For those who depend upon electronics...

[CarlN]

Walt,

This is fascinating and well past my electronics knowledge. For the price of those diodes ($6 for 10) it would seem worth installing a bunch on sensitive electronics - even if it's just a "placebo" for the lightening worried skipper. Any reason not to? Both positive and negative leads?

I'm thinking here of Maine Sail's situation. Not a direct hit but close enough to do real damage.

Carl

 

[walt]

The part I referenced can definitely make electronic equipment more tolerant to a lightning strike but are going to be much more effective if they are part of the circuit design (ie, internal) and designed in based on testing to a spec.

However.. I think they probably would "help" (how much I don't know) if placed external. You can only place this particular part externally on the 12 volt DC power lines. The transorbs can be used to protect antenna inputs but this must be part of the design (internal) using a circuit known as a "bias T".

Still... if you wanted to place them on the DC voltage inputs, put the transorb as close as possible (ie, very-very-very close) to where the DC goes into the electronic equipment. The"cathode" goes to positive 12 volts and the "anode" goes to negative 12 volts (ie, ground). Since this part is basically a "zener diode", the single part will clamp both positive and negative transients. Just don't accidentally reverse the DC voltage going to the transorb, you will likely hear a "pop" and see a puff of smoke.

 

[Stu Jackson]

- even if it's just a "placebo" for the lightening worried skipper. Any reason not to? Both positive and negative leads? I'm thinking here of Maine Sail's situation. Not a direct hit but close enough to do real damage.

Carl, I'm having difficulty following the logic. $6-$10 each, two or three devices (VHF, GPS, radar) now you're up to $30 plus time & materials for nothing? (i.e., "placebo").

While we're very fortunate here in Northern California that we do not have the lightning storms most of the rest of the country suffers with, I fail to understand how this would be a cost effective "anything" to say nothing of a solution, especially given this discussion.

My understanding of Maine Sail's situation, and the diodes under discussion is: pretty much nothing would have protected the equipment.

Even BoatUS says this about lightning:

[FONT=Verdana, Arial, Helvetica, sans-serif]Lightning

Can you do anything to prevent your boat from being hit by lightning? Yes! No! It depends! So say the “experts.” The bottom line is there isn’t anything you can do if lightning takes a shine to your boat. There are many accounts in the claim files of boats equipped with lightning protectors that were damaged by lightning. Experts agree, however, that there are ways to mitigate the damage from lightning. A proper lightning bonding system will direct the strike to the water, hopefully before it can get into mischief aboard.

Most often, lightning strikes while the owner is away and the only signs of a strike are burned fuses and inoperable electronics.

I wish you all the best of luck this season with the weather you have been having.
[/FONT]

 

[Witzend]

I have to agree with Stu here, not much can be done to protect equipment, especially if the EMI is so strong that stuff is fried that is not even connected. For marginal strikes, strikes in the water with proximity to the vessel, I would think it would make sense to isolate any path from the water to the DC ground when systems are not in use.

 

[walt]

well.. I mostly agree also. But you also have to consider that you can have a huge range of emp, etc from a lightning strike. A direct or almost direct strike, kiss your electronics good by. A far away strike - maybe nothing to worry about as is. But in-between, little things like adding the transorbs on DC lines "could" decrease your odds of having damage. Are DC lines where you are most susceptible? Don't know, depends on the design. If the design has some big internal capacitors on the DC input, adding the diodes probably wouldn't add much protection. On the other hand, DC lines are generally not shielded and long runs and are going to be good for generating surge from EMP. Maybe something like simply using twisted pair wire for DC runs would also help? FYI, Im personally not going to add any diodes or go to twisted pair wires.. I sail in a fairly high lightning area so do worry about family safety and the boat sinking however.

One thing which is somewhat interesting in the current lightning threads is the idea of maybe having some key safety electronics in a protected enclosure (such as a GPS and hand held radio). The enclosure would need to shield for both electric and magnetic fields - so one enclosure might be aluminum (even aluminum foil) and this would be then put inside another enclosure that a magnet would stick to. Would this still be enough - no way to really tell.

 

[Bill Roosa]

Why aluminum foil and a iron box??

If the box is feromagnetic (magnets stick to it) then it also conducts electricity. No need to wrap the unit in aluminum foil too.
The corolary does not work as aluminum will not shield from magnetic force.

 

[Ross]

Re: Why aluminum foil and a iron box??

Probably a metal lunch box would be adequate.

 

[walt]

In a link posted earlier, the electric field shielding effectiveness was proportional to the basic conductivity/volume of the material and the thickness of the material. Aluminum is almost than 7 times more conductive than steel - which is good - but Aluminum foil is very thin - which is bad.

So maybe if you were real anal about this (is there an emoticon for being anal?), put the safety electronics in a steel lunch box - then put the whole thing inside an aluminum enclosure (like a pressure cooker).

Mainesail, maybe you can do another science experiment with different configs and get struck by lightning again.. Ok, maybe not.

 

[kenn]

Walt, thanks for the link to the MOSORB diode and for the mention of the big sparking machine thingy. Was any protection strategy able to survive the maximum output of that generator?

Thinking tangentally - Mainesail mentioned how even alot of unconnected equipment were damaged. For disconnected and stored 12 electronics, would it make sense to short the 12v power leads together, and short out any inputs (eg a shorted connector at the antenna in of a VHF radio)? Would this reduce EMI pulse damage, or would this simply provide another spot to induce current?

 

[Snotter]

In a link posted earlier, the electric field shielding effectiveness was proportional to the basic conductivity/volume of the material and the thickness of the material. Aluminum is almost than 7 times more conductive than steel - which is good - but Aluminum foil is very thin - which is bad.

So maybe if you were real anal about this (is there an emoticon for being anal?), put the safety electronics in a steel lunch box - then put the whole thing inside an aluminum enclosure (like a pressure cooker).

Mainesail, maybe you can do another science experiment with different configs and get struck by lightning again.. Ok, maybe not.

I am no lightning expert, but, it seems to me that the most destructive currents associated with a bolt stems from high-frequency electro magnetic fields. High frequency AC currents travel on the surface of conductors. At VHF frequencies and above, I would think foil would be thick enough. The wavelengths associated with low wavelengths are so large that it wouldn't couple well to circuits that fit inside a small ship much less a yacht. (Just thinking out loud here.)

 

[walt]

You can make "ports" (such as an antenna input) pass at the highest level the instrument will put out. For example, if you put two of the transorbs I linked to earlier in parallel and the coupling to the transorbs was robust enough (such as thick enough circuit traces or coupling discrete components which can handle the transient power), Im reasonably certain you can make something pass at the 6KV level. But this increases the cost of the device.

However, this is only testing the port for surge which would come in from some sort of wire connected to the port. It doesn't really test for internally generated transients (which probably is what damaged for example the GPS wrapped in aluminum foil). I think the only people who test stuff for actual EMP are the military contractors. With consumer stuff, at some level of EMP, it will just burn out.

Snotter, I think your correct. I don't have the exact numbers on the surge generator instrument but I believe it has a rise time in the under 10 usec range and a fall time in the few tens of millisecond range. The main energy of this is fairly low frequency. We also test for static discharge (ie, touching a door knob after walking over a carpet) and this instrument has something like a 10 nsec rise time - much higher frequency content than the lightning surge generator but also a huge amount lower overall energy.