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Old 12-11-2020, 19:59   #46
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Re: Lightning Protection for Electronics

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So why do witches burn?
There are ways to tell if she's a witch!
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Old 13-11-2020, 01:14   #47
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Re: Lightning Protection for Electronics

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So why do witches burn?
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There are ways to tell if she's a witch!
Witches only burn if they are made of the type of wood that floats or if they turn you into a Newt.
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Old 13-11-2020, 03:18   #48
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Re: Lightning Protection for Electronics

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Originally Posted by NPCampbell View Post
All electricity travels on the outside of a conductor ... except lightning...
If we believe in a single flowing "electricity," we will have little grasp of basic electrical science (which is all I have).
An electric current is a very slow flow of charges, while energy flows fast. During AC alternating current, the charges move slightly back and forth, while the energy moves rapidly forward.
NP is talking about alternating current “skin effect”, which depends on the frequency, where skin effect increases as the frequency increases.

At normal household AC (50/60hz) the skin depth is about 8-10mm, but at microwave frequencies the depth of the metal, that the current flows in, is about the same as a wavelength of visible light.

The variation of the magnetic permeability (Lorentz force) of the conductor, as well as hysteresis effects, will make the variation of the resistance with frequency even more complex.
DC current, however, travels through the bulk cross section of the wire.
All this is way too complicated, for my simple understanding.
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Old 13-11-2020, 04:21   #49
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Re: Lightning Protection for Electronics

I think of a lightning strike like an old camera strobe. The kind where you'd hear the whine of the circuit charging the capacitor until it is ready to fire.
If you have a lightning suppression system, it is as if you are grounding that flash capacitor so that its charge never gets high enough to arc across the flash tube.

The suppression systems bleed off the charges reducing need or chance for a strike in your area. Property and equipment under the "cone of protection" are at a lower potential than out side the cone since the suppression system is carrying the charges around or above the structures. If a strike is going to happen, it should happen where the voltage difference is the highest since the energy in that difference is what causes the electron flow to start. Nature is trying to normalize the charges.

A ship with a wooden mast does nothing to bleed off the charges. Since the wood is an electrical insulator, up to a point, there is no cone of protection. The mast is electrically neutral, not helping or hurting your chances. The boat is as likely to suffer a strike as anywhere in the surrounding area. It should just be chance.

Trees get hit all the time. I would say that it is random chance but I have tulip trees on my property and do find that they are hit at a disproportionately high rate. It seems to bugger my understanding of how this works.
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Old 13-11-2020, 08:39   #50
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Re: Lightning Protection for Electronics

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Originally Posted by StoneCrab View Post
If you have a lightning suppression system, it is as if you are grounding that flash capacitor so that its charge never gets high enough to arc across the flash tube.

The suppression systems bleed off the charges reducing need or chance for a strike in your area. Property and equipment under the "cone of protection" are at a lower potential than out side the cone since the suppression system is carrying the charges around or above the structures. If a strike is going to happen, it should happen where the voltage difference is the highest since the energy in that difference is what causes the electron flow to start. Nature is trying to normalize the charges.

A ship with a wooden mast does nothing to bleed off the charges. Since the wood is an electrical insulator, up to a point, there is no cone of protection. The mast is electrically neutral, not helping or hurting your chances. The boat is as likely to suffer a strike as anywhere in the surrounding area. It should just be chance.

That makes sense. Thanks for the explanation!
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Old 13-11-2020, 09:01   #51
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Re: Lightning Protection for Electronics

Quote:
Originally Posted by StoneCrab View Post
I think of a lightning strike like an old camera strobe. The kind where you'd hear the whine of the circuit charging the capacitor until it is ready to fire.
If you have a lightning suppression system, it is as if you are grounding that flash capacitor so that its charge never gets high enough to arc across the flash tube.

The suppression systems bleed off the charges reducing need or chance for a strike in your area. Property and equipment under the "cone of protection" are at a lower potential than out side the cone since the suppression system is carrying the charges around or above the structures. If a strike is going to happen, it should happen where the voltage difference is the highest since the energy in that difference is what causes the electron flow to start. Nature is trying to normalize the charges.

A ship with a wooden mast does nothing to bleed off the charges. Since the wood is an electrical insulator, up to a point, there is no cone of protection. The mast is electrically neutral, not helping or hurting your chances. The boat is as likely to suffer a strike as anywhere in the surrounding area. It should just be chance.

Trees get hit all the time. I would say that it is random chance but I have tulip trees on my property and do find that they are hit at a disproportionately high rate. It seems to bugger my understanding of how this works.
Living, growing trees are filled with water. The water includes whatever ionic compounds are dissolved in the groundwater the tree feeds from.
Maybe your tulip trees are far softer (more open cells filled with water) than other trees on your property, and so conduct electricity somewhat better.
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Old 13-11-2020, 09:36   #52
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Re: Lightning Protection for Electronics

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Living, growing trees are filled with water. The water includes whatever ionic compounds are dissolved in the groundwater the tree feeds from.
Maybe your tulip trees are far softer (more open cells filled with water) than other trees on your property, and so conduct electricity somewhat better.
That is a good point, and raises a few questions. We have read a few comments from those who have been struck by lightening. Of those, who had metal masts and have any had wooden masts? The follow on question is what was the rigging made of and were there any antenna cables run to the top of the mast?

Is there a statistically significant difference in the rate of strikes between metal masts and wood masts? Are there enough wooden masted boats to get a large enough sample size?
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Old 13-11-2020, 11:13   #53
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Re: Lightning Protection for Electronics

Quote:
Originally Posted by StoneCrab View Post
I think of a lightning strike like an old camera strobe. The kind where you'd hear the whine of the circuit charging the capacitor until it is ready to fire.
If you have a lightning suppression system, it is as if you are grounding that flash capacitor so that its charge never gets high enough to arc across the flash tube.
The suppression systems '[Don't] bleed off the charges reducing need or chance for a strike in your area...
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That makes sense. Thanks for the explanation!
Unfortunately, it's entirely wrong.
See, for instance this thread ➥ https://www.cruisersforum.com/forums...ml#post1828277
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Old 13-11-2020, 11:43   #54
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Re: Lightning Protection for Electronics

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If we believe in a single flowing "electricity," we will have little grasp of basic electrical science (which is all I have).
An electric current is a very slow flow of charges, while energy flows fast. During AC alternating current, the charges move slightly back and forth, while the energy moves rapidly forward.
NP is talking about alternating current “skin effect”, which depends on the frequency, where skin effect increases as the frequency increases.

At normal household AC (50/60hz) the skin depth is about 8-10mm, but at microwave frequencies the depth of the metal, that the current flows in, is about the same as a wavelength of visible light.

The variation of the magnetic permeability (Lorentz force) of the conductor, as well as hysteresis effects, will make the variation of the resistance with frequency even more complex.
DC current, however, travels through the bulk cross section of the wire.
All this is way too complicated, for my simple understanding.
This is a good description of skin effect for steady state AC and DC electricity.

However, lightning is neither. It's a cross between an impulse function and an inverse saw tooth wave that never reaches steady state therefore the field is always changing. Since lightning takes 1-2 microseconds to reach it's peak, I'm assuming it mimics frequencies in the high KHz range.

Since lightning is not "AC" does it have a "skin effect"? Yes, because skin effect is not caused by AC per se, it's caused by any change in field. For example, when applying a 0-100V square wave to a copper conductor, the sharp rise of the square wave behaves like an AC circuit, the field changes rapidly and the current travels on the outside of the conductor. Within a couple of milliseconds (assuming a low freq square wave), the transients from the current spike dissipate, the field normalizes and the constant current at the top of the square wave dominates at which time current density approaches uniformity in the conductor.

However, since lightning occurs within microseconds, rather than milliseconds, it never reaches steady state and the current travels almost entirely on the outside of the conductor.

Should you use really thick wire due to this effect? No, the same problems that you have with high frequency AC you have with lightning. Since the current travels on the outside, it's not worth paying for a thick conductor because the interior of the wire is underutilized. Maybe a solid core helps as a temporary heat sink ... I dunno. I am guessing a hollow conductor is the optimal shape.
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Old 13-11-2020, 11:59   #55
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Re: Lightning Protection for Electronics

Trying to treat a square wave as a DC signal that turns off-on isn't correct in the example. A square-wave is usually analyzed as a series of sine waves including the fundamental (lowest) frequency (f) plus an infinite number of odd harmonics (so, 3*f, 5*f, ....). A saw-toothed wave just includes the even harmonics. So any changing voltage can be analyzed as a series of sine waves. Google Fourier analysis)
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Old 13-11-2020, 12:53   #56
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Re: Lightning Protection for Electronics

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Trying to treat a square wave as a DC signal that turns off-on isn't correct in the example. A square-wave is usually analyzed as a series of sine waves including the fundamental (lowest) frequency (f) plus an infinite number of odd harmonics (so, 3*f, 5*f, ....). A saw-toothed wave just includes the even harmonics. So any changing voltage can be analyzed as a series of sine waves. Google Fourier analysis)
A square wave, sawtooth, impulse function or anything with a point of discontinuity is represented in the frequency domain by an infinite series of decaying impulse functions. What of it? The point is that the skin effect is not due to an AC current, it's due to a fluctuating field, AC or otherwise.
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Old 13-11-2020, 13:17   #57
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Re: Lightning Protection for Electronics

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Unfortunately, it's entirely wrong.
See, for instance this thread ➥ https://www.cruisersforum.com/forums...ml#post1828277
Thank you for this link. It was pretty interesting and informative. Your post number 42 with the links to various studies and papers was exceptionally interesting. Thanks again.
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Old 15-11-2020, 04:16   #58
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Re: Lightning Protection for Electronics

As I read most of the comments/inputs to this thread it is about best practices in lightening protection in general for a sailboat and it's 12VDC system(s).


A direct hit will damage regardless of precautions, but destructive damages due atmospheric charges in the area might be reduced or avoided with the recommended precautions outlined.


Has anyone experience with additional surge protection based on Gas Discharge Tubes (GDTs) and/or Transient Voltage Suppressor diodes (TVS) as used in telephone copper lines as lightening protection?


If so, how and where to implement them, at each vulnerable equipment DC input or elsewhere in the 12VDC circuitry?
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Old 15-11-2020, 06:52   #59
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Re: Lightning Protection for Electronics

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Pantaenius have already indicated that their lightning excess is 30%, unless an endorsed lightning protection system is installed. I can see other insurance companies following suit.
Interesting, thankfully Pantaenius hasn't changed my UK policy which was renewed last month.

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Old 15-11-2020, 07:12   #60
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Re: Lightning Protection for Electronics

" how and where to implement them, at each vulnerable equipment DC input or elsewhere in the 12VDC"

I used a gas discharge tube on the TV coax, and one is built into the VHF antenna switch. For the low frequency/ 12V DC stuff I used a parallel combination of SPDs (surge protection diode) and varistors. If you make this stuff yourself it is so inexpensive you can go overboard. I lost count of all the different places i put them. Always downstream of overcurrent protection, and always in a metal box.

Since I added the surge protection (big electronics upgrade 4 years back), plenty of nearby lightning but still nothing close enough to toss you out of your bunk.

There are some pictures in my albums if you want to see more details. It ain't hard and you can customize the configuration for the particular situation.

Over the many years fooling with boats in Florida I have lost a lot of electrical and electronics to nearby strikes (got Xantrex Freedom IC stacked up), experienced corona discharges from my grounded aluminum outriggers, my wife shocked leaning against the bow rail on our Boston Whaler, one toss you out of the bed Oak tree hit. Everything I own always has been and will be well grounded (house and boats).


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