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Spiral impulse generator = rolled cap Blumlein induction coil!

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LAN_403

Bored Chemist

Thu Apr 24 2008, 05:56PM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

Do you folks know one of you was selling one of these spiral thingies?

Andyman

Thu Apr 24 2008, 07:19PM

Registered Member #1083 Joined: Mon Oct 29 2007, 06:16PM
Location: Upland, California
Posts: 256

Yes, one mil is the same thing as 1 thousandth of an inch or .001 inches. Not millimeter

jpsmith123

Fri Apr 25 2008, 12:44AM

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

I looked into these spiral vector-inversion generators a few years ago. I may be wrong, but I ultimately concluded that for voltage pulses of several hundred Kv to a Mv or so, with pulse widths of tens to hundreds of ns, delivering energies of tens to a few hundred joules, an air-core pulse transformer might be a better all-around choice. Yes, the spiral generator has the apparent advantages (over a Marx generator) of cheap construction, small size and a single spark gap switch, but a properly designed and constructed air-core pulse transformer would have the same advantages, I think, and may actually be easier to build and more robust.

Proud Mary

Fri Apr 25 2008, 10:25AM

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

jpsmith123 wrote ...
a properly designed and constructed air-core pulse transformer would have the same advantages, I think, and may actually be easier to build and more robust.

But for the home experimenter, amateur scientist and tinkerer like me, the Vector Inversion Generator is a whole new challenge with new concepts and new skills to master. You might as well tell a radio ham he could buy a better transmitter than he could ever build, so why waste his time in the garden shed with a soldering iron. But that is not what hobbies are all about!

jpsmith123

Fri Apr 25 2008, 11:11AM

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

I didn't mean to imply that it's not worth tinkering with, if you're so inclined; rather, I was pointing out that if you're building it because you want an inexpensive source of moderately fast HV pulses for some application, an air-core pulse transformer might be better. (And I don't see how your "buying vs building" analogy applies, since you would build the air-core xfrm and in a sense face "a new challenge" there too).

Tesladownunder

Sat Apr 26 2008, 08:42AM

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

Another upgrade with 40% more windings.
Specs
Output... bright 1inch (2.5cm) sparks (perhaps 30kV)
Input..... less than 12kV peak. (ie 3 times voltage stepup) (NST doubled plus 1MOhm).
Foil........ Equal length copper foils 4.5cm x 367cm plus lead in.
Former... 4.2 x 7cm. Ext diameter 8cm.
Turns..... Calculated 20 turns
Spark gap 2mm
Core...... Ferrrite E cores to fit in 4cm gap.
Cap....... 45 nF (prev one was 0.9nF)
Insul...... Polyethylene groundsheet

Arcing over is a problem with higher input voltages and the higher voltage. Anything further would have to be under oil.
I am still a bit uncertain about the 12kV input with voltage doubled NST across the diode and with a series resistor into the capacitance of the generator. It is probably a fair bit lower as the 2mm spark gap is at the limit of working. I will try with a different supply and metering later.

Has anyone else got any spark photos to show?

Peter

Proud Mary

Sat Apr 26 2008, 09:17AM

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

Well done, TDU.

I've sent off by mail order for some aluminium tapes but I haven't sorted out the dielectric yet, which seems to me to be at the heart of the thing.

cedric

Thu Sept 02 2010, 09:24AM

Registered Member #2941 Joined: Fri Jun 25 2010, 08:08AM
Location:
Posts: 143

does any body have measure the rise time of the secondary pulse?

Proud Mary

Thu Sept 02 2010, 07:45PM

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

cedric wrote ...

does any body have measure the rise time of the secondary pulse?

Pulse rise times of well designed vector inversion generators are in the nanosecond regime, but I had no equipment suitable for making these kind of meausrements with the few small VIGs I constructed.

Patrick

Thu Sept 02 2010, 08:08PM

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

Nanosecond rise times are fast, but maybe a well configured CVD with a really good DSO-scope could do it?
If the rise times were 100-200nS im sure it could be done with a specialized set-up. with ferrite i can pretty much say with certainty that the rise times are way slower, so measurement may not be impossible, resistively or capacitivley.

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