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My first spark

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Andy

Sun Dec 09 2012, 10:54PM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
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Posts: 874

Its meant to be 20kv, but the diodes were throwing up errors.
I have tried Cockcroft-Walton setup, but the max voltages was at the third stage out of five, the caps were about 400pf would that have been the problem?
What would be a good size for both the setups.

Cheers

Proud Mary

Sun Dec 09 2012, 11:14PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Andy wrote ...

Its meant to be 20kv, but the diodes were throwing up errors.
I have tried Cockcroft-Walton setup, but the max voltages was at the third stage out of five, the caps were about 400pf would that have been the problem?
What would be a good size for both the setups.

Cheers

If you were supplying the C&W with 50 Hz from an NST, (or any other AC power sources at 50 Hz) then the reactance of the capacitor (a kind of resistance to alternating current that capacitors have) will have been almost 8,000,000 ohms, 8 megohms, which we write 8 MÎ©. This is a very high resistance, so only a very small AC current can flow through it. Reactance decreases as frequency increases, which is why C&Ws are usually operated at much higher frequencies, so
much smaller (and less expensive) capacitors can be used.

If we increased the frequency by a thousand times from 50 Hz, to 50 kHz, then the reactance of a 400 pF capacitor would fall to just a tiny bit less than 8,000 ohms, 8 kilo ohms, (which we write 8 kÎ©), so a much larger current could flow through it.

Capacitive reactance is given the symbol Xc - X for reactance, and the little 'c' for capacitance.

The formula for calculating capacitive reactance is Xc = 1 / (2 * Ï€ * f * C) where f is the frequency in Hz, and C is the capacitance in Farads.

Andy

Mon Dec 10 2012, 02:13AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

The diodes in the circuit for one stage makes the voltage go from 20 upto 200, is that a error with the program or for two stages it can go up that much.

edited
Test with a 40kv diode string, after awhile of the sparkgap firing it arced between the first and second diodes about 3cm-4cm. Might need to test 100kv string to see if it works.

Patrick

Mon Dec 10 2012, 02:18AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

So if we want our NST's to live long, happy lives, we should avoid resonant conditions at all costs?

Proud Mary

Mon Dec 10 2012, 12:59PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Andy wrote ...

The diodes in the circuit for one stage makes the voltage go from 20 upto 200, is that a error with the program or for two stages it can go up that much.

edited
Test with a 40kv diode string, after awhile of the sparkgap firing it arced between the first and second diodes about 3cm-4cm. Might need to test 100kv string to see if it works.

I'm afraid I've lost track of what you are trying to do here, Andy. Your circuit diagram is still showing 20V coming from a battery consisting of two cells - i.e. 3V for two fresh alkaline cells.

Here is a tip for learning about circuits: Explain the function of each component and what it does from the moment of switch-on, and ask yourself how the circuit would behave if a particular component was removed, or shorted out.

Andy

Mon Dec 10 2012, 08:06PM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

In the simulator when I close the switch the voltage doesn't increase, but then when I open the switch the voltage shoots up to the breakdown voltage of the diodes, slowly with larger capacitor(small steps at each close). I haven't got the part to test this out, and I'm thinking the simulator isn't working correct.

Proud Mary

Mon Dec 10 2012, 08:15PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Where does the ~450 kV needed to jump your 150 mm gap come from?

Andy

Mon Dec 10 2012, 08:17PM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

100kv sparkgap anyway, based on 15kv 15mm. The circuit?

Proud Mary

Mon Dec 10 2012, 08:28PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Andy, you should be able to make a flow diagram showing what voltage is supposed to be where on each positive and negative half cycle in order to explain what you think the circuit should be doing at any instant of time.

Google voltage doubler and you will quickly find diagrams of this kind, which you will have to understand if you are to make any further progress. Good luck!

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