Current through coils
 

Thanks, Tom, for taking the trouble to go through the numbers. As I said
earlier, most of us know, and all engineers certainly should know,
superposition requires that results from an analysis using the total
current must be the same as the sum of the results from separate
analyses using forward and reflected currents (or any other components
whose sum is the total current). Your analysis shows this, as it should.

Roy Lewallen, W7EL

Current through coils
 

On Sat, 25 Mar 2006 17:43:08 +0000, Ian White GM3SEK
wrote:

First, several years ago, came the shocking observation that the
current into a coil is not the same as the current out of it. Somewhere
along the debate, this practical measurement was then expressed to be
in conflict with Kirchhoff's theories. ...

So much has been said in this debate - and this is at least the third or
fourth re-make of the whole show - that I honestly cannot remember if
the exact words that Richard reports were ever used.


Hi Ian (if you are still with us),

I stumbled upon the context in this snipe hunt:

On Sun, 05 Mar 2006 20:03:14 GMT, Cecil Moore wrote:

What would
Kirchhoff have thought about a coil with 0.1 amp
at the bottom and 0.7 amps at the top? It certainly
doesn't mean that 0.6 amps is flowing sideways.

To explain the application of "snipe hunt," this is a term suggesting
that someone is being set upon a fool's mission (an impossible goal
employing absurd tools). In the Navy is was catching sea bats, or
being on mail buoy watch.

73's
Richard Clark, KB7QHC

Current through coils
 

Richard Clark wrote:
On Sat, 25 Mar 2006 17:43:08 +0000, Ian White GM3SEK
wrote:

First, several years ago, came the shocking observation that the
current into a coil is not the same as the current out of it. Somewhere
along the debate, this practical measurement was then expressed to be
in conflict with Kirchhoff's theories. ...

So much has been said in this debate - and this is at least the third or
fourth re-make of the whole show - that I honestly cannot remember if
the exact words that Richard reports were ever used.


Hi Ian (if you are still with us),

Yeah, still here... and still wondering why...

I stumbled upon the context in this snipe hunt:

On Sun, 05 Mar 2006 20:03:14 GMT, Cecil Moore wrote:

What would
Kirchhoff have thought about a coil with 0.1 amp
at the bottom and 0.7 amps at the top? It certainly
doesn't mean that 0.6 amps is flowing sideways.

To explain the application of "snipe hunt," this is a term suggesting
that someone is being set upon a fool's mission (an impossible goal
employing absurd tools). In the Navy is was catching sea bats, or
being on mail buoy watch.

And here, it's about chasing single isolated comments.

Moral: don't hunt snipe unless you see a whole flock of 'em.


--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Current through coils
 

Richard Clark wrote:
I stumbled upon the context in this snipe hunt:

On Sun, 05 Mar 2006 20:03:14 GMT, Cecil Moore wrote:

What would
Kirchhoff have thought about a coil with 0.1 amp
at the bottom and 0.7 amps at the top? It certainly
doesn't mean that 0.6 amps is flowing sideways.

I think everyone here except Cecil knows where the current goes.

If Cecil admits to displacement currents, he has to also admit his
argument about reflected waves is incomplete.

73 Tom

Current through coils
 

If the lurkers think one can add or subtract the forward current
at both ends of the coils, as you did, I feel sorry for them.
--
73, Cecil http://www.qsl.net/w5dxp

I feel sorry for anyone who has to deal with you on a daily basis.

No wonder your wife split.

Current through coils
 

Roy Lewallen wrote:
Thanks, Tom, for taking the trouble to go through the numbers. As I said
earlier, most of us know, and all engineers certainly should know,
superposition requires that results from an analysis using the total
current must be the same as the sum of the results from separate
analyses using forward and reflected currents (or any other components
whose sum is the total current). Your analysis shows this, as it should.

Roy, would you please explain what is the technical significance
of Tom's superposing the forward wave of 1 amp at zero degrees at
the bottom of the coil with the forward wave of 1 amp at 45 degrees
at the top of the coil when those two currents are separated in
space by 12 inches and separated in time by 45 degrees of a cycle?

Doesn't the superposition principle require the two signals to exist
in the same space-time? The misconceptions being presented here are
unbelievable but apparently exist in the engineering community.
--
73, Cecil http://www.qsl.net/w5dxp

Current through coils
 

wrote:

Richard Clark wrote:

I stumbled upon the context in this snipe hunt:

Cecil Moore wrote:
What would
Kirchhoff have thought about a coil with 0.1 amp
at the bottom and 0.7 amps at the top? It certainly
doesn't mean that 0.6 amps is flowing sideways.

I think everyone here except Cecil knows where the current goes.

Those are standing wave currents, Tom. What is it about
func(kx)*func(wt) that you don't understand?

Take a look at the standing wave current distribution on a one
wavelength dipole at:

http://www.qsl.net/w5dxp/1WLDIP.GIF

The position in which a coil is installed in the standing wave
environment determines the magnitudes and phases of the currents
at the top and bottom of the coil. No magic displacement current
is required. If magic displacement current is not required in
a transmission line, why is it required in a coil? Hint: because
the lumped-circuit model is flawed.

If Cecil admits to displacement currents, he has to also admit his
argument about reflected waves is incomplete.

We can assume zero displacement current without much changing anything.
In the example at the top of this posting, there sure isn't 0.6 amps
of displacement current. I'm beginning to believe that you don't
understand superposition of forward and reflected waves. That would
explain a lot.

In the above example, the forward and reflected currents superpose to
0.7 amps at the top of the coil. That is simply closer to the standing
wave current maximum point. No displacement current required.

The forward and reflected currents superpose to 0.1 amp at the
bottom of the coil. That is simply closer to the standing wave
current minimum point. No displacement current required.

Exactly the same thing happens along a transmission line with
reflections. There's negligible displacement current between the
0.1 amp point and the 0.7 amp point on a transmission line. For
exactly the same reason, there can be negligible displacement
current in the coil. The forward current and reflected current
superpose in a coil just as they do in a transmission line.

If you would use the proper model and you will not need to resort
to any magic displacement current which is just a patch on a gaping
hole in the flawed lumped-circuit model.
--
73, Cecil http://www.qsl.net/w5dxp

Current through coils
 

wrote:

If the lurkers think one can add or subtract the forward current
at both ends of the coils, as you did, I feel sorry for them.

I feel sorry for anyone who has to deal with you on a daily basis.

The technical truth hurts, huh?

So Tom, please tell us the technical meaning of superposing two
currents separated in space by 12 inches and separated in time
by 45 degrees.
--
73, Cecil http://www.qsl.net/w5dxp

Current through coils
 

wrote:
I feel sorry for anyone who has to deal with you on a daily basis.

The distributed network model, with its superposition of forward
and reflected waves, explains everything without having to
resort to displacement currents.

The distributed network model is more powerful than the lumped
circuit model. The lumped circuit model is a subset of the
distributed network model.

When the two models agree, all is well. When the two models
disagree, the distributed network model is right and the
lumped circuit model is wrong.

You assume displacement currents exist because your model
requires them, not because they exist in reality. The distributed
network model illustrates just how unimportant displacement
currents really are. In the distributed network model, displacement
currents are often omitted as negligible.

In a high-Q coil, in a standing wave environment, radiation from
and losses in the coil are often negligible and can be ignored.
The large part of what happens to the standing wave current is
simply superposition of the forward and reflected waves. No
magic explanations required.

The delay through a real world 75m bugcatcher coil, predicted by
the distributed network model, is tens of degrees, not the faster
than light speed predicted by the lumped circuit model.
--
73, Cecil http://www.qsl.net/w5dxp

Current through coils
 

Cecil Moore wrote:
K7ITM wrote:

Cecil is unable (and believes it is
impossible) to determine the net charge in the volume containing the
coil as a function of time (to within a constant, at least), even
though the the wires in which we know the currents are the only way for
charge to get in and out of that volume.


THERE IS NO RF BATTERY STORING ENERGY! THERE IS ZERO LONG TERM
ACCUMULATION OF CHARGE! Neglecting losses, energy in exactly equals
energy out over the long term.

The fact that 2 amps of standing wave current exists at the bottom of
the coil and 1.4 amps of standing wave current exists at the top of
the coil doesn't imply any long term accumulation of charge. Long
term accumulation of charge in a coil is impossible.

Cecil,

I believe the long term average current is also zero. Therefore all of
these coils and antennas are totally inert. Problem solved.

It is a mystery why the discussion randomly switches from degrees of
phase and nanoseconds of time delay to long term averages, RMS, and
"net" something or other.

If you don't understand accumulation of charge in *every* AC and RF
circuit then there is little hope that you will ever get to an
understanding of the now-infamous "current through coil" problem.

73,
Gene
W4SZ