Subject: Lightning
Date: 30 Jun 99

Ron, I also found some interesting data under a different spelling of the word.  
In fact I found the opposite or earth to be positive and the sky to be negative 
see NASA's drawing in their on-line primer see bottom of page at: 
http://thunder.msfc.nasa.gov/primer/primer2.html

However, most of the electromagnetic energy from lightning is in the very lowest 
part of the radio spectrum, from 0.1 to 10 kHz. The peak of the spectrum 
generally seems to be between 1 and 10 KHz. 

Above 10KHz, the energy spectrum tails off, but has the nature of random noise - 
there are random peaks occurring with short durations.

Note: The following link shows a + and - of about 80 k Amp current at the bottom 
of the page.  See
http://128.252.223.112/posts/archives/nov98/912136278.Ph.r.html

http://roselott.gsfc.nasa.gov/people/valdivia/thesis/node2.html#SECTION011100000
00000000000

NASA has an interesting link that show the ground a positive and the clouds as 
negative. See Figure 1.2: A cloud-to-ground lightning discharge. It starts with 
the stepped leader propagating down. Before the stepped discharge reaches the 
ground, a second discharge of the opposite charge starts from the ground. The 
two discharges meet shorting the circuit and a return stroke is formed which 
propagates upward lowering the charge. This picture is taken from Uman 1987.

Note also the duration times listed.

This next link has some general technical information. 
http://thunder.msfc.nasa.gov/primer/primer3.html

During fair weather, a potential difference of 200,000 to 500,000 Volts exists 
between the Earth's surface and the ionosphere, with a fair weather current of 
about 2x10-12 amperes/meter2. It is widely believed that this potential 
difference is due to the world-wide distribution of thunderstorms. 

Present measurements indicate that an average of almost 1 ampere of current 
flows into the stratosphere during the active phase of a typical thunderstorm. 
Therefore, to maintain the fair weather global electric current flowing to the 
surface, one to two thousand thunderstorms must be active at any given time. 
While present theory suggests that thunderstorms are responsible for the 
ionospheric potential and atmospheric current for fair weather, the details are 
not fully understood.

Typically, more than 2,000 thunderstorms are active throughout the world at a 
given moment, producing on the order of 100 flashes per second.
http://thunder.msfc.nasa.gov/primer/primer4.html

Other interesting links:

"Science Myths"
http://www.eskimo.com/~billb/miscon/miscon.html

This type of item may be useful for our radio equipment.
Gas Discharge Lightning/Surge Protector (BNC) ($19)
http://www.grove-ent.com/LAR1B.html

 ------------------- 
Subject: Lightning surge battery charger idea to test
Sent: 27 Jun 99

Ron Darby wrote:
> 
> This setup
> will almost always produce a static electrical charge, but under normal
> conditions the current available from this static charge is miniscule
> (mainly because of leakage within the capacitor).   It's only when
> thunderstorms are present ... even tens of miles away ... that the static
> charge becomes great enough to "leak" through the air and produce useable
> current from the capacitor.

Based on Darrell Olson's idea about bridge rectifier, and capacitor filter - I 
couldn't stop thinking about how one might design a circuit to capture static 
electrical surges that occur during lighting storms.  Ron I agree with your 
analysis as described above.  Been thinking how to take some of the danger of 
component destruction and personal risk out of it and still harvest the surges 
to charge batteries.  Still only those who fully understand and respect the 
dangers involved should do this testing. 

If one has a lot of lightning going on, one might try the following circuit. 
http://home1.gte.net/ob/LIGHTNING.gif It would work best if one has lots of 
windmills or high posts.  At the top of each, one would put up a lighting rod 
with a wire down to a spark gap and a good ground connection.  Each lightning 
antenna would be wired to making the shortest path to ground through the spark 
gap for each high point or post.  Extremely heavy gauge wire would be used for 
this.  

The spark gap would be kept out of the rain and should be adjusted to about 1/8 
inch or closer.  The gap could be as simple as a heavy gauge wire wound around 
each end of a glass insulator.  Wire ends then bent to make the proper spaced 
gap.  The gap could be made more formally out of a half inch (or bigger) cadmium 
plated steel or brass bolt threaded through an angle iron bolted to plastic. The 
other side of the gap is a mirror image or use an angle bracket only.  

A smaller wire say 16 to 12 gauge would then be run between the lightning rods 
and the surge limiting inductor near the battery charger as shown.  The battery 
charging area probably should not be located inside the survival quarters or 
near living creatures of any kind. 

The fuse is used in case the DC surge flow gets too high to avoid damaging the 
rectifier in a heavy duty lightning storm.  I recommend making your own fuse.  
Put a couple of terminals in a block of wood or plastic about 6 inches or more 
apart.  The large distance is to attempt to limit the high voltage surges that 
would try to jump this gap after the fuse blows and the storm is not done yet.  
Choose a small wire that will burn out at about half the amperage of the diodes 
and run this wire between the two terminals. To get this wire you can slice open 
a multi-strand wire and separate out the strands. Test one with an amp meter, 
variable resistor and a battery to see what amperage it burns out at.  Use as 
many strands as needed to get the current you need.  Warning don't try to change 
this fuse in the middle of a lightning storm.  

Always short out the spark gap to ground, that is near the fuse, when working on 
this circuit.  This spark gap should be adjusted slightly wider than any of the 
others.  This is to encourage the flow directly to ground near the lightning 
rod. 

For the inductor use one winding on an old transformer (from a TV as an example) 
or wind your own. This is used to limit rapid surges of current to the rectifier 
diodes.  The gas discharge tube (neon or florescent) and 2nd inductor is 
optional protection and visual indication of the presence of high voltage.  Find 
a high current and high peak inverse voltage diodes or bridge rectifier that you 
have available. 

The capacitor is really a bit optional and is used to help level out the surges.  
It should not be leaky and drain the battery while waiting for the next 
lightning storm.  Otherwise it should be as big as you can find. You can make 
one from a plastic (tarp or bag material) between tin foil rolled up. You may 
want to measure the current drain on this circuit from time to time to check 
whether the diodes or capacitor has been damaged.  If this happens your 
batteries could drain down and go dead while waiting for the next storm.

If this approach works for you, battery charging voltage will not a problem. 
It's average current that will be low.  For charging more than one battery, hook 
them in series.  Just don't exceed the voltage of the diodes or the discharge 
lamp. 

This circuit has not yet been tested. If anyone tests it before the PS let the 
rest us know if it produces enough charging current to be worth building.  The 
problem being lightning storms are very short term and sporadic.   Just remember 
lighting is a spectator sport don't go working on this circuit in the presence 
of a storm. 


 ------------------- 

 
