Name: Reinhard W. Buchner
AgeGroup: 26-30
CoilName: XTC-1
(pronounced "Extacy", but means eXperimental Tesla Coil #1)
CityStateCountry: Halsdorf, Hessen, Germany
E-Mail: RW.Buchner@Verbund.net
PageURL: http://rwbuchner.future.easyspace.com/
XformerType:
Modified 75mA NST. German NSTs are of low voltage design.
However, they can give loads of current. They are of open
frame design with no potting (the insulation is dipped in
HV varnish, however). I maxed out a 75mA NST to around
350mA. That is an increase of 467%!!! At this stage the
xformer does get pretty warm, but it survived many Jacob´s
Ladder experiments (seen on my page). At the 170mA, I am
running now, it stays absolutely cold, even though this is
a 226% increase in current (over it´s faceplate value).
XformerPowerClass: 1-2kVA
Xformer#: 1 (at this time; planned are 6 modified NSTs for 5-6kVA)
XformerInputVolts: 230V / 50Hz
XformerInputCurrentA: 7.5A
XformerOutputVoltage: 7500V
XformerOutputCurrentmA: 170mA
XformerLimiting: Internal magnetic shunt limiting
ProtectionSaftyGap: 0.75"
ProtectionBypassCapType: NONE
ProtectionBypassCapµF: 0
ProtectionChokeType: NONE
ProtectionChokeInductance: 0
GapType:
Multigap flat static gap. This gap uses two gaps made of aluminum. This results in a measurable increase in spark length. The exact reason is not quite clear. Most probable is the reasoning that the hefty ion migration causes the spark to be blown out. This gap does NOT use any kind of forced
cooling. I find this unnecessary due to two things: One being the relatively low current and the other being that I use a high number of gaps. A static gap will really thrive on the highest possible number of single gaps. The only real limit is the xformer voltage, but use as many as you can. It WILL improve performance.
GapGap:9 gaps a 1.1mm each
GapBPS:
Unsure. Definately more than 100bps. A good guestimate would be 300-400 bps. A static gap is NOT set to a specific firing rate, so this will vary with the gap setting and the capacitance of the primary cap.
CapType:
MMC. I was sick and tired of rolling and blowing poly caps. MMC stands for Multi-Mini-Capacitor. While Richard Hull at TCBOR had tried a similar configuration a long time ago, he had quite a bit of problems with blown caps and gave up on this idea. However, I have no real idea, how he built this primary cap. This type of cap never spread the word, like rolled poly caps did. I did lots of hard experimental work and find them fine for any TC configuration one can dream up. This includes low and high kVA inputs. I run many small MKP caps in series and several strings in parallel. This allows the tank cap to handle the voltage, the rms current and the peak primary RF current. For more information about MMC design and construction, please view the Pupman archives. I have written many, many articles on this cap design. One could say I am *THE* propagator of this *high tech* cap design. I run my caps at peak AC (V*sqrt(2)) = DC rating. I got quite a few scoffs at first, that this design would not last very long. However, people´s minds have changed and quite a few coilers have followed my design techniques and they are getting very good results. Cap failure is almost nill among many coilers and my caps are still doing just fine, even after long run periods.
CapµF: 0.067µF
CapKv: 12kVDC
PrimaryGeometry: Flat
PrimaryInnerDiameter: 11.8"
PrimaryWireLength: Sorry, no real idea. However less than 50ft
PrimaryWireDiameter: 3/8" soft copper tubing
PrimaryTurnSpacing: 3/8"
Primary#ofTurns: 10
PrimaryInductance: 23.44µH
PrimaryBestTap: 5.8-6.0
SecondaryWidth: 7.88"
SecondaryLength: 83.65 cm/32.93" h/d ratio= 4.1825
SecondaryAWG:
0.85 mm = AWG "19.5"
i.d:0.85mm = 0.033465"
o.d.:0.908mm = 0.035748"
SecondaryTurns: 920+1.25 space wound over 12cm/4.72"
Aprox wire length: 579m/1898 ft
DC resistance= 17.0 ohms
Calc´d inductance: 36.0547 mH
Measured 35.6 mH
Cself=14.75 pF
Bare secondary Q (measured) = 196
SecondaryFreq:
FresFree=218khz
Fresloaded =127khz
TerminalType: Dual Toroid
TerminalWidth:
T1 = 20"
T2 = 23"
TerminalHeight:
4.33" = 21.70pF
5.31" = 25.19pF
Ct(total):CT= 28.865pF (will be increased as construction continues)
SparkLengthInfo:
Spark length data from start of project till now:
-----------------------------------------------------------
0.) 5nF (a try at an oil-less) rolled poly design & 562VA NST. This made for 8-10" sparks.
1.) 15nF MMC & 562VA unmodified NST. This got me around 30" sparks
2.) 25nF MMC & 562VA unmodified NST. This got me around 41" sparks
3.) 31nF MMC & 900VA unmodified NST (I just turned the shunt out for 120mA).
This got me around 50" sparks. I never achived a single breakout. Break
outs where always multiple, even when the 50" connected to a grounded
rod.
4.) 67nF MMC & 1257VA modified NST
This setup only gets me around 57" average spark length. However, I do
get an occasional 63" spark.
NOTE: Spark length is measured "point to point". I do NOT "straighten out"
the spark. Doing so, would give me longer spark lengths, but the way I
measure the length is more realistic, I think.
I would say in the cases 1-3, I maxed out the spark length vs. input VA
pretty well. In the last case (current design stage), I need a much
larger toroid and the ~600A primary current are pretty much the limit
for my unblown static gap. I also tried increasing / decreasing coupling,
but it didn´t help in making the sparks any longer (making them shorter
was easy enough though :oÞ). Best spark length was achieved, when the
primary (!) was ~4.8" ABOVE the lower most secondary winding. Going up
to 5" ABOVE didn´t change it too much. I didn´t go above 5" as I have
seen racing sparks in earlier setups (i.e: in case 3) appear above 5".
Decreasing the primary heigth to 4" started reducing spark length. Primary
tapping is semi-critical. Moving the tap more than (+/-) 1/4 turn will
let the output drop like a rock. None of the above MMC are mains reso caps,
although case #3 does come pretty close to it. Optimized, I think I can get
around 65-70" from this setup.
RFGroundInfo:
I use zinc coated (for long life) T-iron. My RF-ground is composed
of 4 pieces of 5mm thick x 45mm wide T-iron, each about 4 ft long.
These are pounded into the ground about 4 ft apart (length of the
T-iron is the width of the spacing in between). T-iron has two real
advantages: It is nearly impossible to bend. The "T" form is VERY
strong and iron is stronger than copper. You can smack away at it
with a hammer and it WILL go into the ground straight. It won´t be
affected by rocks (unless there the size of a large brick). My
backyard contains a lot of smaller rocks and sand. If you use your
good old angle grinder to sharpen the bottom of the T-iron to a mildy
sharp point, it will almost slip into the ground just by looking at
it. (okay, okay, I admit: not quite) The second advantage of T-iron
is the surface area is much, much larger than a piece of round rod
(which is why I never understood why coilers use rods at all). 3 of
the four T-iron pieces are about 1ft underneath the sod level and
the last one is about 4" above ground level. I painted it red for
visibility and it has a sticker on it that says: "RF-ground" Do
not remove". You wouldn´t be able to anyway. Once the thing is in
the ground, there is almost no way you will get it back out ;o)).
A brass screw (plus a little bit of grease to prevent corrosion),
fastend with a normal lockwasher and nut makes my connection
terminal. I use a wing nut on top of this to connect my grounding
wire (35mm^2 = AWG 0), which has a normal (big) soldering lug on
it. Forget about using a single ultra long piece of rod. It is much
easier, and from an RF standpoint actually better, to use several
pieces of shorter rod (or T-iron for that matter :ö). It only took
me about 2 hrs. total to make the whole RF ground, including getting
everything together, the work, replacing the grass (so my mom doesn´t
start getting upset about her "ruined" lawn), and cleaning up. My
method: no sweating, no cursing, almost no digging and it makes a
pretty good grounding system, or at least my coil seems to think
so. (:o)). I cannot stress the need for a VERY good ground system
enough.
OtherInfo:
Pri current: ( for the current design stage)
= V*SQRT(C/L) = 10606V*SQRT(67*10^-9F/23.44*10^-6H) = 567A
With my present MMC design, this works out to 43.618A per cap
string. The peak primary current will be above the 1.2kA level
in my final design. My MMC stays ICE cold, even though I ran
the coil for a total of 1.75 hrs (a few minutes at a time, cool
down time was low, as the coil was off only during adjustments)
at the 567A stage. Total run time on these caps is around
3.5hrs.
Primary Joules:
0.5*7500V*sqrt(2)*(67*10^-9) = 3.77J.
The final design will up this to around 12-13J
The spark length in the final stage should be at LEAST 118" (~10ft),
although I have done some calculations showing me the output might
be closer to 12ft.
This coil was designed (with a "low" primary voltage of 7500Vrms or
10606Vpeak) to clear up some of the myths in coiling, such as the
"need" for high voltage xformers (i.e. >>9kV). It makes ABSOLUTELY
(as also recently (May 1999) proven empirically by John Freau.) NO
DIFFERENCE, if you run a coil with low voltage, high current (and a
big primary) cap or if you go the more conventional way of high
voltage, low current and a small primary cap. The ideal voltage range
lies between 6-16kV. Going any lower will result in gap problems and
going much higher than 16kV (all values are rms!!) will result in
corona problems. The low voltage design does have one disadvantage
(for high power coils): you need a spark gap design, that will handle
high currents. However, the low voltage approach does have an advantage:
As the voltage is low and the current high, this kind of xformer
makes a VERY stiff psu (power supply unit), which is an important
consideration. esp when designing a high breakrate coil.
I think secondary preparation is of outmost importance, if you want to
dabble with high input power and high coupling factors. My PVC form
was sanded, force dried, coated inside and out with PU varnish and
allowed to harden. Then the wire was wound on the former. I used a
homebuilt winder to aid construction. The wire was wound under constant
tension. I also made sure that the wire was not kinked and there was
only minimal space between the turns. The whole form was coated with a
slow drying (24 hardening time) expoy resin, sanded, coated with a 2nd
coat of resin, sanded once again, coated with PU varnish, sanded and
given a final coat of PU varnish. This makes the coil and former glass
hard and very smooth. The electrical properties of such a coil
construction are very good (you can really stress it). As a matter of
fact, during a run, my primary coil tilted and I got hefty flash-over
between primary and the secondary coil. I shut down and examined the
coil. My coil survived without the slightest mark. I am 100% positive,
that if I had not finished the coil the way I did, it would have been
trashed during this experience. My primary is 5" ABOVE the lowermost
secondary turn, so coupling is very high (actual value must still be
measured). If the wire was not "embedded" in epoxy and PU varnish, I
am pretty sure I could NOT couple this high. I also have a "screw on"
RF ground conenction. I do NOT like the RQ/TCBOR RF ground connection
technique. Please have a look at my page for more info at http://
rwbuchner.future.easyspace.com/tesla.html on my secondary coil design.
Coiler greets from Germany,
Reinhard
(
geocities.com/southbeach/pier/2756/teslasurvey) (
geocities.com/southbeach/pier/2756) (
geocities.com/southbeach/pier) (
geocities.com/southbeach)