Hi Bart!
Finally got some time to sit down and read my mail! LOL After last
weeks "research" mission I decided to give myself some dedicated
workshop time this weekend! (Not that I actually have a workshop or
anything so rather just read that as "hands-on time! LOL)
Am actually quite excited to test the fruits of my labour and see the
results! With the increased power requirements of my next coil and the
fact that I am going to need/want to configure and optimize it's tank
circuit I decided to build a robust but completely modular parallel
plate primary capacitor with individual plates of varying capacitance
and power ratings giving me the ability (hopefully) to configure and
adjust my cap to the coils needs ad-hoc! To this end I came up with a
design this weekend which (I hope) makes best use of the materials I
had available! Happy to say that the first plate (using a carefully
chosen sandwhich of multiple dielectric materials) is now undergoing
it's "compression and vibration degassing" phase! *g*
Would love to have gone the MMC route but after 2 weeks of searching I
simply could not finding suitable caps at an affordable price here in
SA. Oh well, at least I get the opportunity to learn more about
materials dielectrics/losses/suitability/ratings/etc. ;-)
LOL Sorry, didn't mean to write an intro essay! Grrr
THANK YOU for your reply to my post! Most appreciated!
I agree, I should definitely be more careful with my choice of words!
I used "WANT" at that time because, in my state of confusion, it
seemed like a good idea to use a choice of frequency and thus it's 1/4
wave as a solid starting place for the design of the coil!
Of course, now that sanity has been returned, I do see where I went
wrong! I am however still of the opinion that I do need to include the
frequency (ranges) that I WOULD LIKE to run the coil at, into the
design, not only to optimise the coil for a specific type or length of
spark, but for a good few other reasons as well which I would like to
discuss.
Going back to my RC aircraft flying days I remember a saying I heard
often .... "ANYTHING will fly if you give it a big enough engine ...
even a brick!"
The same of course holds true here, ... you could pretty much get any
coil to do anything you wanted it to by giving it more juice, driving
it harder, etc. ......... at least to some degree!
To my meaning, there is generally however always a "gotcha" or
trade-off in this regard. Yes, if you do give it a big enough engine,
that brick WILL fly; BUT, noone said that making it fly was in the
brick or engine's best interests!!! ie. amongst other things, the
lifespans of both are going to be very seriously diminished! *GRIN*
The point is that I have it in my head, that at least to some degree,
choosing and designing around (albeit loosely), parameters like the
coils "normally" operating frequency ranges will, in the long run,
make for a happier coil and unstressed components with a increased
lifespan and reduced eunning and ownership costs. ????
This, IMHO, is the difference between a coil which lasts for years
with very little maintenance and will happily run for a couple of
hours a day, and that other coil that forever needs a little coaxing,
regularly blows a cap (or somthing), isn't fired up too often, and
when it is, can only be run in short intermittent bursts due to
overheating in one or other of it's components!
A little long wind'ed but I hope that explains my "FREQUENCY FIXATION"!!! ;-)
Just a quick note here ... did you not notice that I was in a major
info overload condition and sitting on the verge of sanity??? You
should be reported to someone for blatant use of knowledge which could
have sent a lesser being straight to the madhouse! *joking of course!*
LOL
"FUNDAMENTAL FREQUENCY" ........ WOW!
You have certainly ensured that I am going to be a fan of yours for a
long time to come! *chuckle*
While I was reading your reply I realised that my knowledge of
"inductance" is not what it should be and I have a long way to go to
fully understand all that you said! If you, or anyone else has booster
material or references (The Idiots guide to Inductance) that could
help me get up to speed in this regard I would appreciate it greatly!
I remember the formulaes for calculating LC/RC/LCR circuits but am
embaressed to say that my understanding of inductors is running around
the NIL mark at the moment.
The same now holds true then for a coils fundamental frequency and how
it is calculated, measured, designed, changed, etc. so I will be
forevr grateful for any additional information you could give me in
this regard.
Many many thanks in advance
Grant
Randburg, South Africa
bartb <bartb@xxxxxxxxxxxxxxxx>:
Hi Grant,
Something that caught my eye is that you "want" the secondary wire length at
1/4 wave. I hope this is only a "want". A coil of course does not require
this for best spark performance. If you "really" want the secondary wire
length to be 1/4 wavelength (such as antenna theory, radio circuits, etc.)
then realize you can't use a top load. A top load will capacitively load the
secondary significantly and change the distributed capacitance affecting the
coils frequency (far from the wire length). Spark propagating coils are
tuned to their fundamental frequency which may be close or far away from the
1/4 wire wavelength situation. The wire length has no bearing on the
resonant frequency. The resonant frequency of a coil is a composite of all
the capacitances (objects) which affect the coil as well as the inductance.
But it doesn't stop at simply object capacitances causing the change. With
increasing frequency and with coil geometry (h/d ratio, spacing ratio,
etc..), the currents along the length of the coil are also affected. This
causes variations in inductance along the coil. If you could measure the
inductance of each turn say on a 1000 turn coil, not all turns would measure
the same inductance (even though the wire size, geometry, and length are the
same). The current affects the emf and thus mutual inductance to adjacent
turns, which in turn affects the inductance of each turn itself. If the
current varies, so does the inductance. But if you calculate those currents
along the form at the fundamental and lump the inductances, you'll find the
"real" inductance at the fundamental frequency (which is different than say
a DC inductance or even 1kHz LCR inductance measurements). By the word
"real", I mean the inductance which is affecting the fundamental frequency.
This situation also affects the 1/4 wave wire length precursor because of
the inductance at high frequency (which is any frequency above DC which
adversely affects the inductance). So even our lowish frequency 100kHz coils
will have an effective inductance at the fundamental which will be different
than the wire inductance.
By all these "words", I'm simply saying that to actually make a 1/4 wave
wire length equal to the fundamental is no small task. Wheeler and Medhurst
equations won't help here. To do this, you really need a bare secondary by
itself. Even a primary coil is seen as an object to the secondary that will
change the situation. Coil height to ground, walls, and miscellaneous
objects do the same. But to do it in a dual-resonant coil situation can only
be done best with just those 2 coils and nothing else. Even using a little
small sphere as a top load (to reduce Ctop) affects the coil a tad. It can
be done that way, but if you want a spark performing coil, then this isn't
the way to go about it. It causes many limitations to the coil design which
affects performance.
If we ignore the 1/4 wave length wire theory, then we really only need to
worry about the fundamental frequency regardless of the objects on or around
the coil. This type of design makes for good sparking coils because we now
have freedom to play with primary LC values to match whatever fundamental
frequency the secondary coil ends up at.
So it's hard to give advice. If your set on "1/4 wave wire length" as a
precursor, then you have your work cut out for you. Is this really your
train of thought on this coil?
BTW, 9 to 12 turn primary? No. This is only a "common" value we tend to end
up at. Some coilers use over 20 turns and a few only use 2 or 1. What is
meant I think is that higher turns adds impedance which helps attenuate the
voltage on the primary for less problems and may even help with quenching.
But no one is saying this as though it is wrong to use less than 9 turns.
Simply that "some impedance" has been noted to help with gap quenching.
ALSO, coupling you mentioned. No, coupling is fully adjustable. It's just
that you "can" make a coils coupling to whatever you want and still have it
even with the bottom secondary winding. For example. Suppose a coil builder
is use to building a set distance from primary to secondary. And if the
primary is even with the base, he usually ends up about 0.13 k on the
coupling for the same coil size. Now say he lowers the primary to reduce the
coupling and ends up at 0.11 which he finds best. Well, the primary itself
could be redesigned so that when the primary is even with the sec base, he
ends up at his found 0.11 ideal value. Thus, he ends up not needing to
adjust the coupling. That's all there is to it. But adjusting the primary
height is also perfectly acceptable and usual (since coilers don't seem to
know what works best for a particular coil geometry).
Best regards,
Bart
Grant Visser wrote:
Hi there,
Suffering from sleep deprivation or 18 hour research / calc / sim /
research .... info overload at the moment, or BOTH! lol
With my limited budget I am on a mission to get a solid base design
into my head before I begin throwing things together as I did last
time! *grin*
The problem is that I have now done so much reading of content from so
many different viewpoints (over the years) that I have confused myself
COMPLETELY! Thus, I humbly beg your assistance ... or at least just a
darn good kick in the right direction!
I have in front of me 26.06" of 3.543" Plexiglass tubing with 3mm
(0.1181") wall thickness (and don't want to waste a single mm of it!)
lol
Assuming 220V 50Hz mains and 2x 9KV/40mA NST's to power my new
coil(/s) (could add another 2 very soon!!!)
3Kg of Double insulated magnet wire about to be ordered, ex works in
either 0.335mm (0.013188"), 0.355mm (0.013976"), 0.375mm (0.014763"),
or 0.4mm (0.015748") OD
Have tried my best but am not going to be able to afford the (less
than ideal) caps for a solid MMC so have decided that I will build a
quality bank of vertical plate caps for this coil. They'll never go to
waste!
I have also decided (I think) to go for a balanced split cap tank design.
Until I can find a decent blower I'll be using my current suction
quenched adjustable 2 gap design.
1/4" copper tubing for the flat pancake primary coil
Oh, and yes I do now have a SOLID and dedicated RF Ground.
I do also have 3phase at my disposal .......
Although it didn't even cross my mind initially, one of my biggest
stumbling blocks at this point is at what frequency I am going to run
this coil. This quandry started when I read a few posts from awhile
back regarding the primary winding and that it should have no less
than 12 to 15 turns and tuned at no less than 9 turns, and ensuring
that the final diameter or the primary is the same or close to the
winding height of the secondary! Apart from the fact that it actually
made sense to me from a coupling point of view, it also meant that I'd
be able to use a smaller main cap, so I was very happy right up until
I started doing the math / sims and it meant that I was going to have
to use a "SMALLER THAN RESONATE" capacitor which, seems to be an
absolute no no if I have understood the numerous other posts and
articles I have been reading!
A further brainmangler that has crept in now is the other concept that
I had forgotten about ..... and that is that I would want to design my
secondary to have the length of wire I need to resonate with my
primary at a 1/4 wave! ie. At 220KHz the 1/4 wave is at 1118.1818ft
and I should thus use exactly that length of wire to coil my
secondary. Again this all makes perfect sense ....... right up until I
start doing the math and the sims ....... at which point, depending on
which program I use to model my coil, either the program yells insults
at me, or I simply cannot find a workable solution which allows me to
use all of the data above AND have a resonate coil with a decent hd
ratio! Going much below 220KHz means that I would have to increase the
length of my coiling wire to seemingly crazy HD ratio's!
Now I do absolutely want to achieve the longest possible sparks from
this coil and I would like it to be an unstressed system allowing long
run times. I would also however like to use this coil to begin
demonstrating and researching the concepts of powering up light bulbs
etc from the ground waves for which I am going to have to construct a
top load with no breakout! With this in mind I was hoping to either
split the 26" form in half allowing me to coil two seperate identical
secondaries and use the second in a magnifier configuration. OR .... I
was even considering (but had not yet begun much research) using the
form for a BIPOLAR coil!
I do realise that 3.5" is not exactly a MEGA COIL but it did seem to
me that it could be a nice little testbed to get me started with some
of the more interesting experiments! ???
SO! Thats where I stand at this point! More confused than ever and
really hoping that you will be able to help me back onto the straight
and SPARKY!
Grant Visser
Randburg, South Africa
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