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How to get gigantic currents from lighning

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Microwatt

Mon Jul 30 2012, 03:33AM

Registered Member #3282 Joined: Wed Oct 06 2010, 05:01PM
Location:
Posts: 224

lets make a reverse tesla coil. don't step up voltage. step it down.build a tank capacitor from huge sheets of aluminum flashing 4 meters apart spark gap set at 1 meter , using these big drain pipes wind cheap copper core sparkplug wire around these big drain pipes. make about 50 feet tall.
the secondary coil will be a casted copper or aluminum coil 6 inches diameter with about 20 turns.

Tetris

Mon Jul 30 2012, 03:59AM

Registered Member #4016 Joined: Thu Jul 21 2011, 01:52AM
Location: Gainesville, FL
Posts: 660

Good luck funding a project like that, that is just theory and unsure whether it would work or not :D

Sigurthr

Mon Jul 30 2012, 01:28PM

Registered Member #4463 Joined: Wed Apr 18 2012, 08:08AM
Location: MI's Upper Peninsula
Posts: 597

I think you left out an important part of the problem: how to harvest lightning and not get killed.

Anyway, it isn't very feasible, and I have no idea if your theoretical circuit would even work. Moreso, I'm not even sure why you need a spark gap in there. It would be more realistic/feasible to use a lightning strike guide system (basically a rocket with a tethered conductor) which is set to charge a capacitor bank. Good luck funding/making a cap bank which can survive multi-megavolt pulses and have enough capacitance to store enough power to be worth doing rocket launches. Even then, you would have to wait for proper weather conditions.

Lightning isn't used as a power source already because it isn't practical to do so.

Steve Conner

Mon Jul 30 2012, 02:08PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Lightning already has gigantic currents!

I don't think the plan would work, as the capacitance of the thundercloud would detune the coil. Or maybe the lightning current would just blow it to pieces.

If it were me I would try to persuade lightning to strike an explosive flux compression generator, arranged so that the strike detonated the charge as well as providing the seed current.

Mattski

Mon Jul 30 2012, 05:08PM

Registered Member #1792 Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527

What about a charge pump? Mostly these are for increasing voltage (i.e. Marx generator) but you can run it in reverse and charge some pulse-rated capacitors in series and discharge in parallel with the right electronics.

The problem is figuring out how to get a lightning bolt to break down air and hit the capacitor stack but not have the stack itself break down. Maybe a big sphere/toroid at the top with a lightning rod pointing upward would be workable.

Antonio

Mon Jul 30 2012, 09:46PM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

Some considerations to see where the idea fails:
The total charge transferred in a lightning strike is not so high. About 100 coulombs at most. Supposing possible to store this charge in a capacitor charged to, say, 100 MV, the collected energy amounts to 0.5*C*V^2 = 0.5*Q*V = 10000 MJ. The required capacitance is Q/V = 1 uF.
A large spherical terminal capable of sustaining 100 MV shall have a radius of at least 33.3 meters. Its capacitance would be 111 pF/m*33.3 m = 3.7 nF. So, you need 270 of these to complete 1 uF, possibly arranged as a large circle. Expensive but possible.
The problem is then to build the inverted Tesla transformer. Supposing insulation good enough for 1 MV/m, the primary coil shall have at least 100 m of length. With 1 meter of diameter and a total of 100000 turns (10000 or less turns leads to an impossible primary), the primary inductance is ~100 H.
The secondary circuit to reduce the voltage to, say, 100 kV, would have 100/1000^2= 100 uH.
Ignoring the small self-capacitance of the primary coil (1.1 nF), the secondary capacitance would be of 1e-6*1000^2 = 1 F.
So, these are the parameters of the inverted Tesla coil:
C1 = 1 uF, 100 MV
L1 = 100 H, 100 MV
C2 = 1 F, 100 kV (!)
L2 = 100 uH, 100 kV
Resonance at 15.9 Hz
Maximum primary voltage: 100 MV
Maximum secondary voltage: 100 kV
Maximum primary current: 10 kA
Maximum secondary current: 10 MA
Conclusion: The primary circuit is expensive but can be built. The secondary circuit is difficult, due to the large capacitance and huge current, but is not impossible to build as a large capacitor array.

Microwatt

Mon Jul 30 2012, 11:32PM

Registered Member #3282 Joined: Wed Oct 06 2010, 05:01PM
Location:
Posts: 224

this idea does not fail

here are the stats
tank capacitor 73 pf
primary inductance .8H
secondary windings 5500
secondary windings 20

primary current 10kA
primary voltage 10MV

secondary voltage 50kv
secondary amperage 20000A
resonant frequency 30KHZ

you assume that the capacitor must store the entire charge of the lightning strike.

maybe you can paint a giant weather balloon with graphite for your terminal.

Tetris

Tue Jul 31 2012, 12:12AM

Registered Member #4016 Joined: Thu Jul 21 2011, 01:52AM
Location: Gainesville, FL
Posts: 660

Lightning can be anywhere from 200kA to a megamp. That's kinda scary O.o but AWESOME. How on earth you'd harness that kind of power, I don't know. But then again, harnessing the power is impractical. Would be one fricken awesome science experiment, also expensive, but not really that practical. Now I may not know much about high voltage, but I do know about lightning, and lightning lasts for five milliseconds, and the energy in joules delivered won't be that much, unless you managed to get hold to a superbolt. (will add to this later)

Microwatt

Tue Jul 31 2012, 04:49AM

Registered Member #3282 Joined: Wed Oct 06 2010, 05:01PM
Location:
Posts: 224

why not store it in a gigantic inductor made from scrap iron, aboveground pool and a ton of wire.

Forty

Tue Jul 31 2012, 07:08PM

Registered Member #3888 Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649

I've often thought a rail gun directly powered by lightning would be pretty epic and slightly feasible.

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