Author Topic: Need Help w/Build - Lightning Pulse Generator  (Read 801 times)

Offline ElementsnStuff

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Need Help w/Build - Lightning Pulse Generator
« on: February 23, 2021, 07:05:05 PM »
I'm looking to build and/or buy the experimental setup from the attached paper (reproduced below), but I'm not too experienced with building generators like these, so I'm hoping people here have some recommendations on possible existing models that would do the job.



The paper doesn't list models the authors used, and the few statistics it does give don't make much sense to me (then again, I'm not experienced enough to read the entirety of this circuit diagram, only the basic elements like capacitors, inductors and resistors).

Offline MRMILSTAR

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Re: Need Help w/Build - Lightning Pulse Generator
« Reply #1 on: February 23, 2021, 08:57:14 PM »
Just glancing at the schematic this would be a very expensive and difficult device to build not to mention the considerable floor space and logistics such a machine would require. The first thing that I noticed is the motor-generator. The 3-phase AC motor is rated for 350 KW at 6 KV. The DC generator is rated for 300 KW at 700 volts. These are big and expensive machines! They are apparently used to generate high-current continuous DC for melting of the sand. Even if you had this motor-generator or similar, where would you get the power to operate it? Most homes have single-phase 200 amp service at 240 volts. That is "only" 48 KW. Motors of this size also require 3-phase power. Where would you get that?

The capacitors won't be cheap either. These would need to be high voltage pulse-rated capacitors such as made by Maxwell, Aerovox, and others. Then you have the problem of building a high energy reliable triggered spark gap.

Don't forget about the high-power thyratron.

I'm sure that the complexity of this machine is because they are trying to closely emulate the timing and pulse shape of an actual lightning strike while still providing enough energy to actually make a fulgurite.

If you are just interested in making fulgurites yourself without trying to conform to the actual physics and timing of a lightning strike, there are much easier ways. The resulting fulgurites may not look exactly like those produced by a an actual lightning strike but should be good enough for entertainment value if that is your goal.

I attended a Teslathon about 20 years ago where someone brought along a home-made fulgurite machine and made them on demand right there from sand. It was based on fairly long-term resistive heating of the sand and took several minutes to make one. I have a fulgurite made by that machine while I was there. I don't remember the exact construction but it was much simpler than this schematic and operated from standard 240-volt power.
« Last Edit: February 23, 2021, 11:45:15 PM by MRMILSTAR »
Steve White
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Offline ElementsnStuff

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Re: Need Help w/Build - Lightning Pulse Generator
« Reply #2 on: February 23, 2021, 10:11:19 PM »
In that case, how much of this setup do you think I'd actually need to replicate the results of this paper?

(This paper was actually the one I was trying to replicate, wanting synthetic lightning quartz, but their methodology section read 'go see this other paper' instead of... something more helpful).

The main goal is to simulate enough of a high-voltage pulse through the quartz stone to result in high local plasma temperatures and pressure waves that transform alpha-quartz to beta-quartz, resulting in the characteristic lightning-patterned fractures along the surface (like Lichtenberg figures for stone). From what I can tell, this essentially amounts to a single high-voltage, high-current discharge through the piece as it's submerged in sand or other medium, which incidentally results in a fulgurite leading down to the buried quartz crystal.

It might end up being that this visual appearance can be accomplished using a much simpler method, but I wouldn't know off the top of my head what that method is. For now, what would be sufficient to generate a single high-voltage, high-current pulse across a distance of at least one inch (through sand and other insulating materials)?

Offline MRMILSTAR

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Re: Need Help w/Build - Lightning Pulse Generator
« Reply #3 on: February 23, 2021, 10:34:17 PM »
The simplest way that would roughly approximate lightning would be to use one or more large energy discharge capacitors. There are 4 examples on E-Bay right for $400 each with a maximum energy storage of 83 KJ. These weigh around 400 pounds each. This type of capacitor is capable of well over 100,000 amps. I would seed the path through the sand with a fine-gauge strand of copper wire just to establish an initial plasma channel. I don't know if this would be enough energy to melt the sand that quickly but it might. You could probably do some rough thermal computations to determine if ~80 KJ is enough to melt a small quantity of sand in less than about 40 us.  Here is a link to the capacitors if you want to play.

https://www.ebay.com/itm/AeroStor-24-000-VDC-High-Energy-Discharge-Capacitor-by-AEROVOX/133516131634?hash=item1f162e7d32:g:mLkAAOSwUJNfWmTR

You would still need to build a charging circuit which for this particular capacitor could be just a 15 KV NST followed by a full-wave bridge rectifier. You would also need to build a good high-power spark gap switch and some other safety features.

I have built a pulsed power generator with a 24 KJ capacity for shrinking coins, crushing cans, launching disks, and exploding fruit. I've never tried making fulgurites with it. That might be an interesting experiment to try one day. Here is a picture of mine. Anything that you build would probably end up looking somewhat similar depending on your fabrication skills.

It should go without saying that large energy discharge capacitors are very dangerous.
« Last Edit: February 23, 2021, 11:00:07 PM by MRMILSTAR »
Steve White
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Offline AeraCura_

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Re: Need Help w/Build - Lightning Pulse Generator
« Reply #4 on: February 23, 2021, 10:44:25 PM »
Quote
I have built a pulsed power generator for shrinking coins, crushing can, launching disks, and exploding fruit.

A video of shrinking coins. These two hilariously Live Up To Electrical Engineer And Physicist Stereotypes.

Offline ElementsnStuff

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Re: Need Help w/Build - Lightning Pulse Generator
« Reply #5 on: February 24, 2021, 04:40:10 AM »
Would I be right in assuming an appropriate sparkgap switch would be a scaled-up version of this?
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I noticed small 60-100 kV power supplies much like the one seen in the video are fairly cheap (something like $10), but do they hold up to the extra instantaneous current that should be passing through them once the switch is closed by the spark, or should something else be added to protect that voltage supply (is there even a diode that could handle that?)

Also, the spark gap distance itself should be something greater than the dry breakdown distance of around 5mm if I'm charging at 15 kV, correct?

The only other safety features I would add off the top of my head are a redundancy switch before the NST (to make it impossible to fire by accident), some kind of slow-discharge path for the capacitors to make sure they're fully drained (probably another sparkgap of <5mm would do?), and finally a voltmeter on the capacitor side to ensure no overcharging occurs when the NST is active. Are there any others that I should be thinking of?
« Last Edit: February 24, 2021, 04:41:49 AM by ElementsnStuff »

Offline MRMILSTAR

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Re: Need Help w/Build - Lightning Pulse Generator
« Reply #6 on: February 24, 2021, 06:08:12 AM »
What you show in that image is not even close to what you would need. You would need something that can handle many thousands of amps reliably and safely. Here's a picture of the spark gap switch for my pulsed power machine. It is all mechanical relying on bringing the 2 electrodes in close proximity without touching in order to fire. The electrodes consist of 2" diameter 1" thick brass round bar. The conductors are made from 2" x 3/16" copper flat stock. I have used this at up to about 50,000 amps with no problem. I think that it could easily handle at least 100,000 amps and probably more. I would forget about electronic triggering. Its not reliable enough for my level of risk tolerance.

Take a look in the "Capacitor Banks" section of this forum under my name. I published a lot of detailed pictures of my pulsed power generator about a year ago. Here is a link to save you time.

https://highvoltageforum.net/index.php?topic=699.0

This is the sort of construction that you will need to safely work with the energy levels required to do what you want to attempt.
« Last Edit: February 24, 2021, 11:51:31 PM by MRMILSTAR »
Steve White
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Offline Mads Barnkob

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Re: Need Help w/Build - Lightning Pulse Generator
« Reply #7 on: March 03, 2021, 09:45:28 PM »
This reminded me of a old project I saw on 4hv.

A 200kV marx generator discharging into rock samples to separate them into different minerals. It used multiply fast discharges to destroy the samples. He also went through a lot of trouble with exploding chambers and loosing material due to the destructive forces of such discharges in a chamber.

Unfortunately, pictures are long gone broken on 4hv :( https://4hv.org/e107_plugins/forum/forum_viewtopic.php?p=1&id=142691
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Offline johnf

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Re: Need Help w/Build - Lightning Pulse Generator
« Reply #8 on: March 05, 2021, 04:45:37 AM »
We were going to try and make the rock disintegrator at work. "GNS Science"
The marx generator discharge system used a rock in a salt water bath with the preemptive that at high enough voltages the discharge would go the the rock and not the water severing the rock along the grain boundaries. In doing this you can then find the included zircons in the rock and isotopically date the zircon formation to age date when the rock was formed.
Tis a very scary beast and the EMP that it creates has to be managed ie faraday cage. I have a 6kW 150kV spellman supply at the ready for when I find some decent high voltage caps.

This is not a hobbyists plaything. It involves extreme dI/dt and extreme dV/dt both of which are destroyers of just about everything you value

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Re: Need Help w/Build - Lightning Pulse Generator
« Reply #8 on: March 05, 2021, 04:45:37 AM »

 


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