Re: Large H/D ratio Secondaries

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Dr. Resonance" <resonance-at-jvlnet-dot-com> 


1400-1600 turns with a h/d ratio of 4.5:1 works great on most all coils.

Select your coilform dia.  Next, multiply by 4.5 to get the correct winding
length.  Last, divide this winding length by 1500 (as an example) and you
now have the correct wire dia.

Use a chart to look up the correct wire AWG from it's dia.  We always use
200 degree C wire due to the much heavier insulation especially if the coil
is running sparklength of 48 inches or greater.

This composes the entire procedure for wire selection and determing the
correct AWG to work with a 4:1 h/d ratio.

It's simple, quick, and always works.

Dr. Resonance


 >
 > Just finished my first sensible TC secondary attempt.
 > Like to build more of these after this first one is
 > tested... Years ago I built a large sonotube model
 > using just some 270 winds of ordinary household
 > insulated 14 gauge wire, that secondary only made 2-3
 > inch arcing, at 1.5/1 H/D ratio. Then the quarter wave
 > deviance was still obvious, near 210 Khz vs 166 Khz...
 > Of course the finer gauge wire secondaries deliver
 > more of the effect of arcing so my second try is
 > sensible, about 925 winds of 23 gauge wire on 4.5
 > diameter schedule 40 PVC pipe, just over 22 inches
 > h value so the H/D ratio is then 4.88
 >
 > A look at Paul Nicholson's excellant chart at
 > http://www.abelian.demon.co.uk/tssp/misc.html shows
 > that we might expect the highest deviance values of
 > quarter wavelength values at the higher H/D ratios. I
 > noticed on his chart that the midrange H/D ratio is
 > between two and six, so this a large range, but I did
 > not base my primary frequency designation according to
 > that chart, but just went with the quarterwavelength
 > "approximation used as the first estimation of the
 > probable resonant frequency" was how I based my
 > primary tuning circuit on, which is the ~quarter
 > wavelength of my coil being about 225,000 hz. Loh and
 > behold my first firing produced hardly nothing on the
 > secondary, even with Oudin connection to primary.
 >
 > What I had assumed was that when one typically adds a
 > globe to the coil as a top load, this also reduces the
 > resonant frequency, so then in contrast we might still
 > use the quarter wave method and still at least get
 > some kind of decent arcing. But according to Paul's
 > good advise for large H/D ratios;
 >
 > The 1/4 wave resonant frequency of a wire, when wound
 > into a solenoid, is typically more than 50% higher
 > than that of the straight line value.
 >
 > Of Course I didnt use Medhurst changes either, but now
 > I see how a tesla coil project can get a little bit
 > challenging, and it just aint a simple thing to
 > predict a resonant frequency.
 >
 > According to this thing I should retry the coil for
 > 337,000 hz and expect the secondary to then respond.
 >
 > Another question I have is how close to the demand
 > value of capacitive draw is best for operation. My
 > first guess called for 25 nf, using 20uH primary but
 > the supply was only able to pass its full current at
 > 5.3 nf at rated value.(not considering resonant
 > effects) Having 4 of these NST's in parallel would
 > meet the demand of the supply. It has been stated
 > 1.5/1  is okay for LTR operation. Doesnt this mean
 > that the inductance of the primary design would be
 > dependent on the amount of supply being made by the
 > estimated transformers in parallel? For example at
 > 20uH primary,using 25 nf capacity; 4 transformers
 > would be needed to meet that capacitice reactance draw
 > supply but higher inductances of primaries,in turn
 > mean lower capacitive values being employed for the
 > resonances, where then the demand comes closer to the
 > potential amount of supply so for any pariticlar
 > design, the amount of transformers in parallel should
 > be structured to be 150% of the estimated draw,
 > according to that LTR premise.
 >
 > In fact on the first firing based here, the demand is
 > four fold far more then the supply, but a narrow arc
 > gap is used to neccesitate arcing at about 100 volts
 > variac to primary. No significant secondary effects
 > were noted at that estimated 225,000 hz employed as
 > primary combination. A retry at higher frequencies
 > seems sensible.
 >
 > HDN
 >
 >
 >