Who Has Used Resistors as Fuses

[[email protected]]

If you do it right, you can end up with a lot of current flowing at a
relatively low voltage drop with very little dissipation and no glow.

I would say that was doing it wrong.
What *I* think happens has nothing to do with carbon or metal film.
I think if you slowly heat some ceramics then the *wrong* ones will
become
good conductors.
This is very old knowledge indeed:
http://www.answers.com/topic/nernst-lamp?cat=technology

So your GreenPeace aspirant just selected an energy level that he
should
not have, heated up the ceramic rod, it became conductive, and voila
(=French for 'see' ) the situation you describe.
I did set out saying you need enough energy to 'evaporate' the stuff.

Now that makes sense.

 

[whit3rd]

Sometimes I burn too many regular fuses with prototypes.

Could I use a resistor ?
I was blowing 2amp fast blow pico fuses.

Yes, picofuses are pricey and a fusible resistor is cheaper
and works about the same. PTC is the fancy way to go, but
you can also use... a light bulb. A simple 200W@120V light
bulb will limit the current to 2A when your board shorts out,
and the cold resistance is relatively low (about 120 ohms)
so will permit normal operation at low currents.

It's a property of pure metals that they are ALL positive-tempco
resistors. Tungsten filaments included.

 

[[email protected]]

I would say that was doing it wrong.

What *I* think happens has nothing to do with carbon or metal film.
I think if you slowly heat some ceramics then the *wrong* ones will
become good conductors.

This is true, but irrelevant.

This is very old knowledge indeed:
http://www.answers.com/topic/nernst-lamp?cat=technology

So your GreenPeace aspirant just selected an energy level that he
should not have, heated up the ceramic rod, it became conductive, and voila
(=French for 'see' ) the situation you describe.

This is your theory, based on a thoroughly wrong-headed appreciation
of what was going on.

The body of the resistor I observed was not noticeably hot - certainly
not hot enough to conduct. The claim was that the current was being
carried through a hot channel in the carbon film. The core of the
channel was supposed to be very narrow, so it didn't take much power
dissipation to keep it hot enough to sustain almost metallic
conductivity. The resistor looked almost entirely normal after the
current was turned off.

I did set out saying you need enough energy to 'evaporate' the stuff.

And you were wrong.

Now that makes sense.

It might make sense to you, but it doesn't have anything to do with
what I observed.

 

[Jan Panteltje]

It might make sense to you, but it doesn't have anything to do with
what I observed.

Observation is very subjective.
I am sure you have some reference with measurements?

I was thinking this way:
1) manufacturer name: MuchProfit
2) Designer name: NoKnowledge

MuchProfit:
For a 1/4 W 4.7 Ohm resistor the max voltage will be U^2 / 4.7 = 1/4 say 1V.
For a 1% error the ceramic resistance at max temp can be 4700 Ohm, I will
use cheapest ceramic from (China?).

NoKnowledge:
I will use this 4.7 Ohm as fusible in a 325V DC circuit after the rectifier,
it will limit surge too, it will carry about 210 mA, so drop about a volt,
Within resistor power rating.

Event:
Some time on, resistor temp 150 degrees C, a short happens, resistor carbon
coating evaporates, now we have 300 V in 4700 Ohm = 90000 / 4700 W = 19 W
dissipated in the ceramic, it get hotter fast, starts to glow, room lights up,
resistance gets lower, more light

A NEW STAR IS BORN.


Sorry, could not resist.

<disclaimer>
Al persons are purely real, all theory need not be>
<end disclaimer>

<claimer>
I wrote this.
< end claimer>

<small print>
..
<end small print>

 

[[email protected]]

Observation is very subjective.
I am sure you have some reference with measurements?

Don't be silly. This was some thirty years ago. But observation isn't
all that subjective.

The object of the demonstration was to make a point, and the point was
made clearly enough that I remember it still - carbon film resistors
can't be relied on to fail open circuit, and can (under appropriate
circumstances) fail to a state that looks very like a short circuit.

I was thinking this way:

Don't flatter yourself.

<snipped comedy>

 

[Jan Panteltje]

Don't be silly. This was some thirty years ago. But observation isn't
all that subjective.

mmm, keep dreaming ;-)

 

[Palinurus]

Sometimes I burn too many regular fuses with prototypes.

Could I use a resistor as a temporary fuse substitute?
It's ok if the fuse bursts into flames..
Affer debugging, I'll used a proper fuse.

Has anybody sacrificed resistors like this?
If so, which resistor type makes for a good fuse?
Carbon? Thick film? Thin film? Wirewound?

I was blowing 2amp fast blow pico fuses.
D from BC

-
The only place where I've seen this done in a production device was on
a Newport panel meter. It was a 10 ohm 1/10 watt carbon composition
resistor. Never saw one blow, but from the aftereffects, it was pretty
violent. Apparently, it worked. I've never done it myself, since I've
never blown more than one or two fuses in all the things I've built, and
at a buck or two each, it was no big deal.
In this vein, I'd like to add that from painful experience I distrust
polyswitches and all their relatives. They're slow, have a limited life,
can fail destructively or in an irritating half-on manner, and have a
narrow range of application. It's an interesting idea, but they are by
no means to be considered a general replacement for fuses. This was one
of those all too rare instances where I was able to learn from others'
mistakes, rather than my own.

 

[D from BC]

-
The only place where I've seen this done in a production device was on
a Newport panel meter. It was a 10 ohm 1/10 watt carbon composition
resistor. Never saw one blow, but from the aftereffects, it was pretty
violent. Apparently, it worked. I've never done it myself, since I've
never blown more than one or two fuses in all the things I've built, and
at a buck or two each, it was no big deal.
In this vein, I'd like to add that from painful experience I distrust
polyswitches and all their relatives. They're slow, have a limited life,
can fail destructively or in an irritating half-on manner, and have a
narrow range of application. It's an interesting idea, but they are by
no means to be considered a general replacement for fuses. This was one
of those all too rare instances where I was able to learn from others'
mistakes, rather than my own.

I don't know much about polyswitches.
I think it only works as fast as it's temperature rate of rise.
A chunk of polyswitch material doesn't instantly heat up..
D from BC

 

[[email protected]]

mmm, keep dreaming ;-)

Unfortunately your confident assertion that carbon resistors always
blow open circuit is the dream. Enjoy it while it lasts.

 

[Jan Panteltje]

Unfortunately your confident assertion that carbon resistors always
blow open circuit is the dream. Enjoy it while it lasts.

Your reading disability is such that you missed out on a whole lot of conditions,
perhaps you were sleep reading.
RINGGGGGGGGGGGGGGGGGGGGGGGGGGGG

 

[[email protected]]

Your reading disability is such that you missed out on a whole lot of conditions,
perhaps you were sleep reading.
RINGGGGGGGGGGGGGGGGGGGGGGGGGGGG

Dream on. Reality has a tendency to ignore engineer-imposed
conditions.

 

[Jan Panteltje]

Dream on. Reality has a tendency to ignore engineer-imposed
conditions.

Dear Bill, I do not want to get into a fight about this.
Of course you are 100% right that reality may ignore your conditions.
But I realized only late last nigh, - just before falling asleep - the greatness
of the event you witnessed 30 years ago.
It hit me (like a ton of bricks) that you witnessed the 'body temperature carbon superconductor'.
Now that is good for a free ticket to a northern country to receive the Nobel.

May I humbly suggest you cross-post your carbon experience to sci.physics, as
many people there are desperately looking for just such a thing, and will be more then happy
to nominate you, or even claim they were first.
Some other great names of observers come to light : Pons & Fleischman for example,
who also observed Nobel stuff and are still working very hard to reproduce it.

What will you do with all that prize money?

 

[[email protected]]

Dear Bill, I do not want to get into a fight about this.

After three remarkably skeptical postings from you, this comes as a
surprise.

Of course you are 100% right that reality may ignore your conditions.

My reading must be disabled - I though you were referring to
conditions that you had specified.

But I realized only late last nigh, - just before falling asleep - the greatness
of the event you witnessed 30 years ago.
It hit me (like a ton of bricks) that you witnessed the 'body temperature carbon superconductor'.
Now that is good for a free ticket to a northern country to receive the Nobel.

There was a voltage drop, and some heat dissipation so it wasn't
superconductivity. Like I said, the current seems to have concentrated
itself into a narrow channel, in which the carbon was very hot, with a
correspondingly low (but non-zero) resistance.

May I humbly suggest you cross-post your carbon experience to sci.physics, as
many people there are desperately looking for just such a thing, and will be more then happy
to nominate you, or even claim they were first.

Since the target audience could expected to read my account more
carefully than you have, they would immediately detect that the event
did not involve superconductivity.

Some other great names of observers come to light : Pons & Fleischman for example,
who also observed Nobel stuff and are still working very hard to reproduce it.

When I was a post-doc in Southampton, from 1971 to 1973, I met
Fleischman - he was professor of electrochemistry there at that time.
I can't remember a thing about him ... I don't think it would be all
that hard to reproduce the effect that I saw. I've got Colin hunter's
address somewhere, and he could probably tell me how he managed to set
up the hot channel in the carbon film - he'd got one of the
apprentices to spend a couple days working out out how to initiate the
channelling reliably before he went to trouble of dragging the
engineers around to see the hot channel in action.

What will you do with all that prize money?

I'll save worrying about that until there is a chance that I might win
it.

 

[Don Lancaster]

After three remarkably skeptical postings from you, this comes as a
surprise.




My reading must be disabled - I though you were referring to
conditions that you had specified.




There was a voltage drop, and some heat dissipation so it wasn't
superconductivity. Like I said, the current seems to have concentrated
itself into a narrow channel, in which the carbon was very hot, with a
correspondingly low (but non-zero) resistance.




Since the target audience could expected to read my account more
carefully than you have, they would immediately detect that the event
did not involve superconductivity.




When I was a post-doc in Southampton, from 1971 to 1973, I met
Fleischman - he was professor of electrochemistry there at that time.
I can't remember a thing about him ... I don't think it would be all
that hard to reproduce the effect that I saw. I've got Colin hunter's
address somewhere, and he could probably tell me how he managed to set
up the hot channel in the carbon film - he'd got one of the
apprentices to spend a couple days working out out how to initiate the
channelling reliably before he went to trouble of dragging the
engineers around to see the hot channel in action.




I'll save worrying about that until there is a chance that I might win
it.

A ten megohm resistor makes an ideal fuse as you will never have to
replace it.



--
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: [email protected]

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

 

[[email protected]]

A ten megohm resistor makes an ideal fuse as you will never have to
replace it.

Unless your equipment happens to be somewhere close to a lightning
strike. Given a sufficiently high voltage difference across the
resistor, it is possible to destroy even a 10M part.

Let me tell you about 100kV scanning electron microscopes and Nijmegen
University's system for making very high transient magnetic fields ...

 

[neon]

why try to burn things up before finding the proplem . a solder jumper is better then a resistor quick too a resistor must exceed max power to burn. but it is silly to try it because your trouble whatever will not go away by wishfullthinking.