Stupid question of the day....

[TokaMundo]

On Sun, 07 Aug 2005 18:59:43 -0500, John Fields
<jfields@austininstruments.com> Gave us:

Yeah, I still do... It's _my_ lab.

Same question you refused to answer last time. When was the last
time you used a soldering iron?

 

[TokaMundo]

On Sun, 07 Aug 2005 20:00:19 -0500, John Fields
<jfields@austininstruments.com> Gave us:

On Sun, 07 Aug 2005 22:43:51 GMT, TokaMundo
TokaMundo@weedizgood.org> wrote:

On Sun, 07 Aug 2005 17:29:17 -0500, John Fields
jfields@austininstruments.com> Gave us:

Not at all. From every indication, so far, it seems you _can_
accept a modicum of instruction, but then you plateau out.

Get it through your head, you retarded fuck. I don't need your
assessments.

---
What you mean is that you don't _want_ my assessments but, dumbass,
you can't always get what you want.

But if you try sometime, you just might find, you get what you need.

Look, retard boy. I don't need some asswipe that can't even make
posts to Usenet correctly (without posting blank messages all the
fucking time) telling me what my errors are. Deal with your own.

You should take that last line to heart. You know... heart
attack... or maybe it means something else...

 

[John Fields]

On Mon, 08 Aug 2005 19:46:49 GMT, TokaMundo
<TokaMundo@weedizgood.org> wrote:

On Sun, 07 Aug 2005 19:48:44 -0400, keith <krw@att.bizzzz> Gave us:

On Sun, 07 Aug 2005 22:43:51 +0000, TokaMundo wrote:

On Sun, 07 Aug 2005 17:29:17 -0500, John Fields
jfields@austininstruments.com> Gave us:

Not at all. From every indication, so far, it seems you _can_
accept a modicum of instruction, but then you plateau out.

Get it through your head, you retarded fuck. I don't need your
assessments.

Perhaps you don't _need_ them to survive on the plnet, but you would do
well to listen. Of course you know-it-all, so why would you "listen",
even to your superiors.

You're an idiot. You also made a spelling error, yet yours won't be
highlighted by the troll ASS. Starting to see a pattern, dipshit?

---
I am. You were an asshole yesterday, you're an asshole today, and
you'll be an asshole tomorrow.
---

You fucking correct all retards are real funny to watch spin in
little convoluted circles.

---
That really _should_ be "correct-all"

--
John Fields
Professional Circuit Designer

 

[John Fields]

On Mon, 08 Aug 2005 19:48:03 GMT, TokaMundo
<TokaMundo@weedizgood.org> wrote:

On Sun, 07 Aug 2005 18:59:43 -0500, John Fields
jfields@austininstruments.com> Gave us:

Yeah, I still do... It's _my_ lab.

Same question you refused to answer last time. When was the last
time you used a soldering iron?

---
Refused to answer???

About ten minutes ago, why?

--
John Fields
Professional Circuit Designer

 

[John Fields]

On Mon, 08 Aug 2005 19:50:16 GMT, TokaMundo
<TokaMundo@weedizgood.org> wrote:

Look, retard boy. I don't need some asswipe that can't even make
posts to Usenet correctly (without posting blank messages all the
fucking time) telling me what my errors are. Deal with your own.

---
Tough shit, asshole, that's what you're gonna get.
You want it to stop? Stop making misteaks.
---

You should take that last line to heart. You know... heart
attack... or maybe it means something else...

---
"Deal with your own"? What does that have to do with anything?

--
John Fields
Professional Circuit Designer

 

[John Larkin]

On Sun, 07 Aug 2005 22:15:39 GMT, "daestrom"
<daestrom@NO_SPAM_HEREtwcny.rr.com> wrote:

A spiral of #10 bare copper wire in a plastic garbage can full of
water makes an impressive dummy load, up until the water gets hot
enough to melt the plastic can. Then the hot water gets loose. Keep a
good chair handy.


So your plastic garbage can melts at 212F, or you let the wire touch the
can?

Neither. But if you fill a typical plastic garbage can with boiling
water, expect to be knee-deep in it pretty soon. Trust me on this one.

John

 

[Don Bowey]

On 8/8/05 2:03 PM, in article 9thff1tb8474cdsnpg61kobiuloc7988ah@4ax.com,
"John Fields" <jfields@austininstruments.com> wrote:

On Mon, 08 Aug 2005 19:50:16 GMT, TokaMundo
TokaMundo@weedizgood.org> wrote:


Look, retard boy. I don't need some asswipe that can't even make
posts to Usenet correctly (without posting blank messages all the
fucking time) telling me what my errors are. Deal with your own.

---
Tough shit, asshole, that's what you're gonna get.
You want it to stop? Stop making misteaks.
---

You should take that last line to heart. You know... heart
attack... or maybe it means something else...

---
"Deal with your own"? What does that have to do with anything?

Whichever of you just quits posting to this ridiculous thread, is sure a lot
brighter bulb than the other.

 

[John Fields]

On Mon, 08 Aug 2005 14:57:16 -0700, Don Bowey <dbowey@comcast.net>
wrote:

Whichever of you just quits posting to this ridiculous thread, is sure a lot
brighter bulb than the other.

---
You're right, and I'm done.

--
John Fields
Professional Circuit Designer

 

[daestrom]

"TokaMundo" <TokaMundo@weedizgood.org> wrote in message
news:gh2df1d5s6vqn6qq4fbubkciqg53p01jgm@4ax.com...

On Sun, 07 Aug 2005 22:15:39 GMT, "daestrom"
daestrom@NO_SPAM_HEREtwcny.rr.com> Gave us:

But this discussion forced me to 'sharpen the pencil' and do the actual
calculus. Turns out it is a pretty small effect in most practical
conductors (but not 'Toka's zero).

I believe I said "near zero", Daystruck. I also believe that my
analogies were and are closer to the truth than the curve you
declared.

What you 'believe' you said, and what is in the archive are two different
things. Deal with it.

daestrom

 

[Bob Myers]

"John Fields" <jfields@austininstruments.com> wrote in message
news:c1gff1le76mkog4u4e5kc95meapgjgvu6e@4ax.com...

I am. You were an asshole yesterday, you're an asshole today, and
you'll be an asshole tomorrow.

But you DO have to admire consistency like that...

Bob M.

 

[daestrom]

"TokaMundo" <TokaMundo@weedizgood.org> wrote in message
news:0m2df11rbuc8l2ubg5coqq5g2sbs0nbir1@4ax.com...

On Sun, 07 Aug 2005 22:15:39 GMT, "daestrom"
daestrom@NO_SPAM_HEREtwcny.rr.com> Gave us:


Yeah, especially when solid 'phase-changes' take place. Some steels
undergo
some interesting crystaline changes from 'body-centered cubic' to
'face-centered' at high temperatures and actually absorb a far amount of
heat doing it with no appreciable temperature rise. So I can imagine such
'shifts' in thermal conductivity can occur.

That's why welding works the way it does, and soldering works the
way it does.

No silly. What I'm talking about is not a phase change from solid to liquid
(soldering and welding are examples of that).

Steel and many other alloys undergo 'phase changes' from one form of solid
to another form of solid. The crystaline structure shifts from one form to
another *without* becoming a liquid. Looking at a bar of low-carbon steel
in a furnace before/after such phase changes, you cannot see any difference.
Sudden cooling back down below the transition temperature ('quenching') can
trap the crystaline structure in the high-temperature state, providing
useful properties (look up 'hardening'). Alternatively, it may be heated
well above the transition, then cooled very slowly to remove brittleness
('annealing').

Materials like this have very marked changes in thermal conductivity at
these transition temperatures and often absorb/liberate a fair amount of
heat with no significant temperature change while this crystaline change
occurs.

daestrom

 

[daestrom]

"TokaMundo" <TokaMundo@weedizgood.org> wrote in message
news:a82df19mt0boio5f1uc67vpev60h83l6g2@4ax.com...

On Sun, 07 Aug 2005 12:05:21 -0700, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> Gave us:

On Sun, 07 Aug 2005 16:10:37 GMT, "daestrom"
daestrom@NO_SPAM_HEREtwcny.rr.com> wrote:


"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in
message
news:6d08f1d39hgu458cpg4cjchqgr91ln1l12@4ax.com...
On Fri, 05 Aug 2005 21:17:47 GMT, "daestrom"
daestrom@NO_SPAM_HEREtwcny.rr.com> wrote:

snip


Well I *almost* agree with you. To get a severe gradient, you do need
to
run a lot of current. But it still does *NOT* matter what is in
contact
with the outside surface.

Sure it does. If you run a copper wire in air, and dump in enough
current to produce a decent radial gradient, it will vaporize. You'd
have to water cool it (boiling water is ideal) to sustain the power
levels necessary for a non-trivial gradient.

Copper conducts heat about 12,000 times as well as air, and there's a
lot more air available than copper in most situations. So, very
roughly, a 1mm copper wire surrounded by a 10 mm air gap, with enough
current flowing to create a 1 deg C internal gradient, will have a
surface temp of 120,000 C.



Nah... The thermal conductivity of a film coefficient for air is not the
same as the thermal conductivity of air. The thermal conductivity is
only
relavent in a very thin layer against the surface (much less than 10 mm).
Moving outward, the viscosity and velocity of the air become dominant.
Given the film coefficient of air against a vertical surface of about 25
W/(m^2-K), I make it out to only be about 8,000 C. ;-) Having forced air
convection (or a good 'stiff' wind) can improve the film coefficient to
almost 200 W/(m^2-K) (down to 1,000 C ;-). Water cooling can be as high
as
5000 to 10000 W/(m^2-K) (as low as 20 C).



I did hedge my number with "very roughly", figuring I could be 2
orders of magnitude off and still make the point.


But larger wires, and those of Al can develop such a gradient more
easily.
And true, boiling heat transfer can be several orders of magnitude
better,
but one then has to worry about exceeding the critical heat flux (also
known
as 'departure from nucleat boiling', 'boiling transition', or 'dryout').
Whether the water is circulating or not, and how far the bulk water
temperature is from saturation also become important (i.e. becomes a real
engineering nightmare).

A spiral of #10 bare copper wire in a plastic garbage can full of
water makes an impressive dummy load, up until the water gets hot
enough to melt the plastic can. Then the hot water gets loose. Keep a
good chair handy.


The industry has a long history of success using pressurized hydrogen.
Most
large generators and their connections to step-up transformers are cooled
this way. Much better cooling than plain air, allowing much higher
current
densities. And with the same material properties, stronger temperature
gradients.

Except all of the H2-cooled gen-xfmr leads that I've seen use hollow
conductors with H2 forced through the center as well as surrounding the
outside. Similarly, the water-cooled conductors that I've seen are those
found in generators and the water flows down the center of the hollow
conductor. Not much of a temperature profile when the cross-section is
mostly cooling water ;-)

The internal gradient is a function of the heat
generated per unit mass and the thermal conductivity of the material.
Period. Nothing else.


Not once it's gaseous.

True, but one usually designs to avoid melting, much less boiling.

Fact is, in 60hz applications, the usual design restrictions regarding
skin-effect overshadow any problems with centerline temperature concerns.
Perhaps engineers working with high-current DC applications are more
concerned with the temperature gradient issues. But I suspect it is
still
small for good thermal conductors like copper.

I jumped into this fray when 'TokaMundo' said, "In a wire,....would show
the
wire at the same temp from center to outer surface". I think we agree
this
is wrong. And I agree that the temperature gradient is not severe for
conductors made of Cu or Al under normal circumstance such as air
cooling.
But *some* gradient *must* exist, otherwise the centerline temperature
must
increase (due to heat generated and not conducted away) until a gradient
begins to conduct heat away as fast as it's created by the electric
current.

Wonder how bad it is for graphite rods used in electric furnaces? Of
course
graphite has a much higher melting temperature so it can withstand a
strong
gradient. But graphite, with its lower thermal conductivity and higher
resistivity, probably develops a very strong gradient. Coupled with the
temperature coefficient of resistivity, it might make for an interesting
current distribution. Even for DC applications.


The external medium will determine the exact temperature of the outer
surface, and by virtue of the gradient for the specific material/power,
the
centerline temperature. But the shape and relative height of the
gradient
is irrespective of the external surface (as long as the thermal
conductivity
and heat produced are assumed constant).

Thermal conductivity is itself a function of temperature, so the
gradient does depend mildly on the absolute temperature of the whole
rig. Especially after the copper melts.


True. But below the melting point, it isn't hard to approximate the
variance with a low-order polynomial using temperature alone as the
independent variable. I would think this would make it relatively easy
to
incorporate into the integration. Haven't tried it though, so who
knows???

daestrom



My conclusion from this thread is that skin effect can be important at
60 Hz in entirely practical situations, and thermal gradients in
copper or aluminum conductors are inconsequential unless the current
is high and the cooling novel. We're doing some thermocouple stuff
just now (a simulator module and a complementary measurement gadget,
for jet engine testing) so thermal stuff is on my mind.

I've done a little superconductive/cryo work, where things are very
different. Here, the thermal conductivity of metals changes radically
as a function of temperature, so the net heat flow of, say, a
stainless or manganin leadwire from 4K up to to room temp is
determined by a complex integral (the bottom line of which,
fortunately, you can just look up.)

Yeah, the Toka guy is weird. He insists on crudely insulting anyone
who disagrees with him, and he's usually wrong. Some people seek and
need public humiliation: Usenet pain sluts, as it were.


That's funny since your position supports what I said about the
gradient being negligible, not the full on slope that daystruck
equates.

Here, does this look familiar???
8/4/2005 1:24 AM TokaMundo wrote....

In the wire, since the heat is generated throughout the medium via
current flow, even from low currents on up to my cherry red scenario
would show the wire at the same temp from center to outer surface.

You claim that because the 'heat is generated throughout the medium...' the
wire would be at the *same* temperature from center to outer surface??
That's just plain wrong, and you're the one that said it.

Further down in the same post you also said...

The "thermal skin" of the wire that would be slightly cooler due to
surface convection is very thin and beneath it the medium has even
temperature, not a gradient to the center.

The temperature gradient is *not* limited to some imaginary 'very thin'
"thermal skin" as you tried to say here. Again you're just plain wrong.

And as far as what *I* said, on 8/2/2005 6:01PM

So the *temperature* profile throughout the conductor is far from 'even'.
If the material has a positive temperature coefficient of resistivity (as
do
both copper and Al), then the resistence of the central core is higher than
the outer surface. The exact amount of temperature difference is a
function
of the electrical resistivity and thermal conductance of the material.

And later to John Larkin I replied...

Well I *almost* agree with you. To get a severe gradient, you do need to
run a lot of current. But it still does *NOT* matter what is in contact
with the outside surface. The internal gradient is a function of the heat
generated per unit mass and the thermal conductivity of the material.
Period. Nothing else.

I haven't said any where that there is a 'full on slope' (whatever that's
supposed to mean).

Having a little trouble admitting your mistakes are you??

daestrom

 

[TokaMundo]

On Mon, 08 Aug 2005 15:58:06 -0500, John Fields
<jfields@austininstruments.com> Gave us:

On Mon, 08 Aug 2005 19:48:03 GMT, TokaMundo
TokaMundo@weedizgood.org> wrote:

On Sun, 07 Aug 2005 18:59:43 -0500, John Fields
jfields@austininstruments.com> Gave us:

Yeah, I still do... It's _my_ lab.

Same question you refused to answer last time. When was the last
time you used a soldering iron?

---
Refused to answer???

About ten minutes ago, why?

I doubt it.

 

[TokaMundo]

On Mon, 08 Aug 2005 23:07:43 GMT, "daestrom"
<daestrom@NO_SPAM_HEREtwcny.rr.com> Gave us:

"TokaMundo" <TokaMundo@weedizgood.org> wrote in message
news:gh2df1d5s6vqn6qq4fbubkciqg53p01jgm@4ax.com...
On Sun, 07 Aug 2005 22:15:39 GMT, "daestrom"
daestrom@NO_SPAM_HEREtwcny.rr.com> Gave us:

But this discussion forced me to 'sharpen the pencil' and do the actual
calculus. Turns out it is a pretty small effect in most practical
conductors (but not 'Toka's zero).

I believe I said "near zero", Daystruck. I also believe that my
analogies were and are closer to the truth than the curve you
declared.


What you 'believe' you said, and what is in the archive are two different
things. Deal with it.

You're an idiot. You got shown to be way off. You deal with it.

 

[TokaMundo]

On Mon, 08 Aug 2005 23:19:08 GMT, "daestrom"
<daestrom@NO_SPAM_HEREtwcny.rr.com> Gave us:

No silly. What I'm talking about is not a phase change from solid to liquid
(soldering and welding are examples of that).

I wasn't talking about that. I was talking about the differences in
the way the heat that is generated in each of those systems travels in
the mediums local to the work being done.

In soldering, only surface interfaces are typically made The items
being joined do not meld into the joints themselves, and the heat is
local to the joining but soaked in the nearby local medium before and
during the solder joint making. The joining media is usually
different than the mediums joined.

In welding, the surfaces being joined are actually melted and
considerable additional like material is introduced. The finished
joint consists of parts of both joined mediums and the added media
becoming part of the joint at depths that are near half the thickness
of the joined parts.

The types of heat transfers that were being discussed closely
reflect the way welded steel works. Silly.

 

[TokaMundo]

On Mon, 08 Aug 2005 23:19:08 GMT, "daestrom"
<daestrom@NO_SPAM_HEREtwcny.rr.com> Gave us:

(look up 'hardening')

I don't need to look up hardening.

I used to build chillers. That goes beyond hardening.

Look it up.

 

[John Gilmer]

The bundling of conductors (say 2 to 4 conductors spaced 30-45cm apart) is
an extension of this - effective very large diameter and lower surface
fields and series inductance at a reasonable price and weight savings.
This
has nothing to do with skin effect.

But it does!

At 60 Hz, the "skin effect" caused most of the current to flow within 1/2"
of the surface. That's why conductors over 1" or so either have steel for
strength or might have a light weight filler since a solid conduction would
add to the weight but not to the electrical performance.

Beyond a certain current capacity, it makes sense to have several conductors
that aer a little over 1" in diameter than a single conductor that is sized
as needed. There are likely other considerations too: the separate
conductors would have more area and would be more effectively cooled by the
air in the line is really being pushed.


> --

 

[TokaMundo]

On Tue, 9 Aug 2005 08:54:56 -0400, "John Gilmer"
<gilmer@crosslink.net> Gave us:

The bundling of conductors (say 2 to 4 conductors spaced 30-45cm apart) is
an extension of this - effective very large diameter and lower surface
fields and series inductance at a reasonable price and weight savings.
This
has nothing to do with skin effect.

But it does!

At 60 Hz, the "skin effect" caused most of the current to flow within 1/2"
of the surface. That's why conductors over 1" or so either have steel for
strength or might have a light weight filler since a solid conduction would
add to the weight but not to the electrical performance.

Beyond a certain current capacity, it makes sense to have several conductors
that aer a little over 1" in diameter than a single conductor that is sized
as needed. There are likely other considerations too: the separate
conductors would have more area and would be more effectively cooled by the
air in the line is really being pushed.

Multiple segregated conductors is how Litz wire works. The
effective surface area or "skin" if you will, is greater. On low
frequency, high tension lines, it is handled by four or five
physically separated larger than 1" diameter lines. They may or may
not be electrically segregated along their length.

In a high frequency switcher transformer, it is multiple strands of
mag wire separated by their enamel, and connected only on their ends.
The Litz bundle can carry more current than a solid wire in such cases
as it will drop less voltage at higher frequencies.

Both cases yields more cross sectional area for conduction through
the line.

 

[Paul Hovnanian P.E.]

John Fields wrote:

On Sat, 30 Jul 2005 15:14:37 GMT, "JoeSixPack" <olegp@telus.net
wrote:

Before you attack this post, saying electrons can only travel at the speed
of light, that's incorrect. The electrons themselves can travel any speed,

---
No, they can only travel at speeds less than the speed of light.
---

but the voltage wave produced does travel at 300,000 kms per second.

---
It's not a "voltage" wave, it's an electromagnetic wave, and it can
only propagate at the speed of light in a vacuum.

Either an Electrolux or a Hoover.

;-)

--
Paul Hovnanian mailtoaul@Hovnanian.com
------------------------------------------------------------------
APL is a write-only language. I can write programs in APL, but I
can't read any of them.
-- Roy Keir

 

[DBLEXPOSURE]

"Paul Hovnanian P.E." <Paul@Hovnanian.com> wrote in message
news:42F97A5A.9D3C5AE7@Hovnanian.com...

John Fields wrote:

On Sat, 30 Jul 2005 15:14:37 GMT, "JoeSixPack" <olegp@telus.net
wrote:

Before you attack this post, saying electrons can only travel at the
speed
of light, that's incorrect. The electrons themselves can travel any
speed,

---
No, they can only travel at speeds less than the speed of light.
---

but the voltage wave produced does travel at 300,000 kms per second.

---
It's not a "voltage" wave, it's an electromagnetic wave, and it can
only propagate at the speed of light in a vacuum.

Either an Electrolux or a Hoover.

;-)

--
Paul Hovnanian mailtoaul@Hovnanian.com
------------------------------------------------------------------
APL is a write-only language. I can write programs in APL, but I
can't read any of them.
-- Roy Keir

Hey, My Dirt Devil, 2C

The house clean before it ever gets dirty....

;^)