- white PVC pipe
- diameter: 1.18 inches (3 cm)
- wound lenght = 6.49 inches (16,5 cm)
- total lenght = 7.87 inches (20 cm)
- number of turns = 660 with 0.25 mm magnet wire
- calculated inductance L = 2159.69 microH
- calculated C self = 2.4691 pF
- F res without topload = 2.180 MHz
- the secondary is insulated inside with plasticine to prevent breakdown
- no varnish
TOPLOAD
- made with different sizes bells taken down from electric bells. Capacity unknown, empirical tuning. The sharp edge of the topload was insulated with plasticine
PRIMARY COIL
- average radius = 3.54 inches (9 cm)
- wound lenght = 1.96 inches (5 cm) at 2 cm from bottom
- total lenght = 15 cm
- number of turns = 6 , with solid 3 mm copper wire, 7 mm space between turns
- calculated inductance = 8.7667 microH
PRIMARY CAPACITOR
- MMC style cap made with 7 (10 nF @ 2 kV) polipropilene caps, in serie for a 1.42 nF @ 14 kV cap
SPARK GAP
- simple with two big heatsinks, 5 mm gap
STEP ONE
DIMMER DRIVEN IGNITION COIL
RESULTS: 3 - 3.5 cm streamers, 8-9 cm arcs to ground
For easy comparing I used a 9 V battery which has a 4,5 cm height, / the PVC pipe that supports the grounded electrode is 4 cm diameter
MODIFICATIONS
I put a 6.8 nF@ 2kV polipropilene cap in parallel with the primary of the ignition coil. It seems to help the streamer output and the IC is cooler now. 8 uF in the dimmer-cap combo seems to be a good compromise between high current output and the heating of the coil.
- wound on white PVC pipe with end caps (plasticine)
- diameter: 1.56 inches (4cm)
- total lenght: 9.05 inches (23 cm)
- wound lenght: 7.87 inches (20cm)
- number of turns = 800 with 0.25 mm magnet wire
- no varnish
- inductance (calculated): 4542.41 microH
- self capacitance: 3.0784 pF
- self resonant frequency (without topload): 1.346 MHz
I added 1.1 nF at the primary cap (I am using 2.5 nF now). I tryed a
Cp = 14 nF, but the spark gap didn't fire up. So I will stay under 10 nF, better under 6 nF.
The high coupling seems good for these low power coils. I made a new primary, adding 4 more turns (insulated top turns) to the old primary. Specs:
- PVC form with plastic spacers
- diameter: 7.08 inches
- wound lengh: 2.95 inches
- number of turns: 10, taped at turn 8
- inductance (calculated): 13.07 microH
RESULTS: 5 cm streamers, 11.5-12.8 cm (5 inches) arcs to ground
Last time I had some racing sparks on the secondary. I didn't want to lower the coupling too much, but I will make a shorter primary without interturn spaces to match the wanted inductance. I made the primary using 10 turns with highly insulated trifilar cable (3 x 2.5 mm), connecting all 3 cables in parallel to decrease the ohmic resistence.
In an attempt to tune the TC I made a new topload with a floater covered with alu foil (yes, the little plastic ball from the water reservoir of the toilet). The spheric topload is useful for little coils because the coalescence tendecy of the streamers, preventing power dissipation in multiple streamers. The little metalic bells under the sphera are used to supress corona at the top turns and getting the thing into tune (by adding or substracting them).
RESULTS: 5 cm streamers, up to 7 inches arcs
INCREASING THE PRIMARY CAP
I used a new smaller cap 3.6 nF (original 2.5 nF and a MMC chain with 8 FKPs in serie, 9.1 nF @ 1600 V each). Primary made with trifilar insulated cable 6 3/4 turns, spark gap = 5 mm. Wunderbar! It works great. The streamers are up to 8-9 cm and the ground arcs are between 12-14 cm. Seems that increasing the Cp value, the streamers are longer, but the ground discharges are a bit shorter, though very bright. I tryed to get a higher current output from IC using 3 uF more in the dimmer- cap combo. It didn't affect the spark, but the iggy run hotter. So I will go with only 8 uF. Rising the secondary with 1 cm helped a lot the streamer display.
Experimentally I have now some observations:
PRIMARY CAP (nF) SPARK LENGHT TO GROUND TC BEHAVIOUR
1.1 nF 9 cm run smoothly
2.5 nF 17-18 cm run smoothly
3.6 nF 12-14 cm disruptive
5.8 nF 10 cm very disruptive
Seems that for the dimmer- cap driver, the magical value for Cp for long sparks stay somewhere between 1.5 - 3.5 nF.
TWIN SETUP APPROACH
In an attempt to increase the spark lenght, at the same power, I made a twin system, but the sparks didn't grow above 8 inches.
FLYBACKS
A NEW CHALLENGE
I bought two unrectifyed flybacks, one from an old TV with tubes (let say flyback A) and the other with a bigger core from a colour TV (flyback B). I took off the spacers on the flyback B, eliminating the gaps on the core, preparing it to get some more power (acting as a transformer) The driver was my old Royer setup (http://www.geocities.com/teslina/Rfsch.html). The primaries of the flybacks were rewound witH 4+4 turns and a Cp = 6 uF @ 600 V
The output of the two transformers is not similar. The flyback A outputs a flame like arc even at a low voltage from the variac (5 VDC). The flyback B needs more voltage (20 VDC) to output some scary arcs. Under load, the driver IGBTs warm a bit with the flyback A but remain stone cold with the flyback B
Because of the higher working frequency I have to rectify the flyback output to get an efficient charging of the primary cap in the primary tank of the TC. I didn't trust the diode split transformers and wanted to use some external diodes. Because I dont like silicon in a SGTC, I tryed first with a vacuum diode, but the result was dissapointing. So I managed to get some TV-20 silicon diodes. The diode have to be overrated for more safety, so i used at least 4 in serie (I am using 6 in serie curently now). The diodes heat up a lot with the flyback B (probably because higher circulating power output), but the warming is resonable with the flyback A in place.
I made a quick setup, with driver, flyback A/B (each flyback can be put in the circuit), rectifyer (6 silicon diodes TV-20 in serie), a 1.4 nF cap as load (capacity comparable with the primary cap of the TC) and a spark gap in parallel with the cap, to verify the functionality, temperature on flybacks/ diodes/ driver IGBTs. The results are sumarised in the next table:
Transformer Arcs (without load) Input voltage (variac) Diode warming IGBT temperature
with 1.4 nF load with 1.4 nF load
Flyback A (with gaps) brigther as a flame low (from 5 VDC) warm warm
Flyback B (no gaps) strong arcs surrounded higher (>20 VDC) hot cold
by an incandescent gas
column
Seems that the flyback B offers some real advantages as output and driver security, but it heats up a lot the recTifyer limiting the run time (possible much higher if would try to charge bigger caps) and needs more voltage to get the same ouput as the flyback A.
First of all I used the flyback B (no gaps), my hope for big sparks. But....it suxx! No streamer output and only some faint discharges to the ground. And I had to put a lot of power in it (hot primary) to get these pathetic results.
- 4 cm diameter secondary (the last used)
- 10 cm diameter sphere as topload
- 6 turns compact helical primary
- 3.6 nF @ 12 kV primary cap
RESULTS: 7-8 inches streamers
I made more pics, using a film camera ( mode B, ASA 200 film, f = 5.6, 2-4 seconds exposure time). I had no tripod, so the pics are a bit shaken. Sumation pics can capture the maximum lenght of the streamers.
Because the DC charging, the primary capacitor remains charged after the setup is turned off. Even after discharging the primary cap, the residual charges will build some high voltage which can shock you (from my painfull experience). So, pay attention, and if you want to modify the setup, use some clips to short the spark gap electrodes temporarly.
I didn' t think that a small flyback can output such more power, so, I decided to upgrade a bit the primary cap to see how it behaves.. Though, if I would increase the primary cap, I have to use lesser turns on the primary, so more losses in the spark gap. Hmmm...I will use a bigger secondary this time:
SETUP
- white PVC pipe
- total lenght = 27.2 cm
- wound lenght = 24.5 cm (9.64 inches)
- diameter = 7.5 cm (2.95 inches)
- N = 980 turns
- no varnish, end caps glued
- calculated inductance (L) = 18930.296 uH
- calculated self capacitance = 4.5119 pF
- self resonant frequency (without topload) = 544.85 kHz
- self resonant frequency (with toroid topload) = 348.5 kHz
TOROID
- cross diameter = 1.96 inches
- outer diameter = 7.87 inches
- calculated capacitance 8.6889 pF (6.5167 on secondary)
PRIMARY CAP
- MMC style with 7 x 100 nF @ 2 kV in serie for a total of
14 nF @ 14 kV
PRIMARY COIL
- 18 cm compact helica primary 7+3/4 turns
SPARK GAP
- simple, 2 Al heatsinks, 5 mm gap
The streamers are very small because the BPS is very low (approx 1/sec)
NOTE: a sphera topload would be better. For the same cross diameter, the sphera offers a smaller surface than a toroid lowering the potential lines distribution along the circumference. It would output only a few streamers that tend to unite.
After all these experiments, seems that a 5 cm diameter secondary, with 900-1000 turns wound with 0.2-0.25 mm magnet wire, with a spherical topload, a 4-5 nF primary cap with a high coupling helical primary, would be the best design.
SINGLE STREAMER OUTPUT
THE NEW SETUP:
- grey PVC pipe, not varnish, plasticine ends
- diameter = 1.96 inches
- total lenght = 9.05 inches
- wound lenght = 8.46 inches
- N = 1075 turns with 0.2 mm diameter magnet wire
- calculated inductance = 11880.35 microH
- calculated self capacitance = 3.5022 pF
- resonant frequency (without topload) = 780 kHz
TOPLOAD
9 cm diameter plastic sphere covered with alu foil
PRIMARY
6+3/4 turns compact helical primary wound with 2 mm diameter
plastic insulated copper wire. Primary at 1 cm from the secondary bottom.
PRIMARY CAP
3.6 nF @ 12 kV, MMC type
P = Ec * BPS
where P is the power in the system (burned in the streamer), Ec = the energy in the primary cap (=Cp*(U)^2/2) and BPS = the number of bangs per second. The lenght of the streamer is proportional with the power (streamer lenght = k * sqrt(P), k = 1-1.5). So, we would have three possibilities:
1. increasing the cap value (but the high capacitance would decrease the BPS though)
2. increasing the voltage input
3. high BPS, making a compromise between chosen Cp and BPS. We have to keep in mind that BPS depends also by the current capabilities of the high voltage source (flyback transformer in our case).
So my chois this time, was the third variant, because I wanted to get a special effect - unite all the streamers on topload in a single one (burning all the power in a single long streamer). This can not be done with high Cp and low BPS. Bigger primary caps give multiple branched streamers.
The single streamer phenomenon can appear by itself, or been provocated by strong discharges to ground, which focus all the streamers in a single discharge channel.
RESULTS: 20-21 cm single dancing streamers (like in a plasma ball but in free air)
- bigger flyback, or modern DC flyback, which can output DC HV up to 20-30 kV
- bigger primary cap (up to 5 nF), voltage overrated
- larger spark gap (multigap for easy quenching), to get more charging voltage on the primary cap.
Philer used this approach and got up to 20 cm streamers and 22 cm ground discharges.
I feed mine with 20-25 vac from a variac. Below 20 vac, the streamers don't form well. Above 25 vac the sparks tend to decrease, and the spark gap and flyback run hoter.
Robert moved the things further. He used a huge primary cap and a big secondary to make 45 cm sparks. His setup:
- secondary: 16 cm diameter, 45 cm wound lenght, 2000 turns with 0.2 mm magnet wire
- flat primary, 10 turns, taped at last turn
- toroid: 22 x 7 cm
- primary cap: 50.3 nF
I used this system a bigger setup (my big DRSSTC secondary together with a new built primary).
- total lenght = 21.65 inches
- wound lenght = 20.98 inches
- pipe diameter = 4.32 inches, D/L = 1/4.8
- 2665 turns with # 32 magnet wire
- calculated inductance = 144547.81 microH
- self capacitance = 8.3143 pF
- resonant frequency (without topload) = 145.25 kHz
TOPLOAD
- medium toroid : 16.3 pF with a nail
PRIMARY
- big basket wound with 11 turns (2.5 mm solid copper wire)
taped at turn 9
PRIMARY CAP
= 100 nF @ 12 kV
I started increasing the primary capacitor in my last setup to 130-150 nF. The spark lenght didn't increase too much (only 52-53 cm), so I thought to use more secondary inductance to match the big Cp.
SECONDARY
- white PVC pipe (my Royer SSTC secondary)
- diameter = 14 cm
- wound lenght = 47 cm
- 3760 turns with 0.125 mm magnet wire
- calculated inductance = 509728.72 microH
- calculated self capacitance = 8.5494 pF
- self resonant frequency without topload = 76.2 kHz
TOPLOADS
- three stacked toroids: little (8.75 pF), medium (11.77 pF) and big (16.3 pF)
Total secondary capacitance = 45.36 pF
10 cm nail on the upper toroid
PRIMARY
- flat style, inner diameter = 30 cm, outer diameter = 35 cm
- 11 turns wrapped together, taped at 8 turns
PRIMARY CAP
- 200 nF @ 12 kV
SPARK GAP
- simple gap between two massive alu heatsinks. The gap is set at 4 mm. If we
consider the air breakdown at 30 kV/cm, that means 12 kV ignition voltage.
Smaller gap will not use the entire charging capacity of the source. With the
big heatsink electrodes the gap stay cool. BPS = 1-10.
Discharge the primary cap everytime you want to make system modifications, or use resistor bleeders. 200 nF @ 12 kV IS LETAL !!
Even touching a single armature of the cap will produce a discharge at this voltage. Use a solid insulated cable to short the cap between run times. Protect your eyes, because shorting the cap/ spark gap runing will radiate much UV and intense light (acute retinite danger).
RESULTS: 60 cm sparks measured between two horisontal points, even up to 65 cm for angled discharges (but they were not measured).
Anyway, the system has to be very well ballanced. Too much input voltage and the flyback would start to saturate. Too low BPS and the sparks would not fully develop. Too high BPS and the cap would not charge completely. Too small spark gap and the cap would not charge at the maximum possible voltage. With such weak source (flyback), you have to tincker a bit.
So what can we do more?
1. Higher Q secondary (smaller inductance secondaries but with lower ohmic resistence)? Because the BPS will be still low, we have to increase the cap energy. That will require big primary cap, so more secondary impedance to match. Not much space to play with.
2. Bigger topload- trying to get the maximum topload capacitance for a given setup, for the maximum spark output - have to experiment
3. Very big secondaries but with lower ohmic resistence (thick wire)- maibe considering a distributed Ls and Cs (twin or magnifier-like setup). Why not? But I dont think I would achieve much more with the same input energy.
Philer proved his skills with 73 +/- 1 cm cm sparks from a ZVS driven flyback powered SGTC
His setup:
Secondary: diameter = 16 cm, wound lenght = 64 cm, N = 1500 turns with 0.42 mm magnet wire
Toroid: 16 x 60 cm
Primary: cone type angled at 5 degrees, inner diameter = 24 cm, N = 12 turns, taped at 11 turns
Primary cap: MMC type 66 nF
Simple gap
The TC devil bits again....
I rebuilt the last setup with a new flat primary (easier to tune) and a bigger topload. I observed that for my many turns secondary high BPS (lower Cp) simply doesn't turn well. So I tryed to get the maximum with a bigger cap.
SECONDARY
- the same secondary from "Step twelwe"
TOPLOAD
- stacked toroids: little (8.75 pF), medium (11.77 pF) and a big 11/57 cm one
PRIMARY
- 30 cm diameter glass base
- outer diameter = 51.5 cm
- inner diameter = 30 cm
- N = 10+3/4 turns, taped at 9 turns, 4 mm bare copper wire
1 cm interturn distance, 2 cm above the glass base
- total calculated inductance (at outer turn) = 92.79 microH
PRIMARY CAP
- 250 nF @ 12 kV
SPARK GAP
- single 4 mm gap, BPS = 1-10
First try: 76 +/- 1 cm spark
FINAL RESULT: 80 CM SPARKS
With some primary modifications Philer got 85 cm sparks. This is a good raison to move further.
SETUP MODIFICATIONS
- bigger primary cap: 294 nF @ 10.2 kV - MMC with 17 caps 5 uF @ 600 V in serie (a bit overvolted, I know)
- because severe pri-sec breakdowns I had to rise the secondary a bit (1 cm)
- primary taped at 8 turns
- simple 4 mm gap, firing at a very low rate (BPS = 1-5)
RESULTS: almost 89 cm sparks (this is just a rare event, I had a good one spark from 36 photo shots).
