On Thu, 18 Aug 2011 23:19:27 -0500, "
wrote:

On Thu, 18 Aug 2011 21:05:04 -0700, Jon Kirwan
wrote:

On Thu, 18 Aug 2011 17:14:45 -0500, "
wrote:

On Thu, 18 Aug 2011 05:28:49 -0400, JW wrote:

On Wed, 17 Aug 2011 08:13:16 -0700 Don Lancaster wrote in
Message id: :

On 8/16/2011 7:21 PM, Jon Kirwan wrote:
On Tue, 16 Aug 2011 19:11:18 -0700 (PDT), "larry moe 'n
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