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Old 15-11-2020, 08:05   #61
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Re: Lightning Protection for Electronics

Thanks for your reply Frankly. Interesting!



Where may I find your "There are some pictures in my albums if you want to see more details."?


And why "and always in a metal box."? Protection or heat dissipation?
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Old 15-11-2020, 08:35   #62
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Re: Lightning Protection for Electronics

I think if you click on my handle that will link you to my albums, if not somebody that knows more about the operation will have to help.

When varistors fail, sometimes the failure mode is with a low enough resistance that they conduct current and depending on upstream protection may catch fire (rare but does happen). Hopefully metal box will help contain that type of event. I think some companies actually pack dry sand around varistor arrays.

Diodes on the other hand usually just fail open and gas discharge tubes fail shorted but no current source normally involved so bare is not much risk.

https://www.cruisersforum.com/forums...lbums5734.html

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Old 15-11-2020, 17:21   #63
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Re: Lightning Protection for Electronics

Quote:
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We have a lightning diffuser on top of the mast, lightning struck it a few years ago.
Did it defuse it? Are they not supposed to divert the lightening away from the mast?
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Old 16-11-2020, 08:22   #64
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Re: Lightning Protection for Electronics

A golfing buddy of mine said he carries a one iron in his bag. In a lightning storm, he holds it up high. Because, "not even God can hit a one iron."
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Old 16-11-2020, 08:37   #65
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Re: Lightning Protection for Electronics

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Originally Posted by Rowmance View Post
A golfing buddy of mine said he carries a one iron in his bag. In a lightning storm, he holds it up high. Because, "not even God can hit a one iron."
Lee Trevino?
After he was struck by lightning, at the 1975 Western Open, Lee Trevino was asked by a reporter what he would do if he were out on the course, and it began to storm again. Trevino answered he would take out his 1-iron and point it to the sky, "because not even God can hit a 1-iron."

But my favorite Trevino quote is: “The older I get, the better I used to be!”
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Old 16-11-2020, 08:49   #66
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Re: Lightning Protection for Electronics

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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.

Yes, and no.

200 years of lightening protection show a fairly heavy gauge wire does best because of the high currents.
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Old 16-11-2020, 09:12   #67
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Re: Lightning Protection for Electronics

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Originally Posted by Alistair242 View Post
Did it defuse it? Are they not supposed to divert the lightening away from the mast?

It diffused the $ balance in his checking account, and diverted funds away way from a more useful boat toy.


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Old 16-11-2020, 09:13   #68
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Re: Lightning Protection for Electronics

There is nothing you can do to mitigate the effects of a lightning strike. Nothing.

The only thing you can do is have a good insurance policy. If an insurance underwriter requires some kind of lightning mitigation, I would probably keep shopping.

Don't fool yourself, you can't stop 300 million volts.

Put a handheld VHF, GPS, (and even a PPIRB) in your microwave oven (or equivalent faraday cage) and keep sufficient flood mitigation supplies at hand.
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Old 16-11-2020, 09:19   #69
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Re: Lightning Protection for Electronics

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There is nothing you can do to mitigate the effects of a lightning strike. Nothing.

That is pure uniformed BS.

Lightning protection systems safely conduct strikes from their targets every day all over this planet.


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Old 16-11-2020, 09:26   #70
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Re: Lightning Protection for Electronics

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Originally Posted by Frankly View Post
That is pure uniformed BS.

Lightning protection systems safely conduct strikes from their targets every day all over this planet.


Frankly
Give me a single example of any sailboat anywhere with evidence that it sustained a direct hit and was not damaged intact and I'll consider it. Don't tell me about aircraft or structures on land. I want to know about sailboats.
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Old 16-11-2020, 09:52   #71
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Re: Lightning Protection for Electronics

One thing I found out about lightning, is to have a shorter path to ground than your electronics. One install, they had a long roll of LMR-400 cable, so they left it behind the desk coiled up. The lightning arrestor was on the end and the ground wire went down to a copper rod driven in the ground. The next lightning strike took everything out. Another RF guy came in and ran the antenna line down to the ground, installed the lightning arrestor and ran another line back up to the 2nd floor where the radio was.
He explained that Lightning always takes the shortest path to ground, so his way gave it a direct path to ground, with no electronics along the way. It was still working when I left that location, years later.

So, if your aluminum mast is keel stepped, make sure your keel has a good grounding plate. I would be cautious about encapsulating the ground wire in fiberglass, unless it is a heavy gauge wire since it will get VERY hot with a lightning strike. That will probably blow off the fiberglass encapsulating the wire and exposing everything else to water.
If you have a deck stepped mast, make sure you have a heavy gauge copper conductor running from the terminal (brush) on top of the mast, down to the keel, or other lightning terminal in the water.

Also, Lightning has little respect for insulation. It will hop through the insulation of one conductor to jump to a better ground.
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Old 16-11-2020, 10:08   #72
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Re: Lightning Protection for Electronics

Quote:
Originally Posted by justinfinity View Post
There is nothing you can do to mitigate the effects of a lightning strike. Nothing.

The only thing you can do is have a good insurance policy. If an insurance underwriter requires some kind of lightning mitigation, I would probably keep shopping.

Don't fool yourself, you can't stop 300 million volts.

Put a handheld VHF, GPS, (and even a PPIRB) in your microwave oven (or equivalent faraday cage) and keep sufficient flood mitigation supplies at hand.
This wasn't a problem with wooden ships, with non conductive wooden sticks in the air.

It wasn't a problem with iron ships with steel poles in the air.

It became a problem with plastic boats with metal poles in the air.

The solution?

Have a large conductive, low resistance path to ground from the top of the metal pole to a large surface area conductor in the water.

The problem?

That metal pole is covered with sensitive electronic sensors, and a radio antenna.

The metal pole usually goes through the middle of the boat, and has several layers of plastic between the base, and the water.

And wires going throughout the vessel, often to larger conductive things, like engines, and steering.

The optimal solution. A 30mm copper rod higher than the mast, and insulated with ceramic standoffs run by a 00 gauge copper cable to a metal plate with a minimum surface area of 3 sq meters immersed in the water, should provide adequate protection as long as all electronics are powered down, and electrically disconnected, (military electronics are always in sealed metal boxes attached to ground with metal cannon plugs for wiring to shielded cables).


Towing a large metal sheet, or ribbon is often impractical during rough conditions, and most of us don't have copper plated hulls so that leaves a less effective compromise.

Minimum would be ground the mast to the keel, (If metal), or a below water conductor, (rudder, prop shaft, etc...).

Portable backup electronics, placed in a metal container, (metal pot with metal lid, or wrapped in aluminum foil).

And plan on buying new VHF, and wind instruments when you get a strike.

I just got to buy a new wind instrument after a nearby strike, so I have experience.

And just know, the less effort you make in providing a direct path to ground, the more damage you will get, (depending on the size of the strike, which can go from thousands to billions of volts, and dozens to hundreds of amps).
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Old 16-11-2020, 10:14   #73
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Re: Lightning Protection for Electronics

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Originally Posted by Singularity View Post
If I had money to throw at a lightning EE I would first contract someone who works lightning for Airbus/Boeing/big-time aerospace and would have a marine EE look at the plan afterwards.

The airplane guys actually deal with routine hits (with more on the line) while the marine guys have a lot of snake oil in their midst and/or their systems are in total less tested with who knows what outcomes.



That would be the GREAT Dr. Murphy, wouldn't it?
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Old 16-11-2020, 10:20   #74
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Re: Lightning Protection for Electronics

Quote:
Originally Posted by Frankly View Post
That is pure uniformed BS.

Lightning protection systems safely conduct strikes from their targets every day all over this planet.


Frankly
Absolutely true for many structures. But does it really apply to the recreational sailboat? We once had a large freighter ask for a position because the vessel had been struck by lightning and all of their electronics were out. All they had functioning was a hand held VHF. (They had a radio operator, who was useless except at that point.). I had a friend who was also a ham and ships radio operator. He aways carried his own modified ham rig, with a back up antenna, in a EMF resistant container on board the large ships he sailed on.

I did keep a hand held GPS and a hand held VHF radio wrapped in aluminum foil on an ammo box, which was sealed with metal duct tape aloud the lid. Never got to test it.

We had a large ketch with wooden masts, but we put chains from the chain plates and had a bob stay the lower part of the fitting was below the static water line. We also disconnected all electronics: antennas, positive, negative, grounds. We were in a lightning storm where almost all of the other boats in the harbor were struck and damaged. Over 100 strikes in an hour (In Yugoslavia). We had St. Elmo's fire in the rigging--but only damage was one diode for the mast head wind vane.

On a Cal 46 I put one of the dissipators on the masthead bolted with two SS bolts, the heel of the mast was on an aluminum structure spread over several bulkheads. I had 3/4" copper tubing from the mast just above its step to a 2 sq foot copper plate on the bottom of the boat. All shrouds and stays were tied in with #4 wire to the plate. We still removed all electronics from any conductor.

I sold the boat, and the new owner kept her at my dock in Pensacola, FL. I was out of town, and got a message that a power boat about 50 feet away had a direct strike on its antenna, and had significant damage. But the Cal 46 battery charger was running full 30 amps all of the time. I asked if the alternator was warm--the new owner didn't think so. When I got back in about a week, the alternator was warm, the isolating diodes had been blow. The battery charger was putting full power into the ground system. the prop was eaten, the shaft was eaten, the rudder shaft was eater as well as thru hulls. No damage to any electrical or electronic items. The assumption was a lobe came thru the water to the boat.

The boat was about 40 yards from my ham tower which had a "lightning rod" on it over 65' from ground, which went directly into moist sound under the tower--no damage. Why did the lightning hit the power boat antenna, about 20' high and not the 57' mast or 65' steel ham tower all of which were with in a circle of less than 100 yards and were well grounded? No direct strike, but a side lobe in the water caused extensive damage to metal via the battery charger.

I don't know if the new owner changed the lighting ground system I had installed. But the vessel's mast was hit twice in the next several years, with damage to the mast and inside the vessel--entire 110 V and 12 system was damaged, including water maker, refrigeration motors etc. All electronics were fried.

Would Ewen Thomson's most "modern system" prevented any of these strikes? I don't know. I know that the owner had contacted Dr. Thomson and asked for advice.

My advice is to follow Dr. Thomson's advice and system, but still have a way to easily disconnect the key electronics (including auto pilot) from all of the wiring.

Keep a backup GPS and VHF radio, each wrapped in foil, in a sealed metal can.
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Old 16-11-2020, 10:35   #75
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Re: Lightning Protection for Electronics

Quote:
Originally Posted by Singularity View Post
If I had money to throw at a lightning EE I would first contract someone who works lightning for Airbus/Boeing/big-time aerospace and would have a marine EE look at the plan afterwards.

The airplane guys actually deal with routine hits (with more on the line) while the marine guys have a lot of snake oil in their midst and/or their systems are in total less tested with who knows what outcomes.
Aircraft and marine lightening mitigation techniques are significantly different, You are right, AC are routinely struck by lightening with no ill effects, they are a faraday cage. Yachts need a good ground path, and I don't believe any system can prevent a strike. Agreed on the snake oil, no shortage of that.

More here https://www.proboat.com/2016/04/3530/
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