TVS Diodes for Lightning Surge Supression?

[msponer]

Hi,
What do you guys think of using TVS Diodes for lightning surge suppression on 12v circuits?

I got the idea from MV DOMINO’s blog where he put 17 volt 15kpa TVS Diodes on every circuit. The photo below is from his blog. They cost about $7/each.

I know the diodes should be installed as close to the device as possible, but it’d be way easier (and cleaner) to add them across the load side of our 2-pole breakers. This is only about ~3’ of wire from all of our sensitive electronics, and ~15-20' to various motors and lamps. Or do you guys think a hypothetical surge coming in through one devices wires would induce a current in the other wires in the bundle thats headed to the breaker panel, and that’s why it’s important to put these diodes as close to each device as possible? I don’t know the science, at all, though it seems like the diode would clamp the power leads together and prevent the device from seeing anything over 17 volts regardless of where it is, and that the length of the run before the diode is mostly just impacting how long it sees the surge. Also, the failure mode for these diodes is 'permanent short circuit' -- which I feel I'd want right at the breaker instead of at the end of a wire run that's just transmitted a lightning strike. What do you guys think?

Why did the gentleman on MV DOMINO use unidirection diodes? It seems like bidirectional ones would be better, in case the surge is on the ground side of the circuit…? Bidirectional diodes are also in stock at the various electronics distributors, and unidirectional ones are not.

We plan to head to Panama later this year, where lightning strikes are common. I am replacing all of our breakers with 2-pole DIN rail mounted ones to help maintain the floating ground on our aluminum boat. I could add these diodes for little cost or time. I of course don't expect them to protect us completely, but I'm guessing they could help?

I would also copy MV DOMINO’s VHF surge arrestor strategy of adding a Polyphaser VHF50HN-MA to the VHF and AIS antennas. And the GPS and satphone antennas, if I can find the right part numbers.

Thanks,

Matt

[msponer]

Oh, duh -- only unidirectional diodes would work for DC.

[Andina Marie]

You can use bi directional protection diodes on DC, you are just using half of it.

And during a lightning strike the voltage across the device could be reversed momentarily so the bi directional diode "could" help.

HOWEVER, the amount of energy they can absorb is microscopic compared to the energy in a lightning strike, or even the induced energy from a near-by strike so the chance they will do any good is probably not worth their cost. The money would be spent much more effectively on insurance .

At the buss-bar or power switch level of the circuitry they would be totally useless. If you are going to stop a freight train you don't string a chain across a main line. At the device to be protected with all the branch line wiring between to add some "cushion" the train will have lost a lot of energy so the chain across will be more effective but still nearly useless.

[msponer]

Thank you.

Do you feel these pluggable DC surge protectors are any more or less helpful than TVS diodes?

They are ~$40/each instead of $5-7, so I'd have to feel more confident they would do something before getting one for ~36 DC circuits. But we could put them on the handful of nav light wires coming down from the mast, if that could help keep the surge away from the rest of the electronics.

That is, if they are likely to decrease the damage?

[David M]

Given lightning has enough voltage to arc for miles through a poor conductor (air), lightning certainly has the potential (no pun intended) to arc across two well conducting metal conductors a few millimeters apart on each side of a diode.

Diodes are also rated for up to a certain voltage. When that voltage is exceeded (more than 100 million volts for lightning) then all guarantees are off.

[msponer]

Originally Posted by David M

Diodes are also rated for up to a certain voltage. When that voltage is exceeded (more than 100 million volts for lightning) then all guarantees are off.

You no doubt know more about this than I do, but I believe the protection from the TVS diodes is that they short circuit the + and - leads if there's more than a 15 volt difference between them. So when the 1 kazillion volt lightening surge runs through the + or - wire, the diode clamps and sets the voltage difference between the wires to ~0-15 volts. So that's all the device see's, even though it's + and - are a kazillion voltes above everything else. And the failure mode is that the diode clamps permanently, and continues to short circuit the leads after the lightening passes: continuing to protect the device, but also tripping the breaker and making it inoperable.

Do you know different? I majored in physics, which sounds fancy until you know that I am one of those guys that only graduated from college because my professors liked me...

I feel that the telecome/cell tower folks wouldn't buy the DC suppressors if they were snake oil. I mean, at some point, someone smarter than me has to decide it's worthwhile to install them in their equipment. But then, they have a different environment from a boat sitting in the middle of an anchorage. Maybe they have more near-misses than a boat would, and that's where the DC surge suppressor works. And maybe the suppressors only work for near misses. Or in an environment where the main part of the strike is already routed to a big fat pipe in the ground. I don't know.

This whole thing is, like, way beyond what I know.

[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.

[rwidman]

The problem with any "home grown" lightning protection scheme is that you have no way of knowing if it will work until the time it's needed. Better would be to contact one or more companies that specialize in this field and see what solutions they have.

[autumnbreeze27]

Originally Posted by Andina Marie

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.

Our boat has one of those... is that insurance policy transferable? Do I just have to bring them the melted remains to get my electronics replaced if we get struck by lightning?

[trifan]

Diodes are good, as far as they go... as mentioned, they are better than nothing but against a lightning strike, fugettaboutit. A direct hit ain't pretty. A friend took a direct hit to a power pole outside his house and lost computer, modem, router, monitor, video surveillance system, refrigerator and an air conditioner. All (except the fridge) were connected to UPS power (battery backup, surge protection) and, oh yeah, it got the UPS unit, too. Lightning is not your friend.

I have designed/built hardened equip with gas-discharge type surge supression with fast s-bar clamping for voltage levels below the g-d threshold but even that level of protection is useless against Thor's hammer.

As a previous poster said, be sure you have insurance and make sure it is replacement cost insurance because if you take a direct hit you will need it.

[msponer]

Thanks for the thoughts. Do you think it would be better to get nice quick disconnects and completely unplug important electronics and antennas? Or is an off 2-pole breaker nearly the same?

It's not just money to replace the stuff -- it's the time waiting for it all to arrive in Panama and then reinstall it. So I am happy to do 'easy' preventative measures.

[seasick]

Met a boat in Panama two years back that took a direct hit. They had electronics that were still in the box (read, connected to nothing) that got fried. They had good insurance and ended up with all new electronics.

[AnchorageGuy]

It would seem from your responses that you have already made up your mind and are looking for approval rather than advice. You have already received good advice that this is an effort in futility. The only thing you will accomplish is to add many more connections that can come loose or corrode and that's without a confirmation as to whether these devices are going to generate voltage drops in the circuits. I agree with the others and IMO this is a complete waste of time and money as well as introducing a number of potential problem and failure areas in your electrical system. But if you need to do this for your own peace of mind, go for it and let us know if your one of those rare boats that actually gets a strike. Chuck

[msponer]

Originally Posted by AnchorageGuy

It would seem from your responses that you have already made up your mind and are looking for approval rather than advice. You have already received good advice that this is an effort in futility.
...

Really? Thank you for your input, I appreciate having a reality check on the conversation, but I feel you are being unnecessarily hostile. Why?

I am asking questions because I know nothing about lightning protection. Is anything better than doing nothing? Or is everything futile? If anything is possibly helpful, about how possibly helpful, and how much time and money is it to do?

I am not asking for advice on how to construct a dowsing rod. Lightning suppressors exist. Trifan said he's designed them, and then also said they sometimes don't work. But are they completely futile? Why would people pay him to add them to a device if they are worthless? I see lightning suppression modules for sale for cell towers. There's an IEEE standard for lightning protection. So someone must think you can do something. In some cases. Are those cases at all like what an anchored boat experiences? Or no -- in the case of boats -- does nothing work well enough to even bother trying?

I don't know.

[AnchorageGuy]

Sorry if you took that as hostile, it wasn't meant that way. Just a statement of how I see your responses and my opinion on your potential exercise. There are many, many discussions out there on lightning if you Google lightning protection for boats you will find enough reading for a long time. Our boats are not land based or radio towers so applications that apply to those situations will have little bearing on protection for your boat. There are many theories and a lot of hype from manufacturers that make claims they really can't back up. So it's hard to filter out the facts. But there will be underlining threads of information that will show up in most of these discussions. One fact that will quickly jump out is that a small piece of wire or diode will be useless in a direct or even a near strike. The best effort is to concentrate on preventing a strike, but even this is speculation at best. So a little research on the subject to gain some insight and knowledge will lead you down a path that can perhaps generate better results. Being in the marine service business for 40 years, I can tell you some stories of owners that have modified system to achieve perceived results and spend years professing to others how it prevented every type of catastrophe known to boaters, when in the end, it was just a matter that the boat or owner had never been presented with any kind of catastrophe. The true test only comes when the modifications are done and the lightning hits the masthead. Then and only then will you know for sure. Chuck