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Spiral impulse generator = rolled cap Blumlein induction coil!

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Proud Mary

Tue Apr 22 2008, 10:12AM

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

Dr. Shark wrote ...

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.

Thank you so much Dr Shark! Its amazing that such a simple device wasn't discovered until the 1960s, and that professional scientists were still trying to explain how it works in this 2003 paper.

I like to have as much understanding as I can before I start on a project, because I've wasted so much time and money in the past on building things which didn't work properly because I didn't understand all the principles involved.

Dr. Shark

Tue Apr 22 2008, 10:26AM

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

Harry, I completely agree with you, especially after I essentially wasted most of last night constructing a bit of a dud. I already edited my above post to reflect my latest ideas, but I'll repeat:
The only reference that claims an improved output with extra secondary turns is the 1984 patent Peter cited in his first post. This looks more like an ordinary transformer to me than a VIG, although the two are of course intimately interrelated. As I understand the VIG, there is a cycle of LC oscillation which reverses the voltage on the capacitor, so the energy has to be stored in the magnetic field as the voltage crosses zero. At this point, a voltage would be induced in the additional turns. Thus the "extended VIG" seems to be quite different from a normal VIG in its operating principle.

All other references I could find about VIGs just use a 1:1 turns ratio, so that is what I will try tonight. Rewinding my VIG is pretty straightforward, so I'll see if that helps and report back.

Proud Mary

Tue Apr 22 2008, 10:55AM

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

Having got the paper thanks to our friend Dr Shark, and seen the information on the D/n ratio in Table 1, I feel able to begin a modest proof of concept model.

I've decided to use 75mm aluminium adhesive tape for the lines, and a double thickness of 100mm adhesive insulating tape as the dielectric, with a bundle of ferrite rods as the core.

I have the ferrite rods, but will have to send off to ebay for the aluminium tape and the extra-wide insulating tape, so won't be able to do anything in a hurry.

I've not made my mind up on the switch, but suppose I will go for a self-igniting spark gap to start with, which should be OK with a 3kV charge voltage from a Bertrand PSU I have to hand. I will charge a reservoir capacitor first, and power the VIG from that after disconnecting the supply, as I see from various patents that the EMP from VIGs can destroy electronic equipment nearby, or to which it is coupled, so it seems to me to need its own separate low Z earth.

jpsmith123

Tue Apr 22 2008, 11:02AM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843

Could someone please send me that paper by Rose et al.? Thanks.

Dago

Tue Apr 22 2008, 12:21PM

Registered Member #538 Joined: Sun Feb 18 2007, 08:33PM
Location: Finland
Posts: 181

I'm interested in the discharge length, does anyone have equipment to measure such short pulses?

Dr. Shark

Tue Apr 22 2008, 01:05PM

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

I would not count on the pulses being that short, after all there is considerable inductance in the circuit from coiling up the transmission line. In the papers I looked at the discharge in in the order of a microsecond, which is not what I would call short.

Proud Mary

Tue Apr 22 2008, 01:32PM

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

"The pulsewidth is equal to 2nt Ï„t where nt is the number of turns and Ï„t is the average one way propagation time for a single turn. If t = 0 represents the closing of the switch, the leading edge of the output pulse is delayed by an amount nt Ï„t which for many applications is unimportant."

Source: Fast risetime spiral pulse generator
United States Patent 4140917

For practical purposes, I would reckon on the real life pulse being perhaps twice as long as the theory.

The pulses are triangular, but they could always be sharpened with a spark gap if necessary.

Tesladownunder

Wed Apr 23 2008, 08:39AM

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

I have built a beefier setup.
Specs
Output... bright 1/2 inch (1.25cm) sparks (perhaps 15kV)
Input..... 2.5kV peak. (ie 6 times voltage stepup) (NST 1/2 wave plus 1MOhm for testing).
Foil........ Equal length copper foils 4.5cm x 243cm plus lead in.
Former... 4.2 x 7cm. Ext diameter 6.2cm.
Turns..... Calculated 14 turns
Spark gap 1mm
Core...... Ferrrite E cores to fit in 4cm gap.
Cap....... 20 nF (prev one was 0.9nF)
Insul...... Polyethylene groundsheet

So a better result with more turns and area.
How long the dielectric lasts is unclear and also what increase in input voltage and power will it tolerate? Probably needs to be in oil for that.

TDU

Proud Mary

Wed Apr 23 2008, 10:04AM

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

Great stuff, TDU.

I have this morning sent off for 75mm adhesive aluminium tape and 100mm insulating tape from ebay suppliers, so I should have a rig of my own to report on in a week or ten days.

I must say how glad I am you dug this up, and gave us all the opportunity to learn something out of the ordinary.

Tesladownunder

Wed Apr 23 2008, 10:38AM

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

It's interesting to go down a new path. I've often wondered about impulse transformers although I guess this is only just one type.
This new version seems to have scaled in spark brightness consistent with 20 times the capacitance and also scaled in output spark length 8mm to 12 mm consistent with the increased turns from 9 to 14. Construction type was similar and dielectric and input voltage were unchanged.
The capacitor holds its charge well and if discharged with a chicken stick giving a reasonable "zap", will give an output spark as well.
I suspect that for high repetition rates, the use of a multiple segment gap would prevent power arcing.
I also suspect from my experience with TEA nitrogen lasers that the spark gap type and position is critical. The use of a gap with two cylindrical electrodes in continuity with each conductor strip and covering the full width should present the lowest inductance.
As it is, I suspect it could be driven much harder than just a few pulses per second, but I am not ready to break it yet.

TDU

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