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Higher wattage for a resistor ever bad?
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. |
Higher wattage for a resistor ever bad?
larry moe 'n curly 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. Sometimes, ordinary resistors ARE used as fusable. Anything to save a cent, or a fraction of a cent anyway. -- Abandon all hope ye who have entered cyberspace. |
Higher wattage for a resistor ever bad?
On Tue, 16 Aug 2011 19:11:18 -0700 (PDT), "larry moe 'n
curly" 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 |
Higher wattage for a resistor ever bad?
larry moe 'n curly 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. No. The first step of repairing this thing is diagnosing what caused the first one to fail. If it was just a failure of the part itself, then the replacement only needs to be as big as the original, albeit one of higher wattage rating can do no harm - the thing is, if you use that (higher wattage R) without knowing what caused the first one to burn up, you might be masking a more fundamental problem. Hope This HElps! Rich |
Higher wattage for a resistor ever bad?
larry moe 'n curly 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. Resistors mostly cook due to two reasons - 1) Under-specked. Runs too hot for the application. Good idea in this case. 2) (Most common reason) Something else failed and pulled excessive current through the resistor. If you replace just the resistor, and use a higher wattage part, you might cook other (more expensive) stuff. Lord Valve American - so far |
Higher wattage for a resistor ever bad?
"larry moe 'n curly" wrote in message ... 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. No, it shouldn't be a problem. Different wattage is usually associated with size. If the resistor was 'cooked' then it was running at or beyond it's rating. Which means there was something else in the circuit that is defective. Most resistors are metal film nowadays, carbon comps are hard to come by. (But Carbon comps do handle peak currents much better than metal films.) Cheers |
Higher wattage for a resistor ever bad?
On Tue, 16 Aug 2011 19:11:18 -0700 (PDT), "larry moe 'n curly"
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. A larger resistor may have different stray inductances and capacitances, which might affect some RF circuits. |
Higher wattage for a resistor ever bad?
"larry moe 'n curly" 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. ** Carbon comp resistors are rare and almost obsolete these days - did you mean carbon film ? Most resistor burn ups are the result of misuse or OTHER failures in the equipment, so no upgrade is needed If a new resistor of the same size gets unusually hot, then an upgrade is justified. BTW 2 and 3 watt carbon comp resistors that run hot ( 100C or more ) gradually fall in value and get even hotter, ie a vicious cycle exists until complete failure occurs. Replace them with a wire wound type. ..... Phil |
Higher wattage for a resistor ever bad?
On Aug 17, 12:41*pm, "Martin Riddle" wrote:
"larry moe 'n curly" wrote in ... 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. No, it shouldn't be a problem. Different wattage is usually associated with size. If the resistor was 'cooked' then it was running at or beyond it's rating. Which means there was something else in the circuit that is defective. Most resistors are metal film nowadays, carbon comps are hard to come by. (But Carbon comps do handle peak currents much better than metal films.) Carbon composition resistors have a negative temperature coefficient of resistance - put enough current through them and you form a "hot channel" with almost all the current being carried by thin filament that is almost incandescent, and presents a very low resistance. Back in 1974, my then boss amazed me - and several other engineers - by persuading a nominally 10k carbon film resistor to pass something like an amp with a voltage drop of about 100mV for about half an hour. There was a very narrow stripe of discoloured paint above the hot channel, but that was the only evidence of what was going on. He been having trouble with an "intrinsic safety" standards committee, and this demonstration (and a couple of repeat performances) managed to persuade them that carbon film and carbon composition resistors had to be banned in intrinsicly safe devices. -- Bill Sloman, Nijmegen |
Higher wattage for a resistor ever bad?
On Tue, 16 Aug 2011 22:41:21 -0400, "Martin Riddle"
wrote: "larry moe 'n curly" wrote in message ... 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. No, it shouldn't be a problem. Different wattage is usually associated with size. If the resistor was 'cooked' then it was running at or beyond it's rating. Which means there was something else in the circuit that is defective. Most resistors are metal film nowadays, carbon comps are hard to come by. http://www.ohmite.com/cgi-bin/showpa...t=little_demon http://www.seielect.com/Catalog/SEI-rc.pdf http://search.digikey.com/scripts/Dk....dll?Cat=66690 -- JF |
Higher wattage for a resistor ever bad?
On Tue, 16 Aug 2011 19:11:18 -0700 (PDT), the renowned "larry moe 'n
curly" 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. The safest thing is to use an exact replacement unless you understand the circuit more than well enough to have designed it in the first place. Or get an ECO that allows the use of the substitute part. Replacing a current-sense resistor with the wrong type (too inductive) could cause a whole lot of pain, for example. If you actually are talking about carbon composition resistors (fairly uncommon and relatively expensive these days, as others have said), then there isn't much problem with a higher wattage other than getting it to fit, but most resistors these days are metal film (with some carbon film still around in through-hole applications, and wirewound used in power applications). There's also metal foil, fusible, high voltage rating, metal-oxide-film (MOF), tight tolerance, low tempco, positive TCR, low inductance, and lots of other types of resistors. Wattage rating is only one parameter (and it really isn't a simple parameter- it might be lower in a given application than the big print value if you limit how hot the body of the resistor can get or limit the ambient temperature or have pulses of current that yield high peak power). Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com |
Higher wattage for a resistor ever bad?
Martin Riddle wrote:
Most resistors are metal film nowadays, carbon comps are hard to come by. .... Nah, all the major parts houses in the USA carry 'em...Mouser, Digi-Key, etc. Hell, you can even get 'em as SMDs. LV |
Higher wattage for a resistor ever bad?
On Wed, 17 Aug 2011 06:31:29 -0600, Lord Valve
wrote: Martin Riddle wrote: Most resistors are metal film nowadays, carbon comps are hard to come by. ... Nah, all the major parts houses in the USA carry 'em...Mouser, Digi-Key, etc. Hell, you can even get 'em as SMDs. LV "Most" (by far) by quantity used, but even by types offered, fewer than 3% of the resistor part numbers that Digikey has in stock are carbon comp. |
Higher wattage for a resistor ever bad?
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. 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: Please visit my GURU's LAIR web site at http://www.tinaja.com |
Higher wattage for a resistor ever bad?
On Wed, 17 Aug 2011 08:13:16 -0700, Don Lancaster
wrote: 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. 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 |
Higher wattage for a resistor ever bad?
On Wed, 17 Aug 2011 13:34:16 -0700, the renowned Jon Kirwan
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" Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com |
Higher wattage for a resistor ever bad?
On Wed, 17 Aug 2011 20:26:20 -0400, Spehro Pefhany
wrote: On Wed, 17 Aug 2011 13:34:16 -0700, the renowned Jon Kirwan 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. --- How firmly do you believe that? ;) -- JF |
Higher wattage for a resistor ever bad?
On Wed, 17 Aug 2011 20:26:20 -0400, Spehro Pefhany wrote:
On Wed, 17 Aug 2011 13:34:16 -0700, the renowned Jon Kirwan 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. Absolutely. -- www.wescottdesign.com |
Higher wattage for a resistor ever bad?
On Aug 17, 8:26*pm, Spehro Pefhany
wrote: On Wed, 17 Aug 2011 13:34:16 -0700, the renowned Jon Kirwan 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. That's totally wrong. George H. Best regards, Spehro Pefhany -- "it's the network..." * * * * * * * * * * * * *"The Journey is the reward" * * * * * * Info for manufacturers:http://www.trexon.com Embedded software/hardware/analog *Info for designers: *http://www.speff.com |
Higher wattage for a resistor ever bad?
On Wed, 17 Aug 2011 20:26:20 -0400, Spehro Pefhany
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 |
Higher wattage for a resistor ever bad?
Got any penneys to replace a blown fuse? |
Higher wattage for a resistor ever bad?
In article ,
"Phil Allison" wrote: "larry moe 'n curly" 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. ** Carbon comp resistors are rare and almost obsolete these days - did you mean carbon film ? Most resistor burn ups are the result of misuse or OTHER failures in the equipment, so no upgrade is needed If a new resistor of the same size gets unusually hot, then an upgrade is justified. BTW 2 and 3 watt carbon comp resistors that run hot ( 100C or more ) gradually fall in value and get even hotter, ie a vicious cycle exists until complete failure occurs. Replace them with a wire wound type. Which may or may not prevent oxidation of the solder joints and/or damage to the circuit board where the resistor connects. I've seen many instances where the power rating of the resistor was fine *for the resistor* but not for the board it was mounted on. Isaac |
Higher wattage for a resistor ever bad?
Under-specked is one matter, but I'd be more worried about over-striped.. or
is that a hearse of a different color? -- Cheers, WB .............. "Lord Valve" wrote in message ... 1) Under-specked. Runs too hot for the application. Good idea in this case. 2) (Most common reason) Something else failed and pulled excessive current through the resistor. If you replace just the resistor, and use a higher wattage part, you might cook other (more expensive) stuff. Lord Valve American - so far |
Higher wattage for a resistor ever bad?
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. Replacing the resistor with a bigger one is not in any manner a solution. Not true in the case above. |
Higher wattage for a resistor ever bad?
"Ron D." wrote: Got any penneys to replace a blown fuse? Do you mean 'Pennies', or the department store? -- Subject: Spelling Lesson The last four letters in American.........I Can The last four letters in Republican.......I Can The last four letters in Democrats.........Rats End of lesson. Test to follow in November, 2012 Remember, November is to be set aside as rodent extermination month. |
Higher wattage for a resistor ever bad?
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". ;-) 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. |
Higher wattage for a resistor ever bad?
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." Jon |
Higher wattage for a resistor ever bad?
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. |
Higher wattage for a resistor ever bad?
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 |
Higher wattage for a resistor ever bad?
Don Lancaster wrote: 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. The burnt resistors were in series with zeners, one in a 30-year-old TV's remote control receiver board, the others (burnt and bulging) in a garage door opener containing 40xx series CMOS chips. I believe all of these resistors were run at close to their power ratings (garage door opener sat in 110-120F in summer). Also I had a CRT multisync monitor that burned out the output transistor in a large hybrid chip in its main power supply. It had a resistor connected to it that was definitely run above its power rating, but just briefly at turn-on, to help with a kick start circuit. It was only slightly discolored, and I was told to not replace it with anything larger because the low power rating may have been intended to provide protection. |
Higher wattage for a resistor ever bad?
On Thu, 18 Aug 2011 22:26:16 -0700, Jon Kirwan
wrote: 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. It certainly doesn't mean what's said is in all seriousness. Again, it shouldn't be surprising to anyone that you don't "get it". |
Higher wattage for a resistor ever bad?
On Fri, 19 Aug 2011 17:11:12 -0500, "
wrote: On Thu, 18 Aug 2011 22:26:16 -0700, Jon Kirwan wrote: 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. It certainly doesn't mean what's said is in all seriousness. Again, it shouldn't be surprising to anyone that you don't "get it". You just insist on being insulting, no matter what. Which shouldn't surprise anyone, either. Jon |
Higher wattage for a resistor ever bad?
On 08/16/2011 09:11 PM, larry moe 'n curly 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. A different sized resistor will have different characteristics at high frequency, so if those characteristics matter, there could be a problem. |
Higher wattage for a resistor ever bad?
On Fri, 19 Aug 2011 16:47:55 -0700, Jon Kirwan
wrote: On Fri, 19 Aug 2011 17:11:12 -0500, " wrote: On Thu, 18 Aug 2011 22:26:16 -0700, Jon Kirwan wrote: 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. It certainly doesn't mean what's said is in all seriousness. Again, it shouldn't be surprising to anyone that you don't "get it". You just insist on being insulting, no matter what. Which shouldn't surprise anyone, either. Sorry if the truth hurts but it is the truth. |
Higher wattage for a resistor ever bad?
On Fri, 19 Aug 2011 22:05:36 -0500, "
wrote: On Fri, 19 Aug 2011 16:47:55 -0700, Jon Kirwan wrote: On Fri, 19 Aug 2011 17:11:12 -0500, " wrote: On Thu, 18 Aug 2011 22:26:16 -0700, Jon Kirwan wrote: 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. It certainly doesn't mean what's said is in all seriousness. Again, it shouldn't be surprising to anyone that you don't "get it". You just insist on being insulting, no matter what. Which shouldn't surprise anyone, either. Sorry if the truth hurts but it is the truth. You insulted above without provocation. And then continue to repeat your error, again and again, without even being aware of just how that makes you look. I suppose that must be the painful truth you are talking about. You have my pity. Jon |
Higher wattage for a resistor ever bad?
On Aug 17, 3:41*am, "Martin Riddle" wrote:
"larry moe 'n curly" wrote in ... 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. No, it shouldn't be a problem. Different wattage is usually associated with size. If the resistor was 'cooked' then it was running at or beyond it's rating. Which means there was something else in the circuit that is defective. Most resistors are metal film nowadays, carbon comps are hard to come by. (But Carbon comps do handle peak currents much better than metal films.) Cheers fwiw most TH parts are carbon film Carbon comp, at least from the suppliers I use, are horribly expensive. Just due to the small market for them I guess, they certainly used to be the cheapest. NT |
Higher wattage for a resistor ever bad?
On Fri, 19 Aug 2011 22:12:59 -0700, Jon Kirwan
wrote: On Fri, 19 Aug 2011 22:05:36 -0500, " wrote: On Fri, 19 Aug 2011 16:47:55 -0700, Jon Kirwan wrote: On Fri, 19 Aug 2011 17:11:12 -0500, " wrote: On Thu, 18 Aug 2011 22:26:16 -0700, Jon Kirwan wrote: 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. It certainly doesn't mean what's said is in all seriousness. Again, it shouldn't be surprising to anyone that you don't "get it". You just insist on being insulting, no matter what. Which shouldn't surprise anyone, either. Sorry if the truth hurts but it is the truth. You insulted above without provocation. And then continue to repeat your error, again and again, without even being aware of just how that makes you look. The truth is not an insult. You rarely "get it". Lefties are like that. I suppose that must be the painful truth you are talking about. Is it painful? If so, seek help. It's certainly not painful to point out the truth. You have my pity. You really need to look in the mirror. |
Higher wattage for a resistor ever bad?
On Sat, 20 Aug 2011 12:28:22 -0500, "
wrote: On Fri, 19 Aug 2011 22:12:59 -0700, Jon Kirwan wrote: On Fri, 19 Aug 2011 22:05:36 -0500, " wrote: On Fri, 19 Aug 2011 16:47:55 -0700, Jon Kirwan wrote: On Fri, 19 Aug 2011 17:11:12 -0500, " wrote: On Thu, 18 Aug 2011 22:26:16 -0700, Jon Kirwan wrote: 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. It certainly doesn't mean what's said is in all seriousness. Again, it shouldn't be surprising to anyone that you don't "get it". You just insist on being insulting, no matter what. Which shouldn't surprise anyone, either. Sorry if the truth hurts but it is the truth. You insulted above without provocation. And then continue to repeat your error, again and again, without even being aware of just how that makes you look. The truth is not an insult. You rarely "get it". Lefties are like that. Still can't stop being insulting and not just to me. And you imagine this is _my_ problem. I have to love it. I suppose that must be the painful truth you are talking about. Is it painful? If so, seek help. It's certainly not painful to point out the truth. You gotta keep perseverating without end. I'm bored. You have my pity. You really need to look in the mirror. I'll leave you to suffer on at your war against whole groups you hate. I've see nothing new here to discuss so the thread is now yours. I'm bored. Jon |
Higher wattage for a resistor ever bad?
On Sat, 20 Aug 2011 02:51:54 -0700 (PDT), NT
wrote: On Aug 17, 3:41*am, "Martin Riddle" wrote: "larry moe 'n curly" wrote in ... 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. No, it shouldn't be a problem. Different wattage is usually associated with size. If the resistor was 'cooked' then it was running at or beyond it's rating. Which means there was something else in the circuit that is defective. Most resistors are metal film nowadays, carbon comps are hard to come by. (But Carbon comps do handle peak currents much better than metal films.) Cheers fwiw most TH parts are carbon film --- What do you mean by "TH"? -- JF |
Higher wattage for a resistor ever bad?
"John Fields" fwiw most TH parts are carbon film --- What do you mean by "TH"? ** Through Hole. Dear, oh dear ..... ..... Phil |
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