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| larry moe 'n curly... |
 Posted: Thu Oct 08, 2009 11:15 pm |
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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. |
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| MooseFET... |
| Posted: Fri Oct 09, 2009 2:55 am |
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On Oct 9, 2:15 am, "larry moe 'n curly" <larrymoencu... at (no spam) my-deja.com>
wrote:
[quote:bfce32e1cd]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.
[/quote:bfce32e1cd]
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. |
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| Lostgallifreyan... |
| Posted: Fri Oct 09, 2009 4:14 am |
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"larry moe 'n curly" <larrymoencurly at (no spam) my-deja.com> wrote in news:e18113f3-
4a77-45b7-b885-8c3b76744dbd at (no spam) h40g2000prf.googlegroups.com:
[quote:3e19b24523]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.
[/quote:3e19b24523]
How long is a piece of string? I think you need to rethink what you're
asking. More to endurance than duration. |
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| John Fields... |
| Posted: Fri Oct 09, 2009 5:32 am |
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On Fri, 9 Oct 2009 02:15:50 -0700 (PDT), "larry moe 'n curly"
<larrymoencurly at (no spam) my-deja.com> wrote:
[quote:fb5cbaf9d2]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.
[/quote:fb5cbaf9d2]
---
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. |
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| Frank S... |
| Posted: Fri Oct 09, 2009 6:28 am |
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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 at (no spam) austininstruments.com> wrote in message
news:a77uc5hu0idqj9jvjr2vkevpvehhk19vgf at (no spam) 4ax.com...
[quote:7f480c82a3]On Fri, 9 Oct 2009 02:15:50 -0700 (PDT), "larry moe 'n curly"
larrymoencurly at (no spam) 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.
[/quote:7f480c82a3] |
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| John Larkin... |
| Posted: Fri Oct 09, 2009 8:08 am |
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On Fri, 9 Oct 2009 02:15:50 -0700 (PDT), "larry moe 'n curly"
<larrymoencurly at (no spam) my-deja.com> wrote:
[quote:104d8c53d8]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.
[/quote:104d8c53d8]
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 |
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| larry moe 'n curly... |
| Posted: Fri Oct 09, 2009 4:36 pm |
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Lostgallifreyan wrote:
[quote:a637f4b853]
"larry moe 'n curly" <larrymoencurly at (no spam) my-deja.com> wrote in news:e18113f3-
4a77-45b7-b885-8c3b76744dbd at (no spam) 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.
[/quote:a637f4b853]
What additional information should I specify, other than rated power,
actual power, and ambient temperature? I'm not dropping high
voltages. |
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| Lostgallifreyan... |
| Posted: Fri Oct 09, 2009 9:12 pm |
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"larry moe 'n curly" <larrymoencurly at (no spam) my-deja.com> wrote in news:ef1a610c-
6d11-4fc3-96de-e00b6970c6a8 at (no spam) s21g2000prm.googlegroups.com:
[quote:a82da927bf]
Lostgallifreyan wrote:
"larry moe 'n curly" <larrymoencurly at (no spam) my-deja.com> wrote in news:e18113f3-
4a77-45b7-b885-8c3b76744dbd at (no spam) 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.
[/quote:a82da927bf]
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... |
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| Robert Baer... |
| Posted: Fri Oct 09, 2009 10:38 pm |
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larry moe 'n curly wrote:
[quote:a7ccaf4bc5]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...[/quote:a7ccaf4bc5] |
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| Robert Baer... |
| Posted: Fri Oct 09, 2009 10:40 pm |
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John Fields wrote:
[quote:059bd190ca]On Fri, 9 Oct 2009 02:15:50 -0700 (PDT), "larry moe 'n curly"
larrymoencurly at (no spam) 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[/quote:059bd190ca]
widget by 50 cents per one watt resistor used. |
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| John Fields... |
| Posted: Sat Oct 10, 2009 5:56 am |
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On Fri, 09 Oct 2009 21:40:42 -0700, Robert Baer
<robertbaer at (no spam) localnet.com> wrote:
[quote:92d9766e1d]John Fields wrote:
On Fri, 9 Oct 2009 02:15:50 -0700 (PDT), "larry moe 'n curly"
larrymoencurly at (no spam) 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.
[/quote:92d9766e1d]
---
Then your widget will cost more than an identical widget designed to be
lean, and your competition will eat your lunch. |
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| Michael A. Terrell... |
| Posted: Sat Oct 10, 2009 12:49 pm |
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John Fields wrote:
[quote:b3988a0491]
On Fri, 09 Oct 2009 21:40:42 -0700, Robert Baer
robertbaer at (no spam) localnet.com> wrote:
John Fields wrote:
On Fri, 9 Oct 2009 02:15:50 -0700 (PDT), "larry moe 'n curly"
larrymoencurly at (no spam) 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.
[/quote:b3988a0491]
And steal your dessert! ;-)
--
The movie 'Deliverance' isn't a documentary! |
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| brent... |
| Posted: Sat Oct 10, 2009 4:36 pm |
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On Oct 9, 5:15 am, "larry moe 'n curly" <larrymoencu... at (no spam) my-deja.com>
wrote:
[quote:e1a87f7f98]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.
[/quote:e1a87f7f98]
http://www.youtube.com/watch?v=Jhjb4P_jnKk |
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| Robert Baer... |
| Posted: Sun Oct 11, 2009 1:54 am |
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brent wrote:
[quote:79a4b6425d]On Oct 9, 5:15 am, "larry moe 'n curly" <larrymoencu... at (no spam) 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[/quote:79a4b6425d]
last up to 50 years... |
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| Lostgallifreyan... |
| Posted: Sun Oct 11, 2009 2:13 am |
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Guest
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Robert Baer <robertbaer at (no spam) localnet.com> wrote in
news:dsGdnej0YOnJEkzXnZ2dnUVZ_hFi4p2d at (no spam) posted.localnet:
[quote:9bfdfd2f77]brent wrote:
On Oct 9, 5:15 am, "larry moe 'n curly" <larrymoencu... at (no spam) 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...
[/quote:9bfdfd2f77]
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. |
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