harnessing lightning, or not

My Maxwell capacitors hard at work energy from harnessing lightning, see my post with photo, at the CR4 forum.

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 Thanks,
    - Win
Reply to
Winfield Hill
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You rate 3 "good" answers out of 14. That site has very high standards!

Why not use the lightning to heat water? The impedance match is potentially better, and it's easy to store hot water. We could throw a neighborhood hot-tub party after every strike, every 40 years or so.

We don't get lightning here. I kind of miss it.

John

Reply to
John Larkin

Yes indeed! My lightning answer, complete with photo and calculations, is not yet a "good answer" because it didn't get enough votes. Hmm, it did get one vote, was that from you John? Thanks!

Aren't there serious problems with developing a high electric field in water? I mean, above about 1V it wants to break apart into H2 and O. And what about the electrode double layers?

I dunno, it'd need to be a tall 1MV / 100kA = 10-ohm resistor with water cooling, or something. But if rated at a puny 1MV, it wouldn't warm up much water, with only 1MJ of energy. Sigh.

Yes.

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 Thanks,
    - Win
Reply to
Winfield Hill

If it can make it from way up there all the way down to way down here, it can certainly make it across any dielectric inside any cap, so you guys are poking holes in the insulator layers to beat the band, in your caps..

A cap to store SOME lightning strike energy would be about a 300' x

300' (or more) insulator plate of Delrin or Teflon, or an even thinner plate of GLASS. The storage plate would have to be completely encapsulated.

One ends up with a large, flat form factor Leyden jar.

Reply to
BlindBaby

post

lightning sounds like a good way to destroy some otherwise really expensive and fun to play with capacitors. Plus, if you think you can get those made for only $5000 each, you're in for a surprise.

Anyways, go for the quarter shrinker, it's lots of fun.

I'd try to of your caps in series, center tap grounded.

be very wary of hysteresis when shorting out those caps too. the residual energy stored in them is quite unsafe and "builds" rather quickly. I use multiple pieces of solid 12 guage wire across my energy storage caps, just to make sure. There's really no room for mistakes with such monsters.

Even if you're a cowboy and don't care about safety, consider the next person that touches them by accident after cleaning up your mess.

Lastly, the 50uS lightning strike number is pretty meaningless, as that won't be the timing if you're trying to charge hundreds of thousands of uF of capacitor before they fail and short out.

Reply to
Cydrome Leader

post

An illustration of how ugly numbers destroys a beautiful idea!

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http://www.transcendence.me.uk/ - Transcendence UK
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Reply to
Dirk Bruere at NeoPax

post

Visit Central Florida in a month or so. We have storms with over

1000 strikes in a half hour.
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Reply to
Michael A. Terrell

Do the math on that, please.

John

Reply to
John Larkin

No, sorry, I didn't register to vote. In fact, I don't register to vote on anything, ever. I don't want to decide anything about other peoples' lives.

I guess a little of the energy would go into dissolution. The fact is, a lightning pulse is so short, with such a risetime, it will be hard to steer into any load.

Yup. Lightning is all show.

In New Orleans, you could sit on the Lake Pontchartrain levee and watch massive thunderstorm fronts sweep in, with beautiful and noisy lightning. It was usually warm rain and made warm puddles, so you could sit there and get wet and really experience things.

Here we get pretty dramatic fog shows, some compensation.

John

Reply to
John Larkin

Lightning: Smallest bolts are like 6MV. They drop down from a mile in the sky. They can surely make it across ANY two terminal device you think you can come up with. Unless you are separating the nodes by over a mile.

My cap would flash over as well, but more would remain stored than in any of the scenarios discussed here thus far.

No math required.

Reply to
Archimedes' Lever

Win,

For short (a few usec or shorter) pulses, water is actually a very good dielectric. Because of its high permittivity (~80), water is often used as the dielectric material in high voltage, low impedance transmission lines and interim capacitive storage units used in high-energy pulsed power systems, such as Sandia's ZR machine. The shorter the pulse width, the greater the peak voltage that can be supported across a water gap. An empirical relationship was developed by J. C. Martin under a uniform E-field over a range of voltages, pulse times, and electrode area based upon his work at Sandia:

F = k*(t^(-1/3))*(A^(-1/10))

where: F = the peak breakdown field (in MV/cm) t = duration of applied voltage (in microseconds) A = area (in square cm) k = 0.3 for water (positive streamers ? the normal case) k = 0.6 for water (a special case where field enhancement is purposely adjusted to cause streamers to form preferentially from the negative electrode instead of the positive electrode)

For example, positive streamer breakdown field (F) for a pair of 100 square-cm electrodes in water, stressed by a 1 microsecond pulse should withstand a field of ~189 kV/cm. If we used a 100 nsec pulse, this increases to ~408 kV/cm, and to ~879 kV/cm for a 10 nsec pulse. YMMV - media degassing (or outright pressurization) is essential to prevent premature breakdown.

Considerably more detail can be found in "High Power Switching" by Ihor M. Vitkovitsky, ISBN-10 0442290675, ?Introduction to High Power Pulse Technology? by S. T. Pai and Qi Zhang, ISBN-10 9810217145, and "High-Voltage Electrical Breakdown of Water" by M. Kristiansen and L Hatfield, ISBN-10 1934939005.

Breakdown behavior changes with longer (>10 microsecond) pulses, since ionic conduction begins to alter the E-field distribution within the gap. Metallic salts are often intentionally added to water to create high power/high voltage aqueous dummy load and divider resistors for pulsed power work. The electrolyte and end terminal materials must be compatible for long-term stability. Some excellent on-line information sources include a 5 page report from R. E. Beverly III & Associates and a large (147 page) report from Sandia.

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Let me know when you want to begin using that cap to do some serious EM metal-forming/con shrinking... :^)

Bert

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Reply to
Bert Hickman

I doubt that. Show us some numbers. Like Win did.

Hand waving. What you mean is that you can't do math. Which means you can't design electronics.

John

Reply to
John Larkin

If lightning comes down here from a half mile up, it can certainly span the distance between the nodes of any cap you can name, unless it gets made as I described, with its nodes parted by vast distances. Again, no friggin numbers needed.

And I did mention numbers. 6MV and up. Duration doesn't matter. What matters is that the cap's insulative layer survives the charge event without a plate to plate breach.

A huge, flat, encapsulated charge plate, placed flat against the Earth plate will charge up, and hold charge, even after some flash over.

The closer the charge plate can be placed to the Earth plate, the higher the final charge will be, IF and AS LONG AS there is ZERO punch through on the insulator.

Since glass is the best, a thin glass plane mated to the charge plate, and then encapsulated except for an in/out node is all that is needed. The other plate is tied to Earth. The math is the plate area, and the plate separation. The same math used for capacitance calculation the whole time. If we can get the plate closer without a breach, the capacitance of the assembly will grow.

I am not sure, but I am unaware that Maxwell, RIFA or anyone else is making any 6MV caps, much less a 20MV one, which is what we would need to catch a 6 to 10 MV strike.

So the goal must then be to KEEP whatever we can of a failed capture.

That would be whatever remains in the cap AFTER the strike and flash over events pass.

Ideally, we would need a top plate encapsulating the charge plate of about a 2 mile diameter with the node at the center, to actually "catch the whole bolt". Again, if it can jump down here from way up there, then we need a top plate at least as big as the gap is between down here and up there.

Since we will never get a cap that big, my flash over scenario is all we are left with.

That is, IF you want to actually capture the voltage levels of the lightning,as well as the energy sent. Anybody can take a strike on any cap and have it charge to its voltage.

Show me a cap than can take any lightning hit, and actually be charged to the voltage that the strike was sent at.

Now, does my football field sized cap sound better?

A knowledgeable man would be able to weigh these principals and discuss them, without much mention of math to any great degree at all.

Reply to
Archimedes' Lever

You are wrong again, John.

And it is quite funny that this is the only 'hand' you have to wave.

It is also quite telling, however, that you wave it without any real foundation whatsoever.

Reply to
Archimedes' Lever

Hilarious. Engineering is all about the math.

John

Reply to
John Larkin

What were these Maxwell capacitors originally built for?

Reply to
Greegor

Engineering conceptualization, however, is not.

Just ask A. Garrett Lisi.

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What he ended up with is as mathematical as it can possibly get, yet how he conceived of it was not.

You lose... again.

Reply to
Archimedes' Lever

Probably laser pulsers. There are only a handful of applications for them.

Reply to
Archimedes' Lever

I'm not going to write a treatise about it, but that's not right. The entire 100MV or whatever isn't instantly available across any spot along the path; instead it has to follow the rules of physics (and electronics). We can analyze what happens in a small region.

First, it has a current waveform that rises rapidly, but not too rapidly, to the peak current. This causes a voltage drop across the local path inductance, V = L dI/dt. I say the current rises not too rapidly, which is good for a carefully-designed setup, but at up to say 20kA/us, it's certainly rapid enough to cause mayhem elsewhere. Say there's a modest 1uH of wiring inductance, oops, that's a 20kV drop, lasting 5us or more, long enough to create a new discharge and a new undesired pathway for the continuing 100kA lightning current. My capacitors have 40nH of inductance, limiting voltage spikes from this part of the pulse to a manageable 800V.

Then there's the current charging the capacitance. As calculated, 200uF is enough to limit the net voltage rise to 10kV over the 25 to 50us of 50 to 100kA stroke current. During the event, there's a dV/dt = i/C of up to 500V/us on the capacitor, which again, is well under the Maxwell's rating. It's meant to be discharged in as little as 6.6 us, a shorter time than we're considering here. Under that condition its specified design life is 10,000 cycles.

So, no, I don't expect the cap to flash over. Bring it on!

--
 Thanks,
    - Win
Reply to
Winfield Hill

All sorts of high-energy pulsed-power applications. Typically, banks of HV metal-cased energy-discharge capacitors are used to supply 10's to

1000's of kilojoules at 100's of kA - MA levels. Common examples include pulsed magnetizers to charge rare-earth magnets, industrial electromagnetic metal forming (and coin shrinking), laser flash tube pulsers, Pulse Forming Networks (PFN's) for driving klystrons in RF particle accelerators, kicker magnets to redirect the particle beam in the same. Other areas include mundane cable "thumpers" to locate short circuits in underground HV power cables, to reactive armor on tanks to create a pulsed magnetic field to disrupt the supersonic copper metal jet used in armor-piercing weapons, and EM weaponry such as rail guns or electrothermal launchers. Basically wherever you want MW - TW of instantaneous power on tap...

Bert

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Reply to
Bert Hickman

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