is fine. Basically it can get
complicated, so you need to think of the specific conditions to eliminate
guesswork.

Another way of looking at it is, if it's a ceramic/metal type and isn't
glowing with heat, or melting solder if mounted that way, then it's likely to
outlast everything else in the circuit and is therefore the least of
concerns...
 
Lostgallifreyan wrote:
"larry moe 'n curly" <larrymoencurly@my-deja.com> wrote in 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.

How long is a piece of string? I think you need to rethink what you're
asking.
Click to expand...
What additional information should I specify, other than rated power,
actual power, and ambient temperature? I'm not dropping high
voltages.
 
larry moe 'n curly wrote:
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.
Resistors can last for well over 100 years...
Click to expand...
 
John Fields wrote:
On Fri, 9 Oct 2009 02:15:50 -0700 (PDT), "larry moe 'n curly"
larrymoencurly@my-deja.com> wrote:

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.

---
That's because it costs more to use a larger resistor than is necessary.

Let's say that you can get 1/2 watt resistors for a penny in quantities
of a million, and one watters for 1.5 cents.

If the 1/2 watters will do the job like they're supposed to and you buy
a million one watters instead, you've just thrown away $5000.00.

...only if you are stupid enough to not increase the sale price of the
Click to expand...
widget by 50 cents per one watt resistor used.
 
On Fri, 09 Oct 2009 21:40:42 -0700, Robert Baer
<robertbaer@localnet.com> wrote:

John Fields wrote:
On Fri, 9 Oct 2009 02:15:50 -0700 (PDT), "larry moe 'n curly"
larrymoencurly@my-deja.com> wrote:

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.

---
That's because it costs more to use a larger resistor than is necessary.

Let's say that you can get 1/2 watt resistors for a penny in quantities
of a million, and one watters for 1.5 cents.

If the 1/2 watters will do the job like they're supposed to and you buy
a million one watters instead, you've just thrown away $5000.00.

..only if you are stupid enough to not increase the sale price of the
widget by 50 cents per one watt resistor used.
Click to expand...
---
Then your widget will cost more than an identical widget designed to be
lean, and your competition will eat your lunch.
 
John Fields wrote:
On Fri, 09 Oct 2009 21:40:42 -0700, Robert Baer
robertbaer@localnet.com> wrote:

John Fields wrote:
On Fri, 9 Oct 2009 02:15:50 -0700 (PDT), "larry moe 'n curly"
larrymoencurly@my-deja.com> wrote:

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.

---
That's because it costs more to use a larger resistor than is necessary.

Let's say that you can get 1/2 watt resistors for a penny in quantities
of a million, and one watters for 1.5 cents.

If the 1/2 watters will do the job like they're supposed to and you buy
a million one watters instead, you've just thrown away $5000.00.

..only if you are stupid enough to not increase the sale price of the
widget by 50 cents per one watt resistor used.

---
Then your widget will cost more than an identical widget designed to be
lean, and your competition will eat your lunch.
Click to expand...

And steal your dessert! ;-)


--
The movie 'Deliverance' isn't a documentary!
 
On Oct 9, 5:15 am, "larry moe 'n curly" <larrymoencu...@my-deja.com>
wrote:
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.
Click to expand...
http://www.youtube.com/watch?v=Jhjb4P_jnKk
 
brent wrote:
On Oct 9, 5:15 am, "larry moe 'n curly" <larrymoencu...@my-deja.com
wrote:
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.

http://www.youtube.com/watch?v=Jhjb4P_jnKk
oh, i forgot to mention that the old wet electrolytics were known to
Click to expand...
last up to 50 years...
 
Robert Baer <robertbaer@localnet.com> wrote in
news:dsGdnej0YOnJEkzXnZ2dnUVZ_hFi4p2d@posted.localnet:

brent wrote:
On Oct 9, 5:15 am, "larry moe 'n curly" <larrymoencu...@my-deja.com
wrote:
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.

http://www.youtube.com/watch?v=Jhjb4P_jnKk
oh, i forgot to mention that the old wet electrolytics were known to
last up to 50 years...
Click to expand...
Common knowlege to me. :) It's kind of what amazes me about electrolytics. So
much variation in lifetime, I'm surprised that there are so many short-lived
ones, I'd have thought that good answers were so long out of patent that it
would be a no-brainer to choose ways to make them last. Maybe it had to do
with them not pushing for high capacity though, I mean, for a given size, the
capacity was a lot lower than now.

At this point, either the thread will morph into days and perhaps hundreds of
posts on the subject, or everyone will decide it's been done to death before
and there won't be any.
 
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.
Click to expand...
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.

--
These are my opinions, not necessarily my employer's. I hate spam.
 
hal-usenet@ip-64-139-1-69.sjc.megapath.net (Hal Murray) wrote in
news:DO2dnZ1gIacDNU_XnZ2dnUVZ_vudnZ2d@megapath.net:

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.
Click to expand...
They're also a lot better at high voltage. I'm just mentioning this because
when I used some for a HeNe supply current limit resistor, they really
impressed me. Most other things I tried eventually burned. Basically, a solid
mass is better than a film for HV, it seems.
 
Lostgallifreyan wrote:
hal-usenet@ip-64-139-1-69.sjc.megapath.net (Hal Murray) wrote in
news:DO2dnZ1gIacDNU_XnZ2dnUVZ_vudnZ2d@megapath.net:

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.


They're also a lot better at high voltage. I'm just mentioning this because
when I used some for a HeNe supply current limit resistor, they really
impressed me. Most other things I tried eventually burned. Basically, a solid
mass is better than a film for HV, it seems.
Click to expand...
Except for the horrible voltage coefficient. Carbon comps' resistances
decrease by about a quarter at their rated voltage. That's okay for a
HeNe, since the tube's load line is pretty steep.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net
 
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote in
news:0badnQb6Bo8xok7XnZ2dnUVZ_udi4p2d@supernews.com:

Lostgallifreyan wrote:
hal-usenet@ip-64-139-1-69.sjc.megapath.net (Hal Murray) wrote in
news:DO2dnZ1gIacDNU_XnZ2dnUVZ_vudnZ2d@megapath.net:

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.


They're also a lot better at high voltage. I'm just mentioning this
because when I used some for a HeNe supply current limit resistor, they
really impressed me. Most other things I tried eventually burned.
Basically, a solid mass is better than a film for HV, it seems.

Except for the horrible voltage coefficient. Carbon comps' resistances
decrease by about a quarter at their rated voltage. That's okay for a
HeNe, since the tube's load line is pretty steep.

Cheers

Phil Hobbs
Click to expand...
Well that's cool cos that's about all I ever use them for. :) But they were
the perfect answer in this singular case.
 
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote in
news:0badnQb6Bo8xok7XnZ2dnUVZ_udi4p2d@supernews.com:

Except for the horrible voltage coefficient. Carbon comps' resistances
decrease by about a quarter at their rated voltage.
Click to expand...
Veering swiftly offtopic... this interests me because people often rave about
the sound of valve amps. I don't mean audiophool ravings, I mean those who
like the effect especially in overdriven amps for bass guitar and other
instruments where the sound is appropriate, and very good. It's normally
attributed to the harmonic distortion and saturation effects in the valves,
but now 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...

Comments welcome, so long as they come from either experience or interest in
this subject.
 
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