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Old 02-04-2009, 03:47   #1
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Sparks, Wicks, Sticks and Stuff

This thread was sparked (pun intended) by recent threads on lightning and other electrical aspects of boating life. I am hoping it will be a general discussion of electrical principles that some (most - all) of us don't fully understand. In doing so, some of us will learn, some of us will have beliefs disproved and some of us will understand how and why some things work (or don't work).

Please remember I am not a boffin, just a field engineer so don't take what I say as gospel - but if you can't disprove my points, I will retain the right to hold them as true .

To start the ball rolling, let's look at the common electrical spark, you know the one, the flash you get when you short out a battery or blow a fuse. The same one that occurs when using a stick (arc) welder or at the end of a spark plug.

I state 12 volts is not enough volts to create a spark (or even 110 / 220 volts). I know many of you will think of all the times that you had a spark when making a wiring error on your 12 volt system (or you 110 volt system). But you actually had a 1000's of volts before that spark occurred.

Try this, bring two conductors connected to a 12V source very very close together BUT without touching each other - no spark, even if you get within a thousandth of an inch apart.

Why no spark, because dry air is a very good insulator and 12V is not enough potential difference (PD) to ionize the air.

But what was that spark you got when you shorted out your battery terminals, there was 12V available then - wrong. What happened was you actually allowed the two conductors to touch and current flowed. Then you pulled them apart stopping the current flow. Then you got a spark .

Why - the current flow that occurred when the conductors were joined created a electro-magnetic (EM) around the wire. Stopping the current flow causes the EM field to collaspe. This collapsing field around a conductor induces a voltage into the wire (general generator principle - a conductor moving in relation to a conductor or vice versa creates a PD).

If the current was large to begin with (like a short on a battery), the EM field around the wire would be large. It the current was stopped quickly, the rate of change of the collasping field would be large, therefore we have a very large rate of change of a magnetic field cutting a conductor, thus we have induced a large voltage into the conductor as soon as we pulled it away form the other conductor.

The volts induced are in the order of 10,000's at the moment of seperation. It is this voltage that ionizes the small air gap. This ionized air is now a very good conductor and allows a current path to be maintained. This is the spark you see, it is current flow through an ionized air gap. The current will continue to flow while the circuit is maintained.

It will stop when the circuit changes, typically because the battery discharges (goes flat), or the wire melts (conductor is open circuit) or the battery explodes (overheating) or a fuse blows (circuit protection) or somesuch event changes the circuit.

The important part is that 10,000's of volts was required before the air would ionize, become a conductor and allow current flow.

Similar to the spark plug, if you don't a high tension coil or a set of points going open circuit, no spark at the plug.

Now lightning is just a big spark jumping through ionized air between two objects that have a large (very large) PD between them - usually two clouds or a cloud and ground. Yes, I know there is a bit more to the lightning story but this is lightning 101.

We can take the discussion into the realms of static electricity and what happens there but the principles remain the same. This also similar to how neon lights work and similar to vacuum valves in many ways.
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Old 02-04-2009, 04:59   #2
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Quote:
Originally Posted by Watname
... Why no spark, because dry air is a very good insulator and 12V is not enough potential difference (PD) to ionize the air...
Exactly. The dielectric breakdown* voltage for air is roughly 3 Million Volts per Metre (varies with pressure, humidity, and electrode geometry); so you would need about 300,000 30,000 Volts per Centimetre of electrode separation to start an arc in air.

* Electrical breakdown occurs within a gas (or mixture of gases, such as air) when the dielectric strength of the gas(es) is exceeded. Regions of high electrical stress can cause nearby gas to partially ionize and begin conducting.
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Old 02-04-2009, 05:28   #3
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Erhmmm... Gord: a meter has 100 centimeters... so that would make it 30,000V/cm or 3,000V/mm or 300V/0.1mm which is about the closest you can get the wires without the use of optics or the wires touching.

So, now we start talking about Nicolai Tesla and his coils? ;-) I can see this thread leading to sparks flying all over marina's in the world !

cheers,
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Old 02-04-2009, 05:39   #4
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Erhmmm... Gord: a meter has 100 centimeters... so that would make it 30,000V/cm or 3,000V/mm ... Nick.
Right you are Nick (my bad).

Any kind Mod/Admin reading could correct my miss-statement to read: "30,000 Volts per Centimetre" (not 300,000V/cm).
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Old 03-04-2009, 02:34   #5
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Telsa Coils

Quote:
Originally Posted by s/v Jedi View Post
<snip>

So, now we start talking about Nicolai Tesla and his coils? ;-) I can see this thread leading to sparks flying all over marina's in the world !

cheers,
Nick.
OK, Tesla coils it is, I can't do better than direct you to my favourite Tesla Coil site. Tesla_Downunder
If anyone has better examples, I would love to see them.

Maybe we could get someone like this guy to run some experiments with mast head brushes .
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Old 03-04-2009, 08:03   #6
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I've been a closet engineer for most of my life. I built a Tesla Coil for a high school science fair and studied electrical engineering in college. One restless day (my job has no relation to engineering whatsoever) I came across this website:
"Electricity" Misconceptions Spread By Textbooks
If you want to explore Wotname's original question about electrical principles most of us don't understand, this is one of the best resources out there.

Brett
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Old 04-04-2009, 08:34   #7
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I think that anyone interested should read this book: Amazon.com: Tesla: Man Out of Time: Margaret Cheney: Books

ciao!
Nick.
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Old 04-04-2009, 09:31   #8
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Theory versus practice

I think one of the most "polarizing" issues within this subject is in the difference between the theory of dissiaption of potential energy and the practice of technology .

The point that Nick brought up in the other thread was one of theory. I think most here are in violent agreement on the theory part. Regarless of the means used, few disagree that IF the difference in the states of charge is bled off, reduced, or otherwise equalized (a.k.a. dissipated) that the potential is reduced and therefore the chance for arcing is reduced.

The devil is in the details.

Aircraft static wicks are intalled NOT for lighting protection, but for affecting the degree of static build-up on the airframe. This has all to do with interference with electonics, and little or nothing to do specifically with lightening. BIG BUT here; it does support the theory of dissipation ... and nothing more.

Enter lighting and bottle brushes.
The theory being sound, there is not enough science yet to validate a sufficient technical solution for sail boats. This is due to the variables such as air resistance, lighting potential, and finally the lack in R&D money for recreational sailboats compared to that of the aerospace industry. Bottle brush technology remains primitive when compared to that of aerospace sciences.

It may be that the bottle brush dissipator is minimally effective for specific set of conditions, but at least the theory would suggest that it is more effective than that of four leaf clovers and horse shoes over door jams.
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Old 04-04-2009, 10:19   #9
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Some contrary opinions, representing the informed view:

A CRITICAL REVIEW OF NONCONVENTIONAL APPROACHES TO LIGHTNING
PROTECTION
~ BY M. A. UMAN AND V. A. RAKOV
MARTIN A. UMAN, Distinguished Professor: ECE-UF Dr. Martin Uman

http://www.lightningsafety.com/nlsi_lhm/Uman_Rakov.pdf

WAR OF THE LIGHTNING RODS ~ By Abdul M. Mousa, (Ph.D., P.Eng., Fellow IEEE)
http://www.lightningsafetyalliance.c...htning_war.pdf

There Is No Magic To Lightning Protection:
Charge Transfer Systems Do Not Prevent Lightning Strikes
~ William Rison
(Professor of Electrical Engineering, New Mexico Institute of Mining and Technology)

”... The principles of traditional lightning protection are basic — 1) provide preferential strikes point for lightning (an array of conductors higher than the objects being protected), a good grounding system, and conductors between the two to conduct the damaging current from a lightning discharge away from the structure to be protected; and 2) provide appropriate transient protection on power and signal wires entering the structure to protect equipment and personnel from the effects of induced lightning currents ..."
http://www.lightningsafety.com/nlsi_lhm/magic.pdf

Charge Transfer System is Wishful Thinking, Not Science ~ Charles B. Moore*
(Professor Emeritus, Atmospheric Physics, New Mexico Institute of Mining and Technology)

Charge Transfer System is Wishful Thinking, Not Science - National Lightning Safety Institute

*Charles B. Moore is internationally known for his research on the electrical aspects of thunderstorms and volcanoes. He is an expert in many different areas of atmospheric research, including the scientific and political aspects of weather modification, the scientific and practical issues of lightning protection, and the efficacy of different kinds of lightning rods:
Lightning and Thunderstorm Research - Langmuir Laboratory
http://infohost.nmt.edu/mainpage/news/2005/7feb02.html


Fundamentals of Lightning Protection ~ By Richard Kithil, President & CEO, NLSI*
*National Lightning Institute

Fundamentals of Lightning Protection - National Lightning Safety Institute

Evaluation of Early Streamer Emission Air Terminals ~ By Scott D. McIvor, Roy B. Carpenter, Jr., Mark M. Drabkin, Ph.D.
...”CONCLUSIONS: There is limited test data on ESE performance, and no available data substantiates the suppliers’ claims; conversely, the data collected by independent researchers prove otherwise. That is, the ESE performs no better than the conventional Franklin rod.
2. The physics related to the situation, as provided by the atmospherics physics community, demonstrate that the claims made for all of these ESE are wildly exaggerated ...”

http://www.ees-group.co.uk/downloads/ESE%20paper.PDF
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Old 04-04-2009, 12:36   #10
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Electrons can jump from the anode to the cathode (outside of a cell) even in a perfect vacuum. (In a power-consuming device, the anode is positive, and in a power-releasing device, the anode is negative.) Atmospheric air acts as a CONDUCTOR (not insulator) allowing the electrons to jump a greater distance at a given voltage. With enough potential and a close enough distance, air becomes a conductor with a higher than typical resistance.

There actually is a spark if a cathode and anode with a 12 volt electrical potential get close enough together, the electrical potential is so small though that you do not see it. This sparks cause is different from the collapse of an electrical field....but ultimately caused by the same thing, electrical potential.
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Old 05-04-2009, 06:56   #11
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Quote:
Originally Posted by LtBrett View Post
I've been a closet engineer for most of my life. I built a Tesla Coil for a high school science fair and studied electrical engineering in college. One restless day (my job has no relation to engineering whatsoever) I came across this website:
"Electricity" Misconceptions Spread By Textbooks
If you want to explore Wotname's original question about electrical principles most of us don't understand, this is one of the best resources out there.

Brett
Nice site Brett, thanks for posting it.
I have only glanced at some it but it must be right because I agree with what I saw .
Seriously, I will have to read all on when time permits.
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Old 05-04-2009, 07:04   #12
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Quote:
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<snip>. I think most here are in violent agreement on the theory part. Regarless of the means used, few disagree that IF the difference in the states of charge is bled off, reduced, or otherwise equalized (a.k.a. dissipated) that the potential is reduced and therefore the chance for arcing is reduced.
I am not sure we are really in agreement for some of the theory but I can agree that PD is reduced to below the relevant arcing voltage, no arc will occur. This is self evident . But I disagree that the theory supports the view that the mast brush will reduce the PD to any significant degree let alone to a level below the ionization of the surrounding moist air.

Quote:
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<The devil is in the details.
Gotta agree here.
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Old 05-04-2009, 07:42   #13
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Mr Pedantic replies

Quote:
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Electrons can jump from the anode to the cathode (outside of a cell) even in a perfect vacuum. (In a power-consuming device, the anode is positive, and in a power-releasing device, the anode is negative.)
I have to disagree here (on first principles). You simply cannot have even a single electron travelling (jumping) in a perfect vacuum, as soon as any particle is inserted into a perfect vacuum, it is no longer a vacuum as I understand it.
Quote:
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Atmospheric air acts as a CONDUCTOR (not insulator) allowing the electrons to jump a greater distance at a given voltage. With enough potential and a close enough distance, air becomes a conductor with a higher than typical resistance.
Hmm... I think we need to be clear about what is current flow (especially in a fluid). Are you suggesting free electron flow or + & - ions?
Dry air is considered an insulator until it is ionized at which point it is not "air" as such but rather a mixture of nonionized and ionized gases. IIRC, it is oxygen moleclues (O2) than become ionized (possibilly into O and O3) first rather that the more stable nitrogen. Anyone know more about this aspect???

If there is any free electron flow in air, it would (IMO) be so low as not to be measurable and would not consititute electrical current flow in any meaningful sense (agin IMO)

Quote:
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There actually is a spark if a cathode and anode with a 12 volt electrical potential get close enough together, the electrical potential is so small though that you do not see it. This sparks cause is different from the collapse of an electrical field....but ultimately caused by the same thing, electrical potential.
Well I stand corrected in that it is possible to get a spark from 12 volts when the air gap is such that the dielectric breakdown if the air is reduced to 12 volts. From Gord's (& Jedi's) figure's, this will occur around 0.004 millimetres of separation.

However for the rest of us who sparks out a wire, the spark occurs after we shorted the wire and then pulled it away again .
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Old 14-04-2009, 18:41   #14
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In a nut shell.

Wotname -
Sorry to oversimplify, but ... would this be an a accurate one sentence paraphrase for your position?

Bottle brush bristles plus the sea level atmosphere (together) still carry too much resisitance to effectively dissipate the kind of static potential that will build up preceding a lightening event.
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Old 18-04-2009, 22:19   #15
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[QUOTE=Shack;274294Bottle brush bristles plus the sea level atmosphere (together) still carry too much resisitance to effectively dissipate the kind of static potential that will build up preceding a lightening event.[/QUOTE]

I agree but need to repeat that although the brush doesn't prevent lightning from occurring, it seems to provide protection to the mast it is installed on... i.e. the lightning goes elsewhere, like a similar object without brush. It doesn't need to dissipate the charge of the storm, just the part of that charge that crept up the mast and only to a level that other objects are preferred.

ciao!
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