Making a Faraday cage- anyone done it?

[CaptTom]

Have any of you been to a museum (like the Boston Museum of Science) with a giant Van De Graaffe Generator and lightning show?

The performer is in a Faraday cage. There's no fine mesh. The openings between the bars are pretty wide. The "lightning" hits the outside of the metal bars and runs down the surface of the bars to ground. I'm no expert, but my understanding is that the metal bars are a better path (less resistance) than air, or even the human inside. It's hard to see in this image, but that bolt is hitting the outside of the cage, while the performer is placing her hand close to the bars on the inside.

[Nicholson58]

A faraday cage does not need to be a complete closure. If so, this guy’s face is in trouble.

https://m.youtube.com/watch?v=U3XAIwEZpTg

Free Electrons do not like each other. They will naturally get as far from one another as possible. The electrons in a conductor flow largely along the circumference. This is why providing a path around works. A car, even with windows is a perfectly good alternate path as is an aircraft to protect isolated contents.

It is simply not practical to uninstall, bag and hide your critical navigation stuff, including auto pilot, rate compass, GPS antenna, chargers, alternators, sending units, etc.

The theory is that your rig and copper foil grid throughout your hull approximates a faraday cage by forming a surrounding path outside of the contents and to the grounding plates. It you are in a marina in a storm you can help by additionally grounding this system to a metal piling. Try battery clips. I think this is especially helpful in fresh water where your ground plate is less effective

The fuzzies and other snake oil is supposed to bleed off charge and create an aura at the mast head to encourage the strike to find another path on the other guy’s boat.

When there is a strike, you could get:
A direct hit which can be massive and anything can happen
A touch by a lightening bolt leader, not the main bolt
A strike nearby

All three of these will induce voltage and stray currents in the wires of your boat. The first two can feed high voltage directly to bad places.

We have been struck three times while in the Great Lakes, Michigan. The last hit was witnessed by crew on a charter fishing boat nearby in our marina. It was early predawn hours. This one lit up the inside of the boat and jumped to four other boats. My closest dock mate lost his charger-inverter. Everyone lost equipment.

In this hit we lost:
One of three alternators. Diodes destroyed.
Watchmate AIS
Standard Horizon VHF
CD Stereo
18 glass BUSS fuses
60 amp main shore power breaker
Simrad auto pilot computer
3 of 6 LED deck lights
Aqua Signal Tower LED lights
Mizzen mast anchor light
Deck level nav lights
All bow cabin wiring was fused
Many LED cabin lights
Hull Paint damage around the engine through hulls
Raymarine ST 60 instruments
The Windex wind vane was totally annihilated. Bits of melted metal on deck.

In this strike, the Simrad navigation plotter, compass, radar, depth plotter were untouched. Due to installation needs, these were installed with separate two pole local switches. The switches were installed adjacent to each device so that OFF disconnected both + and - wire connections. The unpowered wires were short.

My hypothesis is that disconnecting the neutral wire eliminates the possibility of induced power on the boat’s neutral leg from reaching the electronics. Pulling the breaker on the positive wire removes power but leaves another long wire prone to an induced voltage spike. In addition, modern electronics OFF switch is a software device. The device is more hibernating than truly off. When the induced voltage spike happens, it blows past the on/off rectifier power control circuit. I opened and inspected the VHS and found elements on the first board burned, cracked, popped.

The lesson applied now is that all of my permanently installed electronics are fitted with a two pole switch that creates an air gap in both positive and negative wires as close as possible to the device. We also unplug antennas and pull breakers. There is a 32 pin plug at the foot of the mast to break all mast wiring. This is about as close to putting electronics on the galley table as possible and it can be done in minutes.

[CaptTom]

Originally Posted by Nicholson58

The lesson applied now is that all of my permanently installed electronics are fitted with a two pole switch that creates an air gap in both positive and negative wires as close as possible to the device. We also unplug antennas and pull breakers. There is a 32 pin plug at the foot of the mast to break all mast wiring. This is about as close to putting electronics on the galley table as possible and it can be done in minutes.

This makes a ton of sense. Of course the real damage is from the surge. Either induced voltage from a length of wire (such as the ground) or directly from a strike. That "air gap" on both wires is cheap insurance. Of course a direct strike can bridge the gap inside a small switch, but at some point nothing you do can prevent damage from voltage that high.

[ShoreFun]

When current flows along a conductor it flows on the outside.

The larger diameter wires are often hollow to reduce weight.

When you have lightning you have huge charged field in the air like a few thousand volt different across say 1 foot of air (I do not know the actual values). So chips could have a large voltage just across the chip even if it is disconnected. This can cause various issues later.

So here is something to think about....

When you get hit by lightning regular lead acid type batteries seem to survive, am I correct (I am not 100% on this). So even though you may not have various pieces of electronics you still have electricity to do something.

The Lithium batteries that are direct replacements are not just batteries. They have some electronics to handle the charging under the cover. Each Lithium cell must be charge independently and something has to decide to supply electricity or allow a charge.

So how good are these batteries in continuing working after a hit?
What do you do if all you have are these batteries?

[Nicholson58]

Originally Posted by CaptTom

This makes a ton of sense. Of course the real damage is from the surge. Either induced voltage from a length of wire (such as the ground) or directly from a strike. That "air gap" on both wires is cheap insurance. Of course a direct strike can bridge the gap inside a small switch, but at some point nothing you do can prevent damage from voltage that high.

As I noted, all nav and chart plotter survived the big one. Never any guarantees.

[a64pilot]

Originally Posted by CaptTom

Have any of you been to a museum (like the Boston Museum of Science) with a giant Van De Graaffe Generator and lightning show?

The performer is in a Faraday cage. There's no fine mesh. The openings between the bars are pretty wide. The "lightning" hits the outside of the metal bars and runs down the surface of the bars to ground. I'm no expert, but my understanding is that the metal bars are a better path (less resistance) than air, or even the human inside. It's hard to see in this image, but that bolt is hitting the outside of the cage, while the performer is placing her hand close to the bars on the inside.

If you look at the picture, you’ll see the arc goes through the Faraday cage to the Woman, meaning of course it’s not effective.
It’s incredibly high voltage but I’d suppose low amperage is why it doesn’t kill her, or she is brave and is holding an insulated conductor in new hand?

[Nicholson58]

Originally Posted by a64pilot

If you look at the picture, you’ll see the arc goes through the Faraday cage to the Woman, meaning of course it’s not effective.
It’s incredibly high voltage but I’d suppose low amperage is why it doesn’t kill her, or she is brave and is holding an insulated conductor in new hand?

This is a theatrical stunt. The supposed faraday cage is not. She is wearing the suit in fine mesh.

Also, high volts, low amps. We had a comedian physics teacher in high school who hung a copper toilet float on monofilament from the ceiling near the door to the room. Hanging below was a sign in clear large letters, DON’T TOUCH. He had a generator in the back, similar to those in the photo. He used it to recharge the float anytime someone touched it. No injuries, just a lot of expletives. Teacher’s name was Zock.

[Lepke]

I got hit in a commercial fishing boat in the 1970s. I had a lightning rod, a copper path to a grounding plate on the hull. Other a static snap on the radio and a big bang, I didn't know lightning had struck the boat until someone called to see how we were doing. It didn't damage any of the electronics of the day including the tube marine radio tied to the grounding plate.
Since then I haven't worried about lightning, since it doesn't hit twice.

[callistov42]

I just keep an old hand held GPS in a small metal box with a piece of rubber mat under it in my nav station. Never tested it but always thought it would serve the purpose.

[a64pilot]

As a kid I used to play with very high voltages using a neon sign transformer.
Even low amps the arc can have significant heat to it, so it can burn.

But anyway if your worried about lightning taking out the electrics, get a Sextant, that takes care of Nav and it’s unlikely it will take out a starter but may take out the switches, but a spare starter will cover that base.
It’s not like lightning flows around a boat like water taking out anything with a wire. So long as hand held devices aren’t connected to the boats electric system they will survive.
I doubt most devices are damaged from direct electrical overload from a strike, I think it’s most likely EMP that destroys devices.

Surprisingly or not, but plain ole kitchen aluminum foil wrapping is a very effective means of protecting from EMP. Now enough power can get through anything, but wrapping a handheld device with a couple layers of aluminum foil is easy and cheap, and effective

[redneckrob]

Originally Posted by David M

Lightning has so much voltage that it might just blow through any cage. I would call any cage lightning resistant but not lightning proof. Remember that lightning has enough voltage to arc across miles of sky.

It's jumping through the air because there is a charge imbalance on either side and the air, poor conductor that it is, is the best conductor available to level the charge at that point. If you have a faraday cage you have an excellent conductor around your items that the electricity will travel through, at which point it will not move to again traveling through air instead to connect 2 sides of the cage internally. I can see why we like to think of lightning like a dart or bullet that "shoots through" anything in it's path given what we see when it strikes, but that mental shortcut doesn't hold with what the electrons actually do in the case that a strike hits a faraday cage. A faraday cage is indeed lightning proof for items inside.

[sailone3032]

i have always wrapped items in aluminium foil. never had a problem

[Kita]

I have seen lighting that did NOT strike a boat but hit the water aft & between kinda two boats at the marina that was caught on security footage that destroyed all the electronics on both boats with just the EM pulse... I guess the point is you don't need a direct strike to create damage

[Redline452]

Originally Posted by Lepke

Since then I haven't worried about lightning, since it doesn't hit twice.

... but the boat would have to be in exactly the same spot on the water in order to be protected!

On the other hand, if you are correct: I bought my boat pre-struck, so the previous owner dealt with the excitement and equipment replacements. ;-)

[mako]

Originally Posted by a64pilot

Surprisingly or not, but plain ole kitchen aluminum foil wrapping is a very effective means of protecting from EMP.

And it makes a great hat... keeps the government from reading my mind!