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Old 18-03-2014, 09:39   #31
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Re: Faraday cage for hand held GPS

The problem with tin foil is its current carrying capacity. A very close by lightning strike can induce so much current that the foil may actually melt, I have never seen it but if there is enough current I could see it happening.
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Old 18-03-2014, 09:49   #32
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Re: Faraday cage for hand held GPS

I recall an anecdote that at some point early in the cold war the west was shocked to examine a MIG jet delivered by a defector and learn that many of the aircraft's systems relied on vacuum tubes, where in the west we would use an integrated circuit. The reason for the reliance on such crude electronics was an effort to mitigate EMP damage at a time when the west didn't think it as an issue.
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Old 18-03-2014, 10:03   #33
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Re: Faraday cage for hand held GPS

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Originally Posted by ionic View Post
Electronic circuits are effectively all protected against this type of EM field by nature of the fact that all PCBs have a ground plane that is a reference to ground will then tie out to some common system ground. The caveat in the wikipedia article above is a big If they do and they MAY induce a current. But this is logarithmically small as the distance from the point charge decreases, and does so very quickly.

If your electronics components fail during a lightning strike, the chances of them failing because of the proximity of an electromagnetic wave is incredibly statistically unlikely as opposed to a faulty ground system, separate ground schemes, or some other commonality of that device and a faulty circuit. If faraday cages were effective at all in protecting against lightning strikes...then don't you think some engineers would have some product on the market?

Just because lighting strikes and you have devices fail doesn't mean it was because of an EMP. Yes, very small magnetic fields arise from ESD fields. And yes, you can induce a voltage or current from magnetism. These are basic principles, but the relative magnitude of of a magnetic field is miniscule in an ESD, and naturally occurring non nuclear EMPs of any consequence are pretty rare. When raymarine engineers start pushing out faraday cages to protect from lightning strikes, let me know.
You seem to be making stuff up! There is so much here that is counter to established science and practice that it is not worth refuting your statements.
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Old 18-03-2014, 10:04   #34
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Re: Faraday cage for hand held GPS

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These bags are not all created the same, I think the ones you are looking for are called "conductive grounding bags" and are handy because they are also ziplocks and will keep your stuff dry. Put one bag inside of another and then put them inside a metal box. I think that about as good as it gets. If I recall correctly 3M makes some really neat metalized plastic boxes with foam lining if you want to burn money.

Again, I don't think it's any guaranty, but it's better than nothing. Obviously you don't know when you are going to get hit by lightning so some might consider it prudent to have a back up GPS device protected in this manner.

Yes, I have taken a lightning strike before. It was back in the LORAN days and before cell phones so I can't comment from experience regarding the LEMP effect caused by lighting, which is really just a big electrostatic discharge, which is what the bags are designed to protect against, however a couple of plastic bags seem like cheap insurance to me and should satisfy your wife.

I think this is really good advice. I will look around for such a bags - I'm not sure if they are available here.
Metal box is not a problem, it will be only necessary to solve the problem of the slot.
It should satisfy myself.
And my wife attitude (I joked about it a little) is: when you need to do something, get a proper tool for a start. I think it make sense
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Old 18-03-2014, 10:13   #35
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Re: Faraday cage for hand held GPS

I like the metal tool box. Put your stuff in it and put it somewhere out of the way. Just get one that has the flanges around it that the lid closes over. That should take care of the slot ant problem mentioned.
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Old 18-03-2014, 10:16   #36
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Re: Faraday cage for hand held GPS

Any metal box will work. From "survival" shop to home depot like electric boxes, or metal locking boxes/safes ... some ideas below:
http://www.endtimesreport.com/faraday_cages.html
https://www.google.com/search?q=prot...icial&tbm=shop
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Old 18-03-2014, 10:44   #37
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Re: Faraday cage for hand held GPS

Link to 3M products that use a conductive plastic for the case-

Product Catalog:*3M™ Conductive Containers

Looks like Pelican uses a conductive foam-
Pelican 1510 case with Anti-Static Pick n Pluck foam
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Old 18-03-2014, 14:26   #38
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Re: Faraday cage for hand held GPS

I just guessing that the static protection bags are designed for static discharges that one would encounter while sliding your feet across a rug or rubbing a cat. Perhaps a static discharge that would leap 1/4" gap. Just sayin.

Maybe try 2 layers AL foil, 2 anti-static bags, screen door wire cage, in an ammo box that is placed in the ships safe.

My last boat was steel and I worried about stray currents radiating from the keel stepped mast. I kept a handheld depth sounder and Garmin 76 in anti-static bags in the oven (I don't think there was a window). Fortunately this was never tested.
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Old 18-03-2014, 18:22   #39
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Re: Faraday cage for hand held GPS

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Originally Posted by Delancey View Post
I recall an anecdote that at some point early in the cold war the west was shocked to examine a MIG jet delivered by a defector and learn that many of the aircraft's systems relied on vacuum tubes, where in the west we would use an integrated circuit. The reason for the reliance on such crude electronics was an effort to mitigate EMP damage at a time when the west didn't think it as an issue.
That is the first time I have heard that excuse for their lack of technology.
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Old 18-03-2014, 19:38   #40
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Re: Faraday cage for hand held GPS

The ABYC document on lightning protection, TE-4, is here, http://www.marinesurveyorschool.org/...Protection.pdf

Lots of good information.

Most of the document is how to protect the boat and thus people on board but there is this little tid bit,
Quote:
Protection of Equipment - Wherever possible, electronic equipment should be enclosed in metal cabinets that are connected to the lightning grounding system with a minimum #8 AWG (8.39mm2) conductor. Surge suppression devices should be installed on all wiring entering or leaving electronic equipment.
Sounds like a Faraday cage to me.

Later,
Dan
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Old 18-03-2014, 19:56   #41
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Re: Faraday cage for hand held GPS

I had a lightning strike (or more likely a near strike rather than a direct hit) a few years ago. Every peice of electronics that was outside, or had a component outside (like the VHF and GPS with an external aerial) was destroyed. Everything that was inside and not switched on was fine.

This indicates to me that the aluminium boat did provide some protection.

I think in a severe lighting strike all bets are off. There will be structural damage to the boat and the loss of electronics is a minor issue. For a less severe strike some sort of faraday cage (like an ammunition box) with a spare H/H GPS is a sensible precaution and is quite easy to do.

A waterproof box/bag (with the GPS and spare batteries) inside the metal faraday cage is also a good addition. Water damage is more common than lightning and many of the GPS units that advertise a waterproof construction do not survive much immersion especially with some rough treatment. Be mindful when storing that alkaline batteries often leak.
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Old 18-03-2014, 20:08   #42
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Re: Faraday cage for hand held GPS

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Originally Posted by Delancey View Post
I recall an anecdote that at some point early in the cold war the west was shocked to examine a MIG jet delivered by a defector and learn that many of the aircraft's systems relied on vacuum tubes, where in the west we would use an integrated circuit. The reason for the reliance on such crude electronics was an effort to mitigate EMP damage at a time when the west didn't think it as an issue.

Quote:
Originally Posted by Therapy View Post
That is the first time I have heard that excuse for their lack of technology.
Was it Einstein who, when asked what weapons would be used to fight the next World War, replied

"No idea ... but I'm pretty sure the one after that will be fought with sticks and stones"
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Old 18-03-2014, 21:44   #43
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Re: Faraday cage for hand held GPS

A little light reading...

HowStuffWorks "How Faraday Cages Work"
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Old 19-03-2014, 00:37   #44
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Re: Faraday cage for hand held GPS

My recommendation for a practical Faraday Cage that wont upset the Admiral is a tin of shortbread biscuits. Of course you do need to eat the biscuits to make it work.

Just wrap your handheld GPS or other survival stuff in non-conductive material and put it inside. If the strike is too close, or a direct hit, then the induced electric fields and currents might still overwhelm that cage as Maine Sail attests, despite theory saying it shouldn't happen. But I figure its worth the effort to try.
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Old 19-03-2014, 01:14   #45
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Re: Faraday cage for hand held GPS

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My recommendation for a practical Faraday Cage that wont upset the Admiral is a tin of shortbread biscuits. Of course you do need to eat the biscuits to make it work.

Just wrap your handheld GPS or other survival stuff in non-conductive material and put it inside. If the strike is too close, or a direct hit, then the induced electric fields and currents might still overwhelm that cage as Maine Sail attests, despite theory saying it shouldn't happen. But I figure its worth the effort to try.
Nicely suggested, Insequent,

Now, are Walkers sold in an appropriate tin?

Ann
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