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Spiral impulse generator = rolled cap Blumlein induction coil!

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Mates

Mon Apr 21 2008, 03:38PM

Registered Member #1025 Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566

Harry wrote ...

As I understand it, the insulation needs to increase in proportion with the number of turns, which can result in high voltage Vector Inversion Generators becoming physically large.

As I understand the concept, than the demands on the dielectric strength of insulation layer should be constant within the whole coil (why it should increase???). But for higher voltages the oil bath seems to be necessary to prevent the side sparking...

Definitely very interesting conceptâ€¦ I'm already getting a roll of suitable plastic sheet.

BTW: Soldering of aluminum should be possible with special solder material. I've never tried by myself but my friend told me it is piece of cake in case you have the proper solder.

Proud Mary

Mon Apr 21 2008, 05:32PM

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

Mates wrote ...
As I understand the concept, than the demands on the dielectric strength of insulation layer should be constant within the whole coil (why it should increase???).

Doesn't the pulse grow in amplitude as it travels round each succeeding turn of the spiral line? Surely the maximum voltage of the pulse only appears for a moment at the output end of the active line, or have I got something wrong here?

Mates

Mon Apr 21 2008, 06:02PM

Registered Member #1025 Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566

Harry wrote ...

Surely the maximum voltage of the pulse only appears for a moment at the output end of the active line...

Yes, that's the point - the maximum voltage difference will be between the end and the beginning of the stripe. So these two ends are separated by so many layers of insulation how many turns you have... But maybe I'm wrong because it's hard to say what will be the potential difference between the active and passive stripe which are insulated only by one layer all the time ...

Proud Mary

Mon Apr 21 2008, 06:26PM

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

Mates wrote ...

But maybe I'm wrong because it's hard to say what will be the potential difference between the active and passive stripe which are insulated only by one layer all the time ...

I now think perhaps you were right to start with - that the voltage across the end of the active and passive lines will still only be 2V because the relative charge on the passive line will go up as well with each succeeding turn.

Like you, I see this as being a device that would be most reliable under oil. If glass fibre tapes (as used in boat building) were used for the interwinding insulation, then they would saturate with oil and be self-repairing.

Dr. Shark

Mon Apr 21 2008, 09:44PM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

I made another one of these, maybe if I post a few picture of the construction it will help others. I used overhead sheets and kitchen foil, so the construction is slightly less "professional" than Peter's. I started by cutting up MylarÂ® overhead slides into 16 stripes of 5 cm width. Pasting them together gave me a short strip about 50cm long and a long strip of about 4m, which equates to roughly 5 turns and 40 turns. Next I invented a funny way of obtaining a 3cm wide strip of aluminium foil from kitchen foil. These were rolled up per Peters instructions, adding short pieces of copper foil (from a ATX PSU transformer) to give the terminals. The last pic shows the end result with a ferrite core that I intend to use with it.

Now I'll go see whether it works!

Tesladownunder

Mon Apr 21 2008, 11:23PM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

Well, the ferrite improves the performance as far as sparks are concerned. They are more intense and now are out to about 8mm.
It is now possible to use the full voltage input (3kV DC peak = peak of 4kV NST half wave rectified). The air core version performance was best with a small intense spark and got smaller with a bigger voltage input. The ferrite one improves with increasing voltage.

I guess this confirms that there is some induction acting in the setup. I imagine the pulse width has gone up considerably though.

TDU

1208820026 10 FT43795 Hvspiralferrite8mm

Weston

Tue Apr 22 2008, 02:23AM

Registered Member #1316 Joined: Thu Feb 14 2008, 03:35AM
Location: Cambridge, MA
Posts: 365

Like mentioned I used a Coxal cable. I have seemed to have made a mini Tesla coil. I can light up florescent tubes and neon bulbs with out direct electrical contact. I provided the voltage with a flash camera operated voltage multiplier.

Dr. Shark

Tue Apr 22 2008, 08:28AM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

I hate to be the one to criticize this neat idea, but I find the performance of Peter's and my VIG rather disappointing. In the thread here

there is talk of 6 inch sparks, but looking at Peter's pictures his VIG seems to be as weak as mine. Even with the increased number of turns (I have 40) and the ferrite core, there is no discernible boost in performance.

Maybe a better understanding of the device would be in order, as from the papers I have been reading so far there are no hard design guidelines as to what works and what does not.
I don't think there is any "tuning" that can be done with the device, at least there is no resonant frequency to hit, so the best we can do is a clever trade-off of inductance and capacitance in the circuit. This allows tuning the output impedance, but should not affect voltage much.

The variable most deserving of further investigation is probably the turns ratio. Since the "original" Fitch generator had an 1:1 ratio, it may not be such a good idea after all to use a lot more secondary turns. The extra turns don't do any "vector inversion" but just provide transformer action, which may not work so well with the masive inter-turn capacitance. On a more pragmatic level, having more primary (rather than secondary) turns increases the capacitive energy storage, so you get more bang regardless of efficiency.

Proud Mary

Tue Apr 22 2008, 08:46AM

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

Tesladownunder wrote ...

I guess this confirms that there is some induction acting in the setup. I imagine the pulse width has gone up considerably though.

TDU

So far as I can understand it from the various patents for spiral generators with ferrite cores, the ferrite acts by reducing the oscillatory frequency - slowing the decay - on the passive (slow) line, and thereby improving overall voltage and power efficiency.

I also found this interesting statement in the abstract of a paper:

In this paper, we will show that there is a functional relationship between the value of diameter to number of turns ratio (D/n) and the voltage efficiency. This is understandable in the context that for a given diameter, the diameter determines the characteristic "speed" of the "slow" part of the VIG while the length which is directly proportional to the number of turns determines the characteristic "speed" of the fast side. Thus, the D/n ratio is a measure of the ratio of the high/low frequency components of the generator

Characterization and applications of vector inversion generators
Merryman, S.A.; Rose, M.F.; Shotts, Z.
Pulsed Power Conference, 2003. Digest of Technical Papers. PPC-2003. 14th IEEE International
Volume 1, Issue , 15-18 June 2003 Page(s): 249 - 252 Vol.1

Unfortunately, I don't have access to the full text, but the statement suggests the reason why some designs add some extra windings to the active fast line and not the passive slow line.

On a practical note, another patent packs the VIG cores with ferrite rods, which is good for me, as I have a box of 'em.

PORTABLE X-RAY GENERATING MACHINE
United States Patent US3681604

Dr. Shark

Tue Apr 22 2008, 09:37AM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

Harry wrote ...

Unfortunately, I don't have access to the full text, but the statement suggests the reason why some designs add some extra windings to the active fast line and not the passive slow line.

You do now, check your PMs.

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