On 5/18/12 11:20 PM, Bart B. Anderson wrote:
On 5/16/2012 4:36 AM, Jim Lux wrote:
Heating depends on I^2R losses over time and
the heat that will occur on the primary at that inner turn or two if
very different for SG compared to SS. We can attempt rms numbers in the
primary, but if your gonna do that, don't leave out proximity effects
that occur from circulation currents from turn to turn and whatever
else.
I don't know that there's any extra current turn to turn, but there
probably is an uneven current distribution "around" the tube.
There are proximity losses of course and basic losses through the main
impedance of the primary. The can be all significant. For little coils
running basic NST's and what not, no, it's of no concern. It's always a
power thing.
What is the proximity loss? I would think that the current is the same
in the inductor AND that the AC resistance doesn't change. Yes, the
current is squeezed away from adjacent turns, but the effect on turn 2
(counting from the inside) and turn 8 should be the same (with constant
spacing).
I think the inner turn hotter phenomenon might be more a matter of less
cooling air flow (that is, it's "inside") rather than an uneven
distribution of current or dissipation.
The real question is "how much performance increase will I get by
changing from AWG 12 wire to 1/4" copper tubing or 3/4" copper tubing,
or something like that.
hehe, yeah! Well, a power function across that primary impedance.
Some people do big power and DRSSTC's naturally heap power across that
primary. In those cases, there's a substantial difference between 1/4"
tubing and 3/4". But when power is low, there is no difference, just
wasted copper I guess.
I think we need to be careful about comparing things like "primary
temperature after running" because not only does a large tube have less
AC resistance, it also has more radiating/conducting area.
3/4" tubing has 3 times the "heatsink" dissipation area AND because the
turns are probably farther apart, better air flow.
For the same current, the dissipation in the 3/4" tubing will be 1/3, so
you have 1/3 the total dissipation in 3 times the area, so that's almost
a factor of 10... a huge difference thermally.
But in terms of "total power consumed in the primary losses".. maybe not
such a big thing..
The problem is, you can't ever say 3/4" is a
waste, because it's based on thermal dissipation and the power applied
across it. IF we're going to say yes or no to a question on copper size,
lets figure out how much power is being applied and if the tubing size
is risky or not. It is better to be empirically based on this particular
subject because of the many variables that occur and because this era of
coiling.
I think it can be done analytically with theory.. we just need to look
at the waveforms, etc.
SG's are being built and DR's are being built, and DR's are no
longer just a coil that is built now and then, many are doing it and it
wouldn't surprise me that they exceed SG coils soon in numbers. TCML has
always mainly had an SG knowledge base, and much of the information
received here is based on those experiences. It's all good, but times
are changing and solid state coils need to be addressed more. Primary
tubing size is simply a perfect example where SG and SS differ.
SS coils tend to run very low primary inductances, so the currents are
higher than in a SG coil, so, yes, primary loss in a SS coil is a bigger
deal. You also trade spark gap losses for switching device losses.
It's sort of like the difference between vacuum tube and transistor RF
power amplifiers. transistors have low output Z, so you need a whole
different design approach.
Back in the day I would think "well surely they understand were talking
about an SG coil using an NST"... problem is, I've run into SS coilers
that had a hard time even comprehending SG coils.
Yes.. it's a totally different beast.
As I came from spark
gap (SG), I had a hard time relating to these solid state guys until I
dived in head first (the only way to jump in). It's almost like a
generation gap. Would be cool if we could focus on both. I dunno, I
rarely do TCML post anymore simply because I'm doing solid state coils
now (exclusively).. there is just not a lot in here about that. But when
I see a post like this one, I have to add to it, because it matters ( I
don't want a solid state coiler getting the wrong impression I guess).
point well taken..
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