TVS Diodes for Lightning Surge Supression?

[Nicholson58]

Originally Posted by Andina Marie

Agree with David, lightning is so unpredictable the chance that your protection will help is minimal for a direct strike.

For induced voltages from an indirect strike, suppressors close to the item to be protected may help a little.

I remember years ago, a company was selling a lightning protector, it looked like an antenna with metal fur sticking out of the end. They GUARANTEED it would protect your boat and electronics by attracting the "pre-lightning" discharge or something like that and defusing the strike. It was a clever marketing scheme. For $199 (or whatever it was) they were selling you insurance on the instruments and it didn't really matter if you decorated your boat with the fuzzy antenna or not. Save your protection device $$$ and put it in a disaster bank account to buy new equipment.

I have one of those fuzzy things. It was undamaged in the massive hit we had last summer.

[colemj]

Originally Posted by Nicholson58

If one of these is required on each end of the antenna does that mean top of the mast too? One could be easily placed at the foot of the mast in the cabin floor.

What is particularly interesting is that our Simrad NSE8 with its broadband radar & depth scanner were all wired with air gap rocker switches so that they could be individually controlled. NO damage.

Yes, the one at the top of the mast is actually easier to install because one end goes directly on the antenna connector and the body is grounded straight to the mast (which is then bonded for lightning).

At the boat end, the coax must be split and a ground wire bonded properly. This latter is often difficult unless the mast is keel stepped and the suppressor can be connected to it similarly as at the top.

I wasn't questioning the air gap ability at the far end of branch circuits that would receive only a minimal amount of a surge. Rather, only their placement at the major entrance point of the VHF coax. To me, it would be better to short the conductor to the shield and connect both to the lightning bond. Instead of switches, it seems easier to have a pigtail already connected to the lightning bond, and simply disconnect the coax and plug into the pigtail.

Mark

[colemj]

Originally Posted by Nicholson58

I have one of those fuzzy things. It was undamaged in the massive hit we had last summer.

Since the fine print of the warranty only guarantees your money back for damage to the fuzzy thing itself - not any other equipment damage - you don't even get that satisfaction!

Mark

[EwenT]

Originally Posted by colemj

Wait, you have to answer my question first.

OK, I'll go first. Our mast grounding system is a commercial system called a "Strike Shield" (no longer in business). It consists of a mounting plate bolted to the mast above deck with a thick 4/0 cable connected to that plate and dropped overboard through the trampoline (we are a catamaran). The water end of this cable consists of a machined copper electrode with 15-18 feet of linear edge surfaces machined into it (it is ~12" long with 18 machined edges in it).

When we were struck, we noticed that the thick heat shrink plastic used to cover the connection of the wire to the mast connector was split opened and the electrode was missing the few barnacles and all the sponge/weed that often grows on the machined edges (we keep this in the water all the time). I usually have to pull this up and scrap it hard every so often, so finding it pretty clean was a surprise.

I don't have any photos, but could take one of the split heat shrink plastic since I haven't figured out how to correct that yet. It isn't very interesting, though.

Mark

So apparently the connection generated a lot of heat and something, probably electrolysis, cleaned the growth off the electrode, which is solid evidence that current flowed along this path. Did you notice any black spots or craters that could have been the result of sparks?

As to your question, the main problem with Domino's technique is that the long pigtails inherently increase the effective area of the circuit being protected, thereby increasing the induced voltage.

[hellosailor]

Mark-
"Maybe a better way would be to use a switch to short the coax to the conductor?"
Yes, in fact forgotten standard radio operator practice was literally "Pulling the plugs" when signing off the air. And that also meant physically pulling the antenna cable out of a "normal" plug and plugging it into an external ground connection (or one at the entry point) so that any lightning strikes would go directly to ground, at the point where the cable entered the building.


It would work equally well on boats. The problem is, you have to remember to physically get up and disconnect the rig, and then again remember to physically reconnect it when you come back aboard, or when the storm has passed. Or you need it for a mayday during the storm, oopsie.


I suppose that if you wanted to be fancy, it would be child's play to connect the antenna cable to a relay and transfer switch, so that powering the radio ON connected the antenna cable, and shutting it OFF, also re-connected it back to ground.


The cabin boy and electrician might call union actions on that, though. Never mess with the union.(G)

[colemj]

Originally Posted by EwenT

So apparently the connection generated a lot of heat and something, probably electrolysis, cleaned the growth off the electrode, which is solid evidence that current flowed along this path. Did you notice any black spots or craters that could have been the result of sparks?

As to your question, the main problem with Domino's technique is that the long pigtails inherently increase the effective area of the circuit being protected, thereby increasing the induced voltage.

If you meant black spots or craters in the hull, then no - the hull was closely surveyed for damage and none was found.

If you meant along the grounding system, then I don't think so, but the entire wire is covered in heavy black insulation and the electrode is fully submerged in water.

So you suggest that the TVS diodes be connected directly across the power terminals themselves? This is very difficult to do on the instrument end of power unless a terminal strip is used just before the instrument. It is easier to do on the distribution end of a circuit, but I think they are less effective there?

Mark

[EwenT]

Originally Posted by colemj

If you meant black spots or craters in the hull, then no - the hull was closely surveyed for damage and none was found.

If you meant along the grounding system, then I don't think so, but the entire wire is covered in heavy black insulation and the electrode is fully submerged in water.

So you suggest that the TVS diodes be connected directly across the power terminals themselves? This is very difficult to do on the instrument end of power unless a terminal strip is used just before the instrument. It is easier to do on the distribution end of a circuit, but I think they are less effective there?

Mark

I meant the actual electrode. Evidence of sparks is common in strikes in fresh water as discussed in a letter I wrote for Professional Boatbuilder in 2004. However, in salt water I have seen much less evidence. Since salt water is a much better conductor than fresh the voltages for the same current are much smaller, and may not reach the threshold for spark formation. So whether or not sparks form underwater in salt water strikes is indicative of the grounding mechanism. Note that there is a lot of confusion about some of the most basic terms used in discussing lightning physics. For example, NFPA 780 only uses "ground" as a verb, and "voltage" usually implies "voltage difference with respect to a reference". However, when I use the term "voltage" I am thinking of voltage gradients, that is, electric fields. If you are comfortable with all of these terms, my treatment of some of these concepts might be informative.

Yes, if the intention is to protect a particular circuit then the TVS should be placed across its power terminals, which I agree is difficult when the electronics comes with its own customized wiring harness.

[colemj]

There are definitely no craters in the electrode - not even small ones. It has been too long to determine if there were black spots - there are not any now.

I am familiar with all your work and appreciate what you have accomplished and shared. It has influenced me in how I approach lightning mitigation, although I cannot go as far as installing a full-blown system as you recommend - money, time and space/access prevent that. Instead, I am relying on applying your research to bond the boat and protect branch circuits as much as reasonable, and then keep my insurance up to date.

Mark

[transmitterdan]

Mark,

If you want to "roll your own" TVS circuit for a few devices like VHF, sailing instruments, MFD, etc. you can consider these parts:

2 each - Bussman FWC (10 A semiconductor fuse) http://www.mouser.com/ds/2/87/BUS_El...32A-349082.pdf

2 each - Littlefuse 3KP14A TVS diodes - http://www.littelfuse.com/~/media/el...asheet.pdf.pdf

Put a fuse in each of the + and - leads with the TVS diode across the +12V at both ends of the fuses. A circuit breaker cannot interrupt the current from a strike but these semiconductor fuses often can. They are filled with "sand" that melts and forms a glass insulator which tends to stop the current fairly quickly and hopefully before the TVS diodes explode. The 10A rating is somewhat arbitrary and you can size them up or down as appropriate.

This isn't a "guaranteed to work" solution but it can prevent damage in a lot of cases. The closer you can put the lashup to the "protected" device the better but it does not have to be super close to be effective. Just be sure the wires from the device to the TVS circuit are kept well away (say a few inches) from all metal and other wires. A small diameter piece of Polyethylene or Impolene tubing can be a good way to isolate the wires. The idea is to make it hard for the wires to arc to ground or something else before they reach the fuses.

The fuses are frightfully expensive ($25 each in small quantities). The diodes are <$2 in small quantities.

The fuse is 1.5" long so takes an unusual clip type holder but they can be had. The whole thing will take up a space of about 2"L X 1"W by 1"H.

Expect to replace at least one fuse and the diode when a direct strike happens. Most likely both fuses will open.

[EwenT]

Originally Posted by colemj

There are definitely no craters in the electrode - not even small ones. It has been too long to determine if there were black spots - there are not any now.

I am familiar with all your work and appreciate what you have accomplished and shared. It has influenced me in how I approach lightning mitigation, although I cannot go as far as installing a full-blown system as you recommend - money, time and space/access prevent that. Instead, I am relying on applying your research to bond the boat and protect branch circuits as much as reasonable, and then keep my insurance up to date.

Mark

Thanks for the information. I realize that many sailors are in a similar position in wanting to do something to mitigate the effects of lightning but have limited budgets and are restricted in what is feasible. So first-hand observations such as yours are invaluable in helping establish some crucial concepts that are still confusing to me. The mechanism of current flow from a submerged electrode in salt water is key to the development of the optimal grounding device. The StrikeShield electrode seems to have a good track record for reducing damage but, in your case, you observe After our strike, we could trace the path completely through the ground side - enter the boat through the VHF coax shield, jump from the VHF into the boat ground (most likely through the case), blow the fuses on the negative wires while leaving the positive wire fuses untouched, enter electrics through the case ground and exit through the engine ground taking out the alternator's internal regulator. which implies that current was also conducted from the VHF shield through the engine.

If you observe any other interesting features on your electrode surface, however subtle, I would like to hear about them. If I was involved in a forensic analysis and had your electrode on hand I would examine it with a microscope, but do not wish to influence your observations and so will not say what I would be looking for. Also, any features on your saildrive, prop shaft or propeller are relevant to the current flow through the engine.

[GordMay]

Daiwa Antenna Switches:
In the common position the common input line is disconnected from all antennas and all antennas are connected to ground.
➥ http://www.universal-radio.com/catftp/K048_048.pdf

FWIW: Along with Drs. Martin Uman & Vladimir Rakov, Ewen Thompson’s research has provided much of our knowledge of lightning (& boats).
Dr. Ewen Thomson (president of Marine Lightning Protection Inc.)
➥ http://www.marinelightning.com/profile.htm
➥ http://www.marinelightning.com/index.html

[rgesner]

Ewen,

If I may, a question or two about the differences between:

1. Mark's system which dangled a sophisticated custom machined electrode in the water.

2. The system you were developing when the Catamaran page on your site said you were "in the process of developing a bridge deck electrode. This is connected via a flexible conductor so that it can be lowered to just above the waterline, for maximum grounding effectiveness, or all the way up to the bridge deck, for clearance while cruising." (actually, it still says this)

3. Your new bridge deck electrode for catamarans, which is installed some distance above the water?

Although Mark's electrode is a thing of beauty, do you think it is any more effective than any other electrode of similar surface area dangled in the water? Perhaps even just a 4-0 cable with the end section stripped of insulation (tinned, of course)?

What do you believe is the comparative effectiveness of your new bridge deck electrode compared to the above?

Why, for your systems, are your electrodes just above the waterline, or even on the underside of the bridgedeck which could be 2-3 feet above water?

Lacking virtually impossible actual comparative tests, I'm just looking for an opinion based on your considerable knowledge.

Thanks - Rusty

[Andina Marie]

One company sells a grounding plate made from sintered copper. The theory is that the porous nature increases surface area and makes a lower resistance connection to the water. The theory sounds good but it totally "ungrounded".

The resistance of the salt water in the cavities is so high in comparison to the copper, it is only the outer entrance of the cavities providing the ground so a flat plate would actually provide more effective contact. Even with 100% of the plate connected to the water with zero resistance, the resistance to ground is still no less that the cross sectional resistance of the water in contact with the plate.

What is worse, during a lightning strike all those water filled cavities could generate steam and create an explosion.

[hellosailor]

"One company sells a grounding plate made from sintered copper."
That sounds like a knock-off or confusion with the DynaPlate. Which I believe is sintered bronze, not copper. And expressly sold as a radio ground, not a lightning ground, for exactly that reason. A lightning flash could cause the "trapped" water to superheat and explode. But AFAIK they do make clear the purpose and limits of their plate.

[EwenT]

Originally Posted by rgesner

Ewen,

If I may, a question or two about the differences between:

1. Mark's system which dangled a sophisticated custom machined electrode in the water.

2. The system you were developing when the Catamaran page on your site said you were "in the process of developing a bridge deck electrode. This is connected via a flexible conductor so that it can be lowered to just above the waterline, for maximum grounding effectiveness, or all the way up to the bridge deck, for clearance while cruising." (actually, it still says this)

3. Your new bridge deck electrode for catamarans, which is installed some distance above the water?

Although Mark's electrode is a thing of beauty, do you think it is any more effective than any other electrode of similar surface area dangled in the water? Perhaps even just a 4-0 cable with the end section stripped of insulation (tinned, of course)?

What do you believe is the comparative effectiveness of your new bridge deck electrode compared to the above?

Why, for your systems, are your electrodes just above the waterline, or even on the underside of the bridgedeck which could be 2-3 feet above water?

Lacking virtually impossible actual comparative tests, I'm just looking for an opinion based on your considerable knowledge.

Thanks - Rusty

Rusty,
Your questions are right on the mark. This exchange has been very fruitful in that Mark's objective observations have established, for me, some fundamental concepts and a clear direction as to the next steps. Here are some observations and opinions.

1. Mark distinguished between a "surge component", that exited through the engine, and the "main strike", that overheated the mast/cable connection and cleaned off the electrode fouling. To me this indicates that only lower frequency components of the lightning current were conducted through the immersed electrode. This is consistent with the well-known principle that high frequency electromagnetic waves are highly attenuated in sea water. In other words, a submerged grounding electrode is not effective at grounding the higher frequency components, where the verb "ground" means the transfer of current into or towards the ground medium, that is, the water. So we can expect the lightning system to reach a high transient voltage with respect to the water.

2. A key point here is where the lightning current actually ends up. The concepts are more complicated than most marine electricians have to deal with since the return current flow is a displacement current between the surface of the water and the thunderstorm. Here is a brief explanation written for the layman, with an illustrative animation. That is, the charge neutralized by the lightning current resides on the surface of the water. A long bridge deck electrode whose tip is just above the water surface seems like the optimum geometry to maximize the chance of a spark forming to the water surface, to establish the surface arcing, while minimizing the inductance of the down conductor path. While the concept is sound, the practical problems of fabricating an electrode with a flexible coupling that will withstand the marine environment, not flop around, and be reasonably priced have proved daunting. However, development is still under way.

Another idea was patented by Wally Hall who floated the electrode with its own bouyancy. My company has now purchased Wally's patent and development is underway on a floating electrode, which has its own set of issues.

3. A rigid electrode is straightforward to fabricate and install. However, if it is too long there is the risk that it could hit green water at speed and severely stress the electrode fitting and bridge deck. And the higher it is above the water surface the lower the chance of it initiating a spark (before something else does). So the present compromise in the minimal Tier 1 grounding system is to install two additional electrodes much closer to the waterline on the inner side of each hull.

Now, concerning the new direction I see this taking us:

A. Grounding devices While I have had very few issues with Siedarc electrodes, my line of immersed grounding strips has been plagued with corrosion problems. Other concerns are the need to drill holes below the waterline, drag, and several pounds of additional weight. My latest designs instead incorporate existing metallic fittings to act as immersed electrodes and the plan is to phase out the immersed strips.

The benefits of a bridge deck electrode whose tip is close to the water surface are clearer than ever. Expect to see the next versions of both flexible and floating electrodes out soon. Unfortunately I do not see an easy way to do this, otherwise I would have developed an inexpensive product years ago and every sailor would now own one!

B. NFPA 780 Standard The NFPA 780 Technical Committee is meeting this July and I plan to raise the issue of grounding to water once more with specific reference to the information in this forum. This topic is relevant not only to boats but also to docks and piers.

C. I am going on vacation Actually this was planned way before my immersion in this thread. So if you reply to this and do not get a response it is probably because I am busy riding a bike in the Pisgah National Forest.