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Registered Member #54655
Joined: Thu Mar 19 2015, 05:56PM
Location: BC, Canada
Posts: 82
I once built a zvs flyback sgtc running on 36 volts with a single static gap and a 7nf mmc and it produced sparks as long as 5 inches. It had no charging inductor, simply the half wave rectified output of the flyback directly across the spark gap.
Registered Member #8817
Joined: Mon Dec 17 2012, 05:16AM
Location: Australia
Posts: 110
Benjamin wrote ...
I once built a zvs flyback sgtc running on 36 volts with a single static gap and a 7nf mmc and it produced sparks as long as 5 inches. It had no charging inductor, simply the half wave rectified output of the flyback directly across the spark gap.
Registered Member #30656
Joined: Tue Jul 30 2013, 02:40AM
Location: UK
Posts: 208
Another thought:
You're wanting to reduce the effort of building a rotary gap, which is the standard way to do DC resonant charging as it stops the power arcing problem and allows reliable gap operation and power control
Is it a possibility to turn the driver on and off to stop the power arcing etc, and allow for a smaller gap for more reliable triggering? - Set the static gap to break down at the right voltage for dumping the tank cap into the primary - OR trigger the gap somehow - Turn off the flyback driver when the gap fires, possibly using a photodiode to detect the arc? - Turn the flyback on again after a delay (at least long enough for the tank to ring down and the gap to quench) to charge the tank cap up for the next pulse - Can adjust the delay to control the power level.
Just some random musings, never done or looked in detail at any of this myself!
Registered Member #54655
Joined: Thu Mar 19 2015, 05:56PM
Location: BC, Canada
Posts: 82
No sorry, I don't have any pics or videos but I can try to give you the coil specs because it is dismantled now. It had a 2 by 8 inch toroid and a 2 by 7 inch secondary wound with 30 gauge wire. the primary was about 10 turns of 14 gauge solid bare copper wire in a flat pancake with about 3/8 inch between turns. the spark gap was I think three pieces of 3/4 inch copper pipe evenly spaced parallel to each other. I wouldn't bother with a rotary gap or resonant charging for something this low powered, it's simply not necessary. You can get the same results with a static gap. I have a dual mot coil that makes 5 foot sparks with a half wave doubler, no charging reactor, and a high speed async rsg, and the four microwave diodes right across the spark gap haven't died yet!
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
some decades ago I had to stay a few weeks with my wife at her mother's house after the first few days of repairing or scrapping various domestic electrical products I had time to play with a little 7 kV @200 uA inverter module from a laser printer that I'd scrapped, In anticipation I had a 4" x 12" c700 turn coil in the car ...
Improvised rolled caps, spoon spark gap, house wiring primary, aluminium cooking pot topload, no test instruments other than cheap multimeter,
I found that I could easily get c100mm (4") arcs ... with one spark every 3 seconds .. I later estimated the actual dc input power to be c 0.7 W ... 140 mm/W !
for the small SGTCs that I have built it seems that arcs do not grow from spark to spark the output spark length is proportional to topload voltage, determined by spark gap voltage which is in good agreement with John Freau's empirical formula
Registered Member #8817
Joined: Mon Dec 17 2012, 05:16AM
Location: Australia
Posts: 110
Benjamin wrote ...
No sorry, I don't have any pics or videos but I can try to give you the coil specs because it is dismantled now. It had a 2 by 8 inch toroid and a 2 by 7 inch secondary wound with 30 gauge wire. the primary was about 10 turns of 14 gauge solid bare copper wire in a flat pancake with about 3/8 inch between turns. the spark gap was I think three pieces of 3/4 inch copper pipe evenly spaced parallel to each other. I wouldn't bother with a rotary gap or resonant charging for something this low powered, it's simply not necessary. You can get the same results with a static gap. I have a dual mot coil that makes 5 foot sparks with a half wave doubler, no charging reactor, and a high speed async rsg, and the four microwave diodes right across the spark gap haven't died yet!
Interesting, i might just give it a go without the inductor and diodes first and see the results. My secondary is similar but with a 4" toroid and smaller 32AWG wire on the secondary. Thanks for sharing!
Sulaiman wrote ...
some decades ago I had to stay a few weeks with my wife at her mother's house after the first few days of repairing or scrapping various domestic electrical products I had time to play with a little 7 kV @200 uA inverter module from a laser printer that I'd scrapped, In anticipation I had a 4" x 12" c700 turn coil in the car ...
Improvised rolled caps, spoon spark gap, house wiring primary, aluminium cooking pot topload, no test instruments other than cheap multimeter,
I found that I could easily get c100mm (4") arcs ... with one spark every 3 seconds .. I later estimated the actual dc input power to be c 0.7 W ... 140 mm/W !
for the small SGTCs that I have built it seems that arcs do not grow from spark to spark the output spark length is proportional to topload voltage, determined by spark gap voltage which is in good agreement with John Freau's empirical formula
spark length = 1.7" x SQRT(input power) (60 Hz)
Haha thats pretty good for the input power!
So theoretically a bigger toroid would have a higher breakout voltage but would take longer to charge yeah?
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
approximately;
most of the energy stored in the primary capacitor (E = 0.5 x C x V^2) is transfered to the secondary capacitance (coil, topload, extras) so for a given TC, output voltage is (nearly) proportional to input voltage.
So, with re-tuning, if you increase the topload capacitance the voltage (and frequency) reduce, so a large topload may require a breakout point
as the topload capacitance is reduced the voltage increases (for fixed primary capacitance and voltage) when the voltage exceeds about 3 kV per mm radius, breakout occurs
so the topload radius determines breakout voltage and the primary capacitor voltage determines maximum voltage with no breakout,
plus higher frequencies put more strain on the primary capacitor for the same voltage somewhere above 300 kHz the arcs from TCs become more sword-like at higher power.
P.S. programmes like JavaTC are great, but with simple electronics rules plus Wheeler (for inductance) and Medhurst (for capacitance) formulas/tables/graphs you can get a good estimate of expected performance, and a greater understanding of/feel for your coil.
If you connect your inverter directly to the spark gap (no inductor etc.) put a suitably rated resistor of about 10 kOhm in series with the inverter output
Registered Member #8817
Joined: Mon Dec 17 2012, 05:16AM
Location: Australia
Posts: 110
Sulaiman wrote ...
approximately;
most of the energy stored in the primary capacitor (E = 0.5 x C x V^2) is transfered to the secondary capacitance (coil, topload, extras) so for a given TC, output voltage is (nearly) proportional to input voltage.
So, with re-tuning, if you increase the topload capacitance the voltage (and frequency) reduce, so a large topload may require a breakout point
as the topload capacitance is reduced the voltage increases (for fixed primary capacitance and voltage) when the voltage exceeds about 3 kV per mm radius, breakout occurs
so the topload radius determines breakout voltage and the primary capacitor voltage determines maximum voltage with no breakout,
plus higher frequencies put more strain on the primary capacitor for the same voltage somewhere above 300 kHz the arcs from TCs become more sword-like at higher power.
P.S. programmes like JavaTC are great, but with simple electronics rules plus Wheeler (for inductance) and Medhurst (for capacitance) formulas/tables/graphs you can get a good estimate of expected performance, and a greater understanding of/feel for your coil.
If you connect your inverter directly to the spark gap (no inductor etc.) put a suitably rated resistor of about 10 kOhm in series with the inverter output
I see thanks for the information, ive been using javatc for the design of coils for a while now :)
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Building a ZVS Flyback SGTC
