Re: Higher wattage for a resistor ever bad?

On Tue, 16 Aug 2011 19:11:18 -0700 (PDT), "larry moe 'n
curly" <(E-Mail Removed)> wrote:

>When I come across a burnt resistor, I usually replace it with one
>rated for twice the wattage as the original, but I was told it's
>sometimes bad to do that. Why? I'm not referring to fuse resistors
>but ordinary carbon composition resistors.

Hmm. Not obvious why there would be a worry. The
differences amount to the following:

1) Longer body, and
2) Larger body diameter, and
3) More weight, and
3) Lower temperature at given power dissipation.

Other than the thought that it does have a fuse function,
which you dispute above, there can be:

A) The longer body or larger body diameter causes the wiring
to be too close to nearby parts, mechanically stresses
something, or blocks some hole that needs to be clear, or
B) The greater weight causes some problem (such as if it
were at the end of a propeller, for example), or
C) The lower temperature affects something else that depends
on the earlier higher temperature.

In short, I can't think of a problem that would not be pretty
obvious when you were replacing it. But then my imagination
ain't what it used to be, either.

Jon

On 8/16/2011 7:21 PM, Jon Kirwan wrote:
> On Tue, 16 Aug 2011 19:11:18 -0700 (PDT), "larry moe 'n
> curly"<(E-Mail Removed)> wrote:
>
>> When I come across a burnt resistor, I usually replace it with one
>> rated for twice the wattage as the original, but I was told it's
>> sometimes bad to do that. Why? I'm not referring to fuse resistors
>> but ordinary carbon composition resistors.
>
> Hmm. Not obvious why there would be a worry. The
> differences amount to the following:
>
> 1) Longer body, and
> 2) Larger body diameter, and
> 3) More weight, and
> 3) Lower temperature at given power dissipation.
>
> Other than the thought that it does have a fuse function,
> which you dispute above, there can be:
>
> A) The longer body or larger body diameter causes the wiring
> to be too close to nearby parts, mechanically stresses
> something, or blocks some hole that needs to be clear, or
> B) The greater weight causes some problem (such as if it
> were at the end of a propeller, for example), or
> C) The lower temperature affects something else that depends
> on the earlier higher temperature.
>
> In short, I can't think of a problem that would not be pretty
> obvious when you were replacing it. But then my imagination
> ain't what it used to be, either.
>
> Jon


If the original resistor burnt, something is wrong and needs fixed.

Replacing the resistor with a bigger one is not in any manner a solution.

--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: (E-Mail Removed)

Please visit my GURU's LAIR web site at http://www.tinaja.com

On Wed, 17 Aug 2011 08:13:16 -0700, Don Lancaster
<(E-Mail Removed)> wrote:

>On 8/16/2011 7:21 PM, Jon Kirwan wrote:
>> On Tue, 16 Aug 2011 19:11:18 -0700 (PDT), "larry moe 'n
>> curly"<(E-Mail Removed)> wrote:
>>
>>> When I come across a burnt resistor, I usually replace it with one
>>> rated for twice the wattage as the original, but I was told it's
>>> sometimes bad to do that. Why? I'm not referring to fuse resistors
>>> but ordinary carbon composition resistors.
>>
>> Hmm. Not obvious why there would be a worry. The
>> differences amount to the following:
>>
>> 1) Longer body, and
>> 2) Larger body diameter, and
>> 3) More weight, and
>> 3) Lower temperature at given power dissipation.
>>
>> Other than the thought that it does have a fuse function,
>> which you dispute above, there can be:
>>
>> A) The longer body or larger body diameter causes the wiring
>> to be too close to nearby parts, mechanically stresses
>> something, or blocks some hole that needs to be clear, or
>> B) The greater weight causes some problem (such as if it
>> were at the end of a propeller, for example), or
>> C) The lower temperature affects something else that depends
>> on the earlier higher temperature.
>>
>> In short, I can't think of a problem that would not be pretty
>> obvious when you were replacing it. But then my imagination
>> ain't what it used to be, either.
>>
>> Jon
>
> If the original resistor burnt, something is wrong and needs
> fixed.

That _may_ be the case. You don't know and neither do I. But
the OP is asking about whether or not it could be bad, so I
think it's good you point this out -- others already have,
though, so there's no need to do it twice. And I already
know, so it doesn't help telling me.

> Replacing the resistor with a bigger one is not in any
> manner a solution.

Designers aren't always perfect. Some of them are even
hobbyists or worse. These are carbon and the devices may be
old and just gradually failed -- I've seen that happen. They
do develop fissures and fail, sometimes just from vibration
sometimes from just aging or part variability that wasn't
accounted for. It _may_ be a problem elsewhere in the
circuit. It _may_ just be a failed part, itself.

I'm just glad the OP is getting all the options laid out.

Jon

On Wed, 17 Aug 2011 13:34:16 -0700, the renowned Jon Kirwan
<(E-Mail Removed)> wrote:

>
>I'm just glad the OP is getting all the options laid out.
>
>Jon

S/he should keep in mind that all absolute statements made on Usenet
are false.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
(E-Mail Removed) Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

On Wed, 17 Aug 2011 20:26:20 -0400, Spehro Pefhany
<(E-Mail Removed)> wrote:

>On Wed, 17 Aug 2011 13:34:16 -0700, I wrote:
>
>>I'm just glad the OP is getting all the options laid out.
>>
>>Jon
>
>S/he should keep in mind that all absolute statements made on Usenet
>are false.



Jon

On Wed, 17 Aug 2011 08:13:16 -0700 Don Lancaster <(E-Mail Removed)> wrote in
Message id: <(E-Mail Removed)>:

>On 8/16/2011 7:21 PM, Jon Kirwan wrote:
>> On Tue, 16 Aug 2011 19:11:18 -0700 (PDT), "larry moe 'n
>> curly"<(E-Mail Removed)> wrote:
>>
>>> When I come across a burnt resistor, I usually replace it with one
>>> rated for twice the wattage as the original, but I was told it's
>>> sometimes bad to do that. Why? I'm not referring to fuse resistors
>>> but ordinary carbon composition resistors.
>>
>> Hmm. Not obvious why there would be a worry. The
>> differences amount to the following:
>>
>> 1) Longer body, and
>> 2) Larger body diameter, and
>> 3) More weight, and
>> 3) Lower temperature at given power dissipation.
>>
>> Other than the thought that it does have a fuse function,
>> which you dispute above, there can be:
>>
>> A) The longer body or larger body diameter causes the wiring
>> to be too close to nearby parts, mechanically stresses
>> something, or blocks some hole that needs to be clear, or
>> B) The greater weight causes some problem (such as if it
>> were at the end of a propeller, for example), or
>> C) The lower temperature affects something else that depends
>> on the earlier higher temperature.
>>
>> In short, I can't think of a problem that would not be pretty
>> obvious when you were replacing it. But then my imagination
>> ain't what it used to be, either.
>>
>> Jon
>
>
>If the original resistor burnt, something is wrong and needs fixed.

Not always true. Open up a Keithley 236 or 237 (if anyone has one) and
check the 2 watt drain resistors across the main input capacitors in the
power supply. You'll likely see that they've been getting extremely hot.
In time their resistance will lower until they burn out. Hopefully the
fuse goes first, but I've seen them catch fire. Replacing them with a 3
watt resistor fixes them.

>Replacing the resistor with a bigger one is not in any manner a solution.

Not true in the case above.

On Thu, 18 Aug 2011 05:28:49 -0400, JW <(E-Mail Removed)> wrote:

>On Wed, 17 Aug 2011 08:13:16 -0700 Don Lancaster <(E-Mail Removed)> wrote in
>Message id: <(E-Mail Removed)>:
>
>>On 8/16/2011 7:21 PM, Jon Kirwan wrote:
>>> On Tue, 16 Aug 2011 19:11:18 -0700 (PDT), "larry moe 'n
>>> curly"<(E-Mail Removed)> wrote:
>>>
>>>> When I come across a burnt resistor, I usually replace it with one
>>>> rated for twice the wattage as the original, but I was told it's
>>>> sometimes bad to do that. Why? I'm not referring to fuse resistors
>>>> but ordinary carbon composition resistors.
>>>
>>> Hmm. Not obvious why there would be a worry. The
>>> differences amount to the following:
>>>
>>> 1) Longer body, and
>>> 2) Larger body diameter, and
>>> 3) More weight, and
>>> 3) Lower temperature at given power dissipation.
>>>
>>> Other than the thought that it does have a fuse function,
>>> which you dispute above, there can be:
>>>
>>> A) The longer body or larger body diameter causes the wiring
>>> to be too close to nearby parts, mechanically stresses
>>> something, or blocks some hole that needs to be clear, or
>>> B) The greater weight causes some problem (such as if it
>>> were at the end of a propeller, for example), or
>>> C) The lower temperature affects something else that depends
>>> on the earlier higher temperature.
>>>
>>> In short, I can't think of a problem that would not be pretty
>>> obvious when you were replacing it. But then my imagination
>>> ain't what it used to be, either.
>>>
>>> Jon
>>
>>
>>If the original resistor burnt, something is wrong and needs fixed.
>
>Not always true. Open up a Keithley 236 or 237 (if anyone has one) and
>check the 2 watt drain resistors across the main input capacitors in the
>power supply. You'll likely see that they've been getting extremely hot.
>In time their resistance will lower until they burn out. Hopefully the
>fuse goes first, but I've seen them catch fire. Replacing them with a 3
>watt resistor fixes them.

Well, it's obvious that using a 2W resistor is "something wrong". ;-)

>>Replacing the resistor with a bigger one is not in any manner a solution.
>
>Not true in the case above.

Our rule was 50% underrating on all carbon comps, and tantalum caps. I try to
do the same with thick-film SMTs, now.

On Thu, 18 Aug 2011 17:14:45 -0500, "(E-Mail Removed)"
<(E-Mail Removed)> wrote:

>On Thu, 18 Aug 2011 05:28:49 -0400, JW <(E-Mail Removed)> wrote:
>
>>On Wed, 17 Aug 2011 08:13:16 -0700 Don Lancaster <(E-Mail Removed)> wrote in
>>Message id: <(E-Mail Removed)>:
>>
>>>On 8/16/2011 7:21 PM, Jon Kirwan wrote:
>>>> On Tue, 16 Aug 2011 19:11:18 -0700 (PDT), "larry moe 'n
>>>> curly"<(E-Mail Removed)> wrote:
>>>>
>>>>> When I come across a burnt resistor, I usually replace it with one
>>>>> rated for twice the wattage as the original, but I was told it's
>>>>> sometimes bad to do that. Why? I'm not referring to fuse resistors
>>>>> but ordinary carbon composition resistors.
>>>>
>>>> Hmm. Not obvious why there would be a worry. The
>>>> differences amount to the following:
>>>>
>>>> 1) Longer body, and
>>>> 2) Larger body diameter, and
>>>> 3) More weight, and
>>>> 3) Lower temperature at given power dissipation.
>>>>
>>>> Other than the thought that it does have a fuse function,
>>>> which you dispute above, there can be:
>>>>
>>>> A) The longer body or larger body diameter causes the wiring
>>>> to be too close to nearby parts, mechanically stresses
>>>> something, or blocks some hole that needs to be clear, or
>>>> B) The greater weight causes some problem (such as if it
>>>> were at the end of a propeller, for example), or
>>>> C) The lower temperature affects something else that depends
>>>> on the earlier higher temperature.
>>>>
>>>> In short, I can't think of a problem that would not be pretty
>>>> obvious when you were replacing it. But then my imagination
>>>> ain't what it used to be, either.
>>>>
>>>> Jon
>>>
>>>
>>>If the original resistor burnt, something is wrong and needs fixed.
>>
>>Not always true. Open up a Keithley 236 or 237 (if anyone has one) and
>>check the 2 watt drain resistors across the main input capacitors in the
>>power supply. You'll likely see that they've been getting extremely hot.
>>In time their resistance will lower until they burn out. Hopefully the
>>fuse goes first, but I've seen them catch fire. Replacing them with a 3
>>watt resistor fixes them.
>
>Well, it's obvious that using a 2W resistor is "something wrong". ;-)
><snip>

But I think his point in telling the story is that replacing
a resistor with a higher wattage isn't _always_ masking some
other problem. Sometimes, it is fixing the _actual_ problem
at hand. He was responding to Don's absolutist claim that,
"replacing the resistor with a bigger one is not in any
manner a solution."

Jon

On Thu, 18 Aug 2011 21:05:04 -0700, Jon Kirwan <(E-Mail Removed)>
wrote:

>On Thu, 18 Aug 2011 17:14:45 -0500, "(E-Mail Removed)"
><(E-Mail Removed)> wrote:
>
>>On Thu, 18 Aug 2011 05:28:49 -0400, JW <(E-Mail Removed)> wrote:
>>
>>>On Wed, 17 Aug 2011 08:13:16 -0700 Don Lancaster <(E-Mail Removed)> wrote in
>>>Message id: <(E-Mail Removed)>:
>>>
>>>>On 8/16/2011 7:21 PM, Jon Kirwan wrote:
>>>>> On Tue, 16 Aug 2011 19:11:18 -0700 (PDT), "larry moe 'n
>>>>> curly"<(E-Mail Removed)> wrote:
>>>>>
>>>>>> When I come across a burnt resistor, I usually replace it with one
>>>>>> rated for twice the wattage as the original, but I was told it's
>>>>>> sometimes bad to do that. Why? I'm not referring to fuse resistors
>>>>>> but ordinary carbon composition resistors.
>>>>>
>>>>> Hmm. Not obvious why there would be a worry. The
>>>>> differences amount to the following:
>>>>>
>>>>> 1) Longer body, and
>>>>> 2) Larger body diameter, and
>>>>> 3) More weight, and
>>>>> 3) Lower temperature at given power dissipation.
>>>>>
>>>>> Other than the thought that it does have a fuse function,
>>>>> which you dispute above, there can be:
>>>>>
>>>>> A) The longer body or larger body diameter causes the wiring
>>>>> to be too close to nearby parts, mechanically stresses
>>>>> something, or blocks some hole that needs to be clear, or
>>>>> B) The greater weight causes some problem (such as if it
>>>>> were at the end of a propeller, for example), or
>>>>> C) The lower temperature affects something else that depends
>>>>> on the earlier higher temperature.
>>>>>
>>>>> In short, I can't think of a problem that would not be pretty
>>>>> obvious when you were replacing it. But then my imagination
>>>>> ain't what it used to be, either.
>>>>>
>>>>> Jon
>>>>
>>>>
>>>>If the original resistor burnt, something is wrong and needs fixed.
>>>
>>>Not always true. Open up a Keithley 236 or 237 (if anyone has one) and
>>>check the 2 watt drain resistors across the main input capacitors in the
>>>power supply. You'll likely see that they've been getting extremely hot.
>>>In time their resistance will lower until they burn out. Hopefully the
>>>fuse goes first, but I've seen them catch fire. Replacing them with a 3
>>>watt resistor fixes them.
>>
>>Well, it's obvious that using a 2W resistor is "something wrong". ;-)
>><snip>
>
>But I think his point in telling the story is that replacing
>a resistor with a higher wattage isn't _always_ masking some
>other problem. Sometimes, it is fixing the _actual_ problem
>at hand. He was responding to Don's absolutist claim that,
>"replacing the resistor with a bigger one is not in any
>manner a solution."

I guess a smiley wasn't enough to tip you off that the point wasn't a serious
one. Not that it surprises me that you didn't get it.

On Thu, 18 Aug 2011 23:19:27 -0500, "(E-Mail Removed)"
<(E-Mail Removed)> wrote:

>On Thu, 18 Aug 2011 21:05:04 -0700, Jon Kirwan <(E-Mail Removed)>
>wrote:
>
>>On Thu, 18 Aug 2011 17:14:45 -0500, "(E-Mail Removed)"
>><(E-Mail Removed)> wrote:
>>
>>>On Thu, 18 Aug 2011 05:28:49 -0400, JW <(E-Mail Removed)> wrote:
>>>
>>>>On Wed, 17 Aug 2011 08:13:16 -0700 Don Lancaster <(E-Mail Removed)> wrote in
>>>>Message id: <(E-Mail Removed)>:
>>>>
>>>>>On 8/16/2011 7:21 PM, Jon Kirwan wrote:
>>>>>> On Tue, 16 Aug 2011 19:11:18 -0700 (PDT), "larry moe 'n
>>>>>> curly"<(E-Mail Removed)> wrote:
>>>>>>
>>>>>>> When I come across a burnt resistor, I usually replace it with one
>>>>>>> rated for twice the wattage as the original, but I was told it's
>>>>>>> sometimes bad to do that. Why? I'm not referring to fuse resistors
>>>>>>> but ordinary carbon composition resistors.
>>>>>>
>>>>>> Hmm. Not obvious why there would be a worry. The
>>>>>> differences amount to the following:
>>>>>>
>>>>>> 1) Longer body, and
>>>>>> 2) Larger body diameter, and
>>>>>> 3) More weight, and
>>>>>> 3) Lower temperature at given power dissipation.
>>>>>>
>>>>>> Other than the thought that it does have a fuse function,
>>>>>> which you dispute above, there can be:
>>>>>>
>>>>>> A) The longer body or larger body diameter causes the wiring
>>>>>> to be too close to nearby parts, mechanically stresses
>>>>>> something, or blocks some hole that needs to be clear, or
>>>>>> B) The greater weight causes some problem (such as if it
>>>>>> were at the end of a propeller, for example), or
>>>>>> C) The lower temperature affects something else that depends
>>>>>> on the earlier higher temperature.
>>>>>>
>>>>>> In short, I can't think of a problem that would not be pretty
>>>>>> obvious when you were replacing it. But then my imagination
>>>>>> ain't what it used to be, either.
>>>>>>
>>>>>> Jon
>>>>>
>>>>>
>>>>>If the original resistor burnt, something is wrong and needs fixed.
>>>>
>>>>Not always true. Open up a Keithley 236 or 237 (if anyone has one) and
>>>>check the 2 watt drain resistors across the main input capacitors in the
>>>>power supply. You'll likely see that they've been getting extremely hot.
>>>>In time their resistance will lower until they burn out. Hopefully the
>>>>fuse goes first, but I've seen them catch fire. Replacing them with a 3
>>>>watt resistor fixes them.
>>>
>>>Well, it's obvious that using a 2W resistor is "something wrong". ;-)
>>><snip>
>>
>>But I think his point in telling the story is that replacing
>>a resistor with a higher wattage isn't _always_ masking some
>>other problem. Sometimes, it is fixing the _actual_ problem
>>at hand. He was responding to Don's absolutist claim that,
>>"replacing the resistor with a bigger one is not in any
>>manner a solution."
>
>I guess a smiley wasn't enough to tip you off that the point wasn't a serious
>one. Not that it surprises me that you didn't get it.

One can never be sure what a smiley means. And I'm kind of
proud of being literal-minded, anyway.

Jon