Higher wattage for a resistor ever bad?
larry moe 'n curly
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.
John Tserkezis
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.
Jon Kirwan
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
Rich Grise
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
Lord Valve
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
Martin Riddle
"larry moe 'n curly" <larrymo...@my-deja.com> wrote in message
news:4765c808-4b10-438c...@cf8g2000vbb.googlegroups.com...
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
upsid...@downunder.com
A larger resistor may have different stray inductances and
capacitances, which might affect some RF circuits.
Phil Allison
"larry moe 'n curly"
** 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
John Fields
<marti...@verizon.net> wrote:
>
>
>"larry moe 'n curly" <larrymo...@my-deja.com> wrote in message
>news:4765c808-4b10-438c...@cf8g2000vbb.googlegroups.com...
>> 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/showpage.cgi?product=little_demon
http://www.seielect.com/Catalog/SEI-rc.pdf
http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=66690
--
JF
Bill Sloman
> "larry moe 'n curly" <larrymoencu...@my-deja.com> wrote in messagenews:4765c808-4b10-438c...@cf8g2000vbb.googlegroups.com...
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
Spehro Pefhany
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"
sp...@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
Lord Valve
> 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
Spehro Pefhany
"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.
Don Lancaster
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: d...@tinaja.com
Please visit my GURU's LAIR web site at http://www.tinaja.com
Jon Kirwan
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
Spehro Pefhany
<jo...@infinitefactors.org> 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.
John Fields
<spef...@interlogDOTyou.knowwhat> wrote:
>On Wed, 17 Aug 2011 13:34:16 -0700, the renowned Jon Kirwan
><jo...@infinitefactors.org> 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
Tim Wescott
> On Wed, 17 Aug 2011 13:34:16 -0700, the renowned Jon Kirwan
> <jo...@infinitefactors.org> 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.
George Herold
wrote:
> On Wed, 17 Aug 2011 13:34:16 -0700, the renowned Jon Kirwan
>
>
> >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.
Jon Kirwan
>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
Ron D.
Got any penneys to replace a blown fuse?
isw
"Phil Allison" <phi...@tpg.com.au> wrote:
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
Wild_Bill
is that a hearse of a different color?
--
Cheers,
WB
.............
"Lord Valve" <detr...@ix.netcom.com> wrote in message
news:4E4B2915...@ix.netcom.com...
JW
Message id: <9b241m...@mid.individual.net>:
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.
Michael A. Terrell
"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.
k...@att.bizzzzzzzzzzzz
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.
Jon Kirwan
><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
k...@att.bizzzzzzzzzzzz
wrote:
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.
Jon Kirwan
<k...@att.bizzzzzzzzzzzz> wrote:
One can never be sure what a smiley means. And I'm kind of
proud of being literal-minded, anyway.
Jon
larry moe 'n curly
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.
k...@att.bizzzzzzzzzzzz
wrote:
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".
Jon Kirwan
<k...@att.bizzzzzzzzzzzz> wrote:
You just insist on being insulting, no matter what. Which
shouldn't surprise anyone, either.
Jon
cjt
> 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.
k...@att.bizzzzzzzzzzzz
wrote:
Sorry if the truth hurts but it is the truth.
Jon Kirwan
<k...@att.bizzzzzzzzzzzz> wrote:
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
NT
> "larry moe 'n curly" <larrymoencu...@my-deja.com> wrote in messagenews:4765c808-4b10-438c...@cf8g2000vbb.googlegroups.com...
>
> > 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.
>
> 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.
>
> 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
k...@att.bizzzzzzzzzzzz
wrote:
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.
Jon Kirwan
<k...@att.bizzzzzzzzzzzz> wrote:
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
John Fields
wrote:
>On Aug 17, 3:41 am, "Martin Riddle" <martin_...@verizon.net> wrote:
>> "larry moe 'n curly" <larrymoencu...@my-deja.com> wrote in messagenews:4765c808-4b10-438c...@cf8g2000vbb.googlegroups.com...
>>
>> > 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
Phil Allison
"John Fields"
>>
>>fwiw most TH parts are carbon film
>
> ---
> What do you mean by "TH"?
** Through Hole.
Dear, oh dear .....
.... Phil
Teodor Väänänen
And from what I've understood, there isn't a clear standard as to how
metal films are marked as opposed to carbon films, so you would have to
know what resistor manufacturer the equipment manufacturer used in order
to be able to tell what type is in the device.
You can deduce some from the application as well as tolerance, but it's
by no means a sure-fire way.
Just my $.02 worth,
/Teo.
--
Teodor Väänänen | Don't meddle in the affairs of wizards,
teostup...@algonet.se | for you are good and crunchy with
Remove stupidity to reply | ketchup.