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Registered Member #1124
Joined: Fri Nov 16 2007, 01:42PM
Location:
Posts: 17
Hi all,
I have bought all equipment necessary since 2009 but due to numerous setbacks I have never proceeded in utilising them until now. I have a 15KV neon transformer, a 0-20MHz function generator, an osciloscope and a 40KV probe for it.
I have built very simple circuits at the time with the 555 timer however this is very different and I am afraid of toasting the equipment!
Function: 1. Primary target frequency 1MHz. 2. I would like to have capacitors charging and discharging at the rate of the pulse generator. 3. The capacitors should charge into the KV. 4. The capacitors should discharge into a spark gap.
Can someone more experienced point me in the right direction or even better help me built an appropriate circuit? The purpose of the generator is to eventually drive a number of projects such as Tesla coils (in a wide range of frequencies) and experiment with 'radiant energy' (as it is generally known).
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
I do not clearly understand your intentions but there are a couple of things that you should be aware of;
. An NST operates at line frequency (50 or 60 Hz) . An NST has a high source impedance (Vsec/Isec) . Transistors that switch at 1 MHz don't (as far as I am aware) handle kilovolts
as above, a little more information is required as to your goals ...
Registered Member #4074
Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335
Correct me if I'm wrong, but I think it would be very difficult to get a spark gap to fire in phase with your signal/pulse generator. A spark gap will fire when there is enough voltage to ionize the gas in between the electrodes, and the voltage required for it to fire will change depending on electrode temperature, air temperature, and the rate that hot gas can be removed (air flow directed through the gap to quench it). And each pulse of the spark gap isn't just a single event with a rising and falling slope; when the capacitor discharges the energy will ring back and forth across the gap, like the return strokes of a lightning strike. This ringing occurs at the natural resonant frequency of the capacitor and the inductance of the wiring (this is how a spark gap Tesla coil is tuned). It will be difficult to build a spark gap that can fire continuously (and reliably) beyond 1-2kHz without forming a constant power arc, as it's more difficult to properly quench a gap as the firing rate increases.
Registered Member #1124
Joined: Fri Nov 16 2007, 01:42PM
Location:
Posts: 17
Basically the generator should be generating a square wave at 1MHz, and this should be regarded as just the clock or timer of the system.
1. The rest of the circuit should check this wave and when it goes to +ve it should allow the capacitors to charge up. 2. Capacitors can take time to charge, so some pretty fast caps are needed capable of HV at RF. 3. Ideally the cap should discharge before the beginning of the next cycle. 4. And of course the cycle starts again.
There are many simple circuits all over the net using 555 timers and mosfets etc. There are even some with capacitors e.g. camera flash. There are some with HF but not KV e.g. 4MHz solid state tesla coils. However I have never seen any circuits in the RF using caps.
The intension is to be able to charge/discharge HV caps based on the clock of the function generator.
Registered Member #1124
Joined: Fri Nov 16 2007, 01:42PM
Location:
Posts: 17
@GrantX You are right about the difficulties regarding the spark gap. I do not know how high a frequency can be reliably achieved - I am aiming at the highest possible value - hopefully in the MHz. I am guessing that there should be a certain distance between the gaps that depends on the setup - fine tuning is required. Hot air should be removed e.g. fan should be used.
Regarding the ringing effect.... I think this is induced when a cap and a coil are used. I think this was the only way HFHV could be achieved at Tesla's time. I am thinking a little differently - of course I am not saying that I am correct in my thinking. If I can generate the sparking on demand at any of these frequencies, then I can have more control and will avoid tuning problems etc. Of course I do not want this specifically for a Tesla coil. Primarily it is to explore HVHF effects that have to do with radiant energy.
Registered Member #4074
Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335
rororo74 wrote ...
@GrantX You are right about the difficulties regarding the spark gap. I do not know how high a frequency can be reliably achieved - I am aiming at the highest possible value - hopefully in the MHz. I am guessing that there should be a certain distance between the gaps that depends on the setup - fine tuning is required. Hot air should be removed e.g. fan should be used.
Regarding the ringing effect.... I think this is induced when a cap and a coil are used. I think this was the only way HFHV could be achieved at Tesla's time. I am thinking a little differently - of course I am not saying that I am correct in my thinking. If I can generate the sparking on demand at any of these frequencies, then I can have more control and will avoid tuning problems etc. Of course I do not want this specifically for a Tesla coil. Primarily it is to explore HVHF effects that have to do with radiant energy.
A coil is just a piece of wire that is wrapped up. Everything has capacitance and inductance and as frequency increases their effects become very noticeable. A capacitor connected directly to a spark gap with extremely short connections will still ring back and forth. The wires connecting the device, and the capacitor's internal connections (and the plates of the capacitor itself) all have inductance, and at 1MHz this will become noticeable. A capacitor sitting by itself without anything connected has its own self-resonant frequency.
The brass static spark gap I used in a Tesla coil would overheat and form a power-arc after only a few minutes, with a 12nF capacitor discharging at around 100-200Hz. This was with only 100-250 VA RMS consumed by the variac and 8kV transformer (at a fairly poor power factor). I was using a high-flow 200mm fan with a PVC duct directing all of the air straight through the electrodes. Spark gaps get very toasty without proper quenching. Look for a nice sized blower capable of moving some serious air and use tungsten electrodes with a reasonably large surface area, if possible.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
I think the clue here is 'radiant energy'. I think any simple circuit designed to produce sparks at these frequencies will require LC tuning, ie a 'Tesla tank' circuit with spark gap, not unlike the primary circuit of an SGTC.
I think this can be done using the NST for power, with resonant charging, or something similar.
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
if you want 1MHZ that is a time scale of 1us and what you are asking is not easy. if you can do it there probably might be a job for you hear at my work for you. I have never seen a spark gap that will work a 1MHz however a large electron tube mat fit the bill for your switch. depending on what your cap size is you will need a lot more power than a NST. What are you trying to do
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Need help for HVHF pulse generator using function generator
