[Prev][Next][Index][Thread]
Re: Number of turns for a secondary?
Jim,
Looking at 48 coils, I sorted data by arc length. This is what I found (on
average).
Secondary HD ratios are consistent throughout the range.
Secondary lengths increase as arc lengths increase.
Secondary diameters increase as arc lengths increase.
Again, HD ratios are kept in balance, even with bigger coils.
What follows arc lengths more consistently than either lengths or widths is
the
total secondary self capacitance. Interesting is tank inductance does **not**.
Tank inductance is seriously scattered throughout the range. Tank capacitance
however **does** follow. Tank capacitance increases with the secondary self
capacitance.
(I've decided not to throw up more graphs as I'm in process of collecting more
data and want to wait until I can enter it all).
So, based on just that bit of info., HD ratios are kept in balance
(ultimately)
by matching wire size to diameter of coil and by keeping the number of
turns in
balance (number of turns are pretty consistent throughout the range).
But keep in mind, 98% of these coils are close wound. The data shows what
happens
when we construct our coils the way we do. But, there is not a lot of data to
show what happens when we vary from the norm. Suppose we space wind a coil
at the
same diameter as the wire diameter and compare that to a closewound coil of
the
same wire diameter (keeping turns and HD the same). With the space wind, Cself
will double! If we keep our primary tank inductance constant with some
arbitrary
value that our closewound coil is set at, then the tank capacitance will
need to
be increased by about 2.5 times. The output energy per bang will follow this
increase (and so will arc length). We also end up with a secondary twice as
wide
and tall.
Now imagine if we built a big coil without increasing wire size (same
scenario).
Cself is decreased, Cp is decreased, output energy is decreased, arc length is
decreased, and the coil is much shorter and thinner (which may or may not
play a
performance role). With this scenario, doesn't it make sense why one would
want
to put on a big top load thus increasing the total secondary capacitance
and all
the good things that follow?
I think what should be realized, is long arc lengths need some room for
arcing.
Build a high powered coil with the top terminal 5 feet from the primary
inductor,
and you'll hate your self. It will be very difficult to keep the arcs off the
primary winding or strike rail. You will definitely want to allow some length
which is going to open your window for field control of the arcs. A good
example
of field control is Robert Stephens photo's at my web site or Chip
Atkinson's web
site.
You'll notice arcs out and around the primary components.
http://www.geocities-dot-com/CapeCanaveral/Hangar/3108/rwsmap3.html
or
http://www.pupman-dot-com/current/rstephens/index.html
When allowing for secondary length and still keeping HD and turns in balance
(closewound), you will be required to increase your secondary wire diameter,
which will also increase your total secondary self capacitance due to the
increased wire surface.
What I see up and coming with this data is a relationship between arc
length and
energy which is directly related to total self capacitance. If this
relationship
exist with some consistency, I think we are going to find how large our top
capacitance should be for optimum arc length performance based on the
secondary
coils stand alone self capacitance (what is too large and what is not large
enough). All this is still be seen.
Hope I got this right (and didn't confuse too much),
Bart
Tesla List wrote:
> Original Poster: Dsurfr-at-aol-dot-com
>
> This thread has made me curious as I plan on winding a larger diameter coil
> soon myself. I always thought that you decreased the gauge of the wire
(fewer
> turns per inch) to keep the H/D ratio compatible with the number of turns
> (ideally somewhere between 4:1 or 5:1 & under 1000 turns). I thought that
was
> why (aside from the current being carried) the larger coils always used a
> heavier gauge wire. Like I said I'm just curious & I know a lot of other
> factors come into play in the design. Thanks, Jim