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Old 26-11-2020, 13:35   #1
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Protecting a pelican case from lightning

Paranoid sailor here trying to ensure plenty of redundant GPS systems.

I am going to put a handheld GPS in a pelican case with sealed bags to separate the primary lithium batteries and handheld.



In an attempt to get BETTER lightning protection. Do I

A. Use anti static foam, cover the case in foil and ground it. OR
B. Use electrical insulating foam, stash it away from any metal and go for maximum isolation.
C. Screw it, lightning is the destroyer of all electronics.
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Old 26-11-2020, 13:45   #2
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Re: Protecting a pelican case from lightning

Not (A). Anti-static foam is a poor conductor. It is meant to bleed off static charge and that can occur slowly so there is no need for it to be a good conductor. Wrapping the inside or outside of the case with aluminum foil could act as a Faraday cage and may be helpful but connecting it to ground would be a big NO as that would tend to make it a desirable path for lightning to follow.

(B) is an OK plan. Lightning is looking for an easy path from it's strike point(s) to ground. The plastic pelican case itself is not an attractive path component. Keeping the case away from metal or other conductors further helps make the case an unattractive part of a conduction path.

Your goal is to keep the lightning conduction path away from your electronics. The best strategy is to keep them inside a full enclosure of conductive material and to have that container isolated from other conductors. Hard wired electronics are in danger during a strike as the boat's wiring will carry the lightning current to them as part of the conduction path or as induced currents and resultant high voltages. Handheld electronics can be relatively safe if stored appropriately. It is just like people. You don't expect everybody on board to die just because the boat was hit. On the other hand if you are hugging the mast during the storm you are in trouble.
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Old 26-11-2020, 13:51   #3
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Re: Protecting a pelican case from lightning

Thanks Doug,

Yea I agree with all your points.

Sorry I confused Anti-static foam with conductive foam. My first idea was maximum grounding.

After reading a bit online. My plan now is to put tin tape on the inside of the box for faraday cage, then store it isolated from everything else. Maybe under the V-Berth.
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Old 26-11-2020, 13:59   #4
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Re: Protecting a pelican case from lightning

Not that it is a best practice but we have a pair of tablets with Navionics and OpenCPN on them for backup navigation. We just leave them in our bookcase. If we get in to a really heavy lightning storm we will put one in the oven, which common wisdom says is a decent Faraday cage. I don't know how true that is but with one in there and one separately on the bookcase, plus a couple phones with GPS somewhere on the boat and paper charts it seems like plenty of backup to me.
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Old 27-11-2020, 09:35   #5
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Re: Protecting a pelican case from lightning

You can buy a faraday cage bookbag type storage off the internet. The wife got me one. $30 USD
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Old 27-11-2020, 10:26   #6
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Re: Protecting a pelican case from lightning

An interesting topic that is only peripherally addressed. We have had a portable GPS in a steel milk powder can for years wrapped in foam and stored, not grounded. We also detach all the electronics we can, including the HF tuner and everything that will fit goes into the oven if TCs threaten. However in a now 25 year circumnavigation we have never been hit although we have spent much time doing refits and maintenance in Florida, the lightning capital of the world and now in the Rio Dulce for the second time. Our home is a steel Colvin Gazelle.

I have often thought we should have made a dedicated Faraday cage by lining a cupboard with copper screen but have never got around to doing so. It would have been so easy as we have a special cupboard that housed a small desk top computer and screen and the HF radio.

Why OEMs do not do so is a mystery to me.

Jim sv Gaia
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Old 27-11-2020, 10:57   #7
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Re: Protecting a pelican case from lightning

Quote:
Originally Posted by jack4566 View Post
Thanks Doug,

Yea I agree with all your points.

Sorry I confused Anti-static foam with conductive foam. My first idea was maximum grounding.

After reading a bit online. My plan now is to put tin tape on the inside of the box for faraday cage, then store it isolated from everything else. Maybe under the V-Berth.
I don't think you will have a Faraday's cage without a ground.
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Old 27-11-2020, 11:02   #8
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Re: Protecting a pelican case from lightning

I have a small (unplugged) microwave that lives in the oven when not in use. I keep a hand held GPS and a small hand crank ssb/weather/am/fm radio and a hand held VHF in the Mwave in the oven.
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Old 27-11-2020, 11:17   #9
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Re: Protecting a pelican case from lightning

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Originally Posted by Cadence View Post
I don't think you will have a Faraday's cage without a ground.
My understanding is that a motor vehicle will keep occupants safe from lightning as it acts as a Faraday cage, it is isolated from ground by 4 rubber tyres...
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Old 27-11-2020, 11:33   #10
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Re: Protecting a pelican case from lightning

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My understanding is that a motor vehicle will keep occupants safe from lightning as it acts as a Faraday cage, it is isolated from ground by 4 rubber tyres...
I can attest to that, My pickup was hit and I'm still here. I would guess is jumped to the wet pavement. Wiped the truck wiring out with hipot shorts. so the body wasn't total protection. I believe you would be better off with a metal grounded case and the GPS raped in a good dielectric.
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Old 27-11-2020, 11:44   #11
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Re: Protecting a pelican case from lightning

When we encounter a thunderstorm, we put our handheld electronics into our metal cooking pots and put the (metal) lid on top.
Grounding is not required to obtain a Faraday's cage. Aircraft in flight are not grounded and are frequently hit by lightning. All metal aircraft usually do not suffer harm from lightning.
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Old 27-11-2020, 13:51   #12
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Re: Protecting a pelican case from lightning

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Originally Posted by Suliwar View Post
When we encounter a thunderstorm, we put our handheld electronics into our metal cooking pots and put the (metal) lid on top.
Grounding is not required to obtain a Faraday's cage. Aircraft in flight are not grounded and are frequently hit by lightning. All metal aircraft usually do not suffer harm from lightning.
I would think all planes are experiencing is a corona since there is no close ground as apposed to boats and autos which have, maybe not the desired path unless one is provided.

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Old 27-11-2020, 14:03   #13
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Re: Protecting a pelican case from lightning

As I understand copper is not the right material for a Farady cage. Copper is not magnetic which I have read is part of the protection. Not 100% certain but steel I think is best.
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Old 27-11-2020, 15:33   #14
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Re: Protecting a pelican case from lightning

A faraday cage is is a uniformly conductive shell. Not important for it to be made from high permeability material (magnetizable) but it is important to have no long non-conductive openings. External grounding of the cage is irrelevant.

It operates by causing a zero electric field inside itself when the cage is subjected to an electric field (such as nearby lightning strike), protecting the contents from conductive currents or high electric field damage.
Yes, I have a degree in this stuff.
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Old 27-11-2020, 16:40   #15
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Re: Protecting a pelican case from lightning

See Maxwell's four equations. It's all there.
AND, don't forget to take the stuff out of the oven after the storm. Cooked electronics could be seriously embarrassing.
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