AC Flyback SGTC, calculating MMC capacitance?
Fiddy, Sun Nov 02 2014, 08:48AMG'day,
I plan to build a SGTC with one of my modern AC flybacks.
Im using a bipolar 1000W ZVS from eBay.
With 10 turns on the primary of my flyback im getting a very nice 26.5kHz sinusoidal wave, peaking at 74V.
The secondary of the flyback has 3000 turns and 110ohms of resistance
I can only measure the secondary voltage of the flyback by setting a arc gap up and cant measure the secondary current.
Now how exactly would i impedance match the secondary of the flyback to the tank cap of of the tesla coil?
The normal way would be C = 1/(2 x pi x f x V / I)
Ive made a guess at the secondary voltage and current.
So 1/(2 x pi x 26500 x 22,000 / 20mA) = 5.5pF
5.5pF sounds really small, its small than the top load capacitance of 8" toroid for a secondary?
Is my working out correct? Am i going in the wrong direction?
Any help would be great.
Fiddy.
Re: AC Flyback SGTC, calculating MMC capacitance?
Sulaiman, Sun Nov 02 2014, 11:01AM
short answer ... high frequency ac is not suitable for a sgtc.
You could rectify the output and with an inductive ballast go for resonant charging
but that would defeat the purpose of your ac flybacks.
I would consider a 'magnifier' type TC for which your ac flyback looks ideal,
. find the open circuit resonance frequency of your secondary
(I'm sure potential purchasers will be interrested in this parameter)
. build a TC coil & topload to match this frequency, base drive it from your transformer secondary
. drive the primary at this frequency with an 'interruptor'
I see the main use of your transformer as a source of high frequency high voltage power
to drive a voltage multiplier,
e.g. <= 15kV per stage as that's a common hv rating
Sulaiman, Sun Nov 02 2014, 11:01AM
short answer ... high frequency ac is not suitable for a sgtc.
You could rectify the output and with an inductive ballast go for resonant charging
but that would defeat the purpose of your ac flybacks.
I would consider a 'magnifier' type TC for which your ac flyback looks ideal,
. find the open circuit resonance frequency of your secondary
(I'm sure potential purchasers will be interrested in this parameter)
. build a TC coil & topload to match this frequency, base drive it from your transformer secondary
. drive the primary at this frequency with an 'interruptor'
I see the main use of your transformer as a source of high frequency high voltage power
to drive a voltage multiplier,
e.g. <= 15kV per stage as that's a common hv rating
Re: AC Flyback SGTC, calculating MMC capacitance?
Fiddy, Sun Nov 02 2014, 12:18PM
Why is high frequency AC not suitable? I see many flyback driven tesla coils on youtube...
yes that would defeat the very purpose of these transformers.
Fiddy, Sun Nov 02 2014, 12:18PM
Sulaiman wrote ...
short answer ... high frequency ac is not suitable for a sgtc.
You could rectify the output and with an inductive ballast go for resonant charging
but that would defeat the purpose of your ac flybacks.
I would consider a 'magnifier' type TC for which your ac flyback looks ideal,
. find the open circuit resonance frequency of your secondary
(I'm sure potential purchasers will be interrested in this parameter)
. build a TC coil & topload to match this frequency, base drive it from your transformer secondary
. drive the primary at this frequency with an 'interruptor'
I see the main use of your transformer as a source of high frequency high voltage power
to drive a voltage multiplier,
e.g. <= 15kV per stage as that's a common hv rating
short answer ... high frequency ac is not suitable for a sgtc.
You could rectify the output and with an inductive ballast go for resonant charging
but that would defeat the purpose of your ac flybacks.
I would consider a 'magnifier' type TC for which your ac flyback looks ideal,
. find the open circuit resonance frequency of your secondary
(I'm sure potential purchasers will be interrested in this parameter)
. build a TC coil & topload to match this frequency, base drive it from your transformer secondary
. drive the primary at this frequency with an 'interruptor'
I see the main use of your transformer as a source of high frequency high voltage power
to drive a voltage multiplier,
e.g. <= 15kV per stage as that's a common hv rating
Why is high frequency AC not suitable? I see many flyback driven tesla coils on youtube...
yes that would defeat the very purpose of these transformers.
Re: AC Flyback SGTC, calculating MMC capacitance?
Sulaiman, Sun Nov 02 2014, 12:50PM
Quote: "Why is high frequency AC not suitable? I see many flyback driven tesla coils on youtube..."
Can you point to two ?
then maybe I have missed something ...
Sulaiman, Sun Nov 02 2014, 12:50PM
Quote: "Why is high frequency AC not suitable? I see many flyback driven tesla coils on youtube..."
Can you point to two ?
then maybe I have missed something ...
Re: AC Flyback SGTC, calculating MMC capacitance?
Fiddy, Sun Nov 02 2014, 01:03PM
Certainly
Fiddy, Sun Nov 02 2014, 01:03PM
Certainly
Re: AC Flyback SGTC, calculating MMC capacitance?
Wolfram, Sun Nov 02 2014, 01:58PM
Those are all using DC flybacks.
In an AC-driven Tesla coil, the tank cap should charge and discharge at least once for every AC half-cycle. Any charge left in the capacitor when the supply voltage reverses will just lead to increased losses. At mains frequency, this is fine, as the break rate can easily be higher than the mains frequency. With a power supply operating at tens of kilohertz, this mode of operation is not really practical, there is very little energy in each cycle of the input voltage, so the bang energy would be tiny, and it would be very hard to make a spark gap that could quench at such a high rate.
Wolfram, Sun Nov 02 2014, 01:58PM
Those are all using DC flybacks.
In an AC-driven Tesla coil, the tank cap should charge and discharge at least once for every AC half-cycle. Any charge left in the capacitor when the supply voltage reverses will just lead to increased losses. At mains frequency, this is fine, as the break rate can easily be higher than the mains frequency. With a power supply operating at tens of kilohertz, this mode of operation is not really practical, there is very little energy in each cycle of the input voltage, so the bang energy would be tiny, and it would be very hard to make a spark gap that could quench at such a high rate.
Re: AC Flyback SGTC, calculating MMC capacitance?
Sigurthr, Sun Nov 02 2014, 09:28PM
A magnifier setup would be ideal, but then you couldn't use the ZVS module you're planning to, since they can't be interrupted or precisely frequency driven without painstakingly tuning the zvs. You'd need a half bridge and VCO to drive the AC flyback more easily. This mode also risks over voltage of the AC flyback secondary through resonant rise.
You'd have to rectify the output of the AC flyback to do the normal SGTC circuit. I'd probably use an old EHT diode vacuum tube for the job, but a microwave oven diode string would work too. Or use a DC flyback instead.
You could also make a CWSSTC out of it by driving the AC flyback at the secondary resonance of your TC and using a nonresonant primary. There would be an impedance mismatch but if you use a low impedance primary then it's no more harsh on the transformer than driving a large flaming arc. The tough part would be tuning the ZVS to the TC secondary resonance. This is the safest for the AC flyback though, and the least lossy method. I'd go this route myself.
Sigurthr, Sun Nov 02 2014, 09:28PM
A magnifier setup would be ideal, but then you couldn't use the ZVS module you're planning to, since they can't be interrupted or precisely frequency driven without painstakingly tuning the zvs. You'd need a half bridge and VCO to drive the AC flyback more easily. This mode also risks over voltage of the AC flyback secondary through resonant rise.
You'd have to rectify the output of the AC flyback to do the normal SGTC circuit. I'd probably use an old EHT diode vacuum tube for the job, but a microwave oven diode string would work too. Or use a DC flyback instead.
You could also make a CWSSTC out of it by driving the AC flyback at the secondary resonance of your TC and using a nonresonant primary. There would be an impedance mismatch but if you use a low impedance primary then it's no more harsh on the transformer than driving a large flaming arc. The tough part would be tuning the ZVS to the TC secondary resonance. This is the safest for the AC flyback though, and the least lossy method. I'd go this route myself.
Re: AC Flyback SGTC, calculating MMC capacitance?
Fiddy, Mon Nov 03 2014, 03:37AM
Hmmmm well then, how do i impedance match a mmc to a DC flyback?
Fiddy, Mon Nov 03 2014, 03:37AM
Hmmmm well then, how do i impedance match a mmc to a DC flyback?
Re: AC Flyback SGTC, calculating MMC capacitance?
Ash Small, Fri Nov 07 2014, 02:23PM
This may be of some use:
It will double the voltage, though, which could present some problems
Ash Small, Fri Nov 07 2014, 02:23PM
This may be of some use:
It will double the voltage, though, which could present some problems
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