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Marko

Sat Jun 10 2006, 09:08PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

1) try replacing the toroidal electrode with a circular NIB magnet, with a glass disk over the centre.

I guess you'd need a steady flow of current for a 'vortex' effect to occur, not just a cloud of plasma.
Everything would last too short and happen in small area of tube so I don't think magnet would have any effect.

2) replace the ceramic electrode with a thin glass tube.

Tube needs to be porous and watery, in order to gain relatively low ohmic resistance.
It seems that vapour from inside of the tube actually creates plasma. (I guess again)

Glass tube would just shatter when voltage breaks it down, letting the water in.

Terry Fritz

Sun Jun 11 2006, 03:31AM

Registered Member #393 Joined: Tue Apr 18 2006, 12:30AM
Location:
Posts: 297

Hi,

I think I got all the stuff to go visit the big capaitor. I tested it tonight but was still getting 400 amps with the porus ceramic tube and all:

The tube is just 3/8 diameter chalk milled and drilled:

Chalk is very water permiable, easy to machine, very cheap, and easy to get. I have seven of them made so we'll see how it goes...

Cheers,

Terry

HV Enthusiast

Sun Jun 11 2006, 03:40AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Wow, didn't think so many people would take this experiment so seriously! Looks like all kinds of new toys to play with in the last few months (the SISG, ball lightning, etc...)

Good luck and be sure to take some cool pics if you get it working!!!

Marko

Sun Jun 11 2006, 05:20PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

How are you going to stop the water entering the chalk tube?
Bunch of hotglue or something?

Terry Fritz

Mon Jun 12 2006, 06:15AM

Registered Member #393 Joined: Tue Apr 18 2006, 12:30AM
Location:
Posts: 297

Hi,

We gave it a try tonight. Due to time and equipment we were only able to really fire once at 5400V at 60e-6 Farad. It made a big orange flash but no real fireball yet. The chalk tube blew apart but not terribly violently or loud. We were at 875 joules and the water seems to take most of the "bang" out of it.

A strong small ceramic tube could probably survive the shock. We were thinking a ceramic standoff could have the glazing ground off for it. The tube is probably very well sealed at the bottom but still allowed to fill with water. The top of the tube is probably just at the surface of the water. McMaster or Ohmega might have unglazed tubes too.

The magnitude of the flash seemed about what one would expect. If it were 7X more, that would probably be about right to match the pictures and movie of the real one.

So we seemed real close but did not have it quite right yet. The cap bank could go up to 18kJ if it had too in the future.

One real problem is the SISG. If fired perfectly "once" but I never stopped to think what 800+ joules might do to it.

All the IGBTs are shorted. Seems 100X its pulse rating is "too high".

Easy to fix, but that leaves us with no reliable switch for the fireball thing... Don't know how to solve that yet.

Cheers,

Terry

Steve Ward

Mon Jun 12 2006, 07:18AM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

Easy to fix, but that leaves us with no reliable switch for the fireball thing... Don't know how to solve that yet.

You have the tools to make a very nice HV relay type switch. There is nothing wrong with big copper electrodes coming within .01" of eachother and stopping

. My 5kJ quarter shrinker has been using 2" diameter copper end caps as electrodes. The trick is to not let them touch, but get really close. My switch needs at least 1700V to fire, but thats not a real problem. Im all for silicon, but sometimes it just doesnt cut it!

Marko

Mon Jun 12 2006, 08:10AM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

We gave it a try tonight. Due to time and equipment we were only able to really fire once at 5400V at 60e-6 Farad. It made a big orange flash but no real fireball yet. The chalk tube blew apart but not terribly violently or loud. We were at 875 joules and the water seems to take most of the "bang" out of it.

Yeah, I saw it in a pic.
I actually wonder how was there any flash when chalk was filled with water.
I don't know if this was OK:

A glass beaker filled with salt water contains two protruding electrodes, one of which being insulated from the surrounding water by a clay tube.

Flashover from the water enables the current to enter the clay tube, where it causes the water contained there to evaporate.

As I could figure out you shouldn't let the electorde contact water any way, but just let the chalk get wet (and electrode must not be touching it, I guess)

When you fire the cap a big scary arc will form and due to 'jacobs-ladder' effect (and possibly railgun effect) spray outwards like a goop of plasma.

Maybe I'm wrong, maybe you just need more energy, etc. (the text isn't describng the thing well anyway)...

Terry Fritz

Mon Jun 12 2006, 04:24PM

Registered Member #393 Joined: Tue Apr 18 2006, 12:30AM
Location:
Posts: 297

You have the tools to make a very nice HV relay type switch. There is nothing wrong with big copper electrodes coming within .01" of eachother and stopping .

Yes!! That would be fine for this!! Thanks

Bill Beaty also posted earlier info on all this at:

Cheers,

Terry

Marko

Mon Jun 12 2006, 04:35PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Doh, and I get ignored as usual.

Nobody thinks nothing about both electrodes just being under water, shouldn't there be more arcing in the tube?

Terry Fritz

Mon Jun 12 2006, 05:46PM

Registered Member #393 Joined: Tue Apr 18 2006, 12:30AM
Location:
Posts: 297

Hi,

I assume the tube is filled with water. I would think that the discharge would be incredibly loud like a coin crusher and the "explosion" enourmous if it were not for water in the tube absorbing most of the sound and thermal energy of the 6000 joule discharge. I have not read Bill B's post in detail yet to see if it has clues on this. 6000 joules is about twice the energy of a 30-06 rifle. I would think that type of air arc would knock everyone in the room off their feet!!!

Ours was filled with water and given that the tube broke and the amount of energy we were using, the "flash" we got "looked" just right. Not a plasma ball but with 7X the energy the "bang" would be about the same as in the movie.

In water, I must admit things are very "tame". However, we were all far back with ear/eye protection since if it "goes bad" it could go VERY bad!! We sort of dilibertaly played at lower power for now since mistakes get bad at 6000 joles... Many details need to be figured out for sure first.

BTW - Use a plastic bucket not glass. The glass looks cute but not a real good idea... Also water does splash around a bit so cover the HV stuff with plastic sheet. We kept hearing stuff "fizzing" on charging for the second try. That was no doubt water on something HV burning off

Epoxy can hold the electrod in the tube easily but might have to have a bunch ready incase one breaks. I wonder if just "wood" would work fine too...

Cheers,

Terry

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