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Old 04-07-2021, 10:40   #1
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Near misses of lighting - use ferrite beads to reduce induced voltage spike?

Hi folks,

I would be interested in hearing back opinions on some thoughts I recently had:

After some near misses by lightning strikes that made part of our electronics reboot, I thought, ok, near misses induce voltage spikes and the electronics does not like that.

So, why not liberally add ferrite beads at strategic places in plus and ground lines. (Data lines would also pick up surges, but beads would probably change the shape of the data signals and may create more problems there...)

Any thoughts on this idea? Crazy?

I have used up my entire supply of beads now to test the idea, but then again, I actually prefer if I cannot test it for lack of opportunities...

Cheers

Mathias
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Old 04-07-2021, 12:04   #2
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Re: Near misses of lighting - use ferrite beads to reduce induced voltage spike?

Extremely unlikely to help, but certainly will not hurt.

Ferrites are good at supressing high frequency low power radiation. Better at keeping IN the wire than keeping it OUT.

The problem with lightning is you have a current that goes from 0 to 50,000 amps in a few milliseconds, and then repeats three times. Very rapidly changing electric currents generate very powerful, and rapidly changing magnetic fields.

Powerful, rapidly changing magnetic fields, in turn, generate strong electrical currents in every nearby conductor. In the case of electronic equipment, it is actually those induced currents that cause much of the damage, and it doesn't matter if they are turned on, or even plugged in. Every solder trace on every circuit board puts out a power surge, and if that exceeds the tolerance of the attached circuitry--poof!

There are good reasons to have a proper lightning ground on a boat, but it is not going to save your electronics.
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Old 04-07-2021, 12:22   #3
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Re: Near misses of lighting - use ferrite beads to reduce induced voltage spike?

Hmm, yes, I can see your points.

Voltage will be induced inside the electronic devices, directly on the board. I can see that. But then again, induced voltage on a line is related to change of magnetic flux through the area that is enclosed by that line. The area on boards spanned by wires there is much smaller than outside. So, a wire that forms part of a loop in the vessel can pick up much more voltage than a bent wire on the board can. But certainly, that wire on the board may be part of a very sensitive circuit that does not tolerate a lot.

Or am I missing something vital here?

Cheers

Mathias
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Old 04-07-2021, 12:56   #4
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Re: Near misses of lighting - use ferrite beads to reduce induced voltage spike?

Ferrites will do nothing to prevent lightening damage. The energy is far far to great for a ferrite to have any effect
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Old 04-07-2021, 13:04   #5
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Re: Near misses of lighting - use ferrite beads to reduce induced voltage spike?

Certainly the length of the antenna and enclosed area are a big part of the induced voltage (along with the distance and intensity of the strike).

Common mode chokes typically would have little effect on the normal mode voltages (signal or DC supply). The idea here is to provide some impedance to a circuit as both + and - sides of the circuit voltage rises in respect to a common reference (usually ground). Most of the information on "lighting robustness" suggests that the induced common voltages are the most destructive. IE an induced surge elevates the level of both conductors to say 1,000 volts and a component referenced to ground goes pssst.

Several years back I added a rather extensive array surge protection devices to my already robust mast ground. Most were shunt type surge suppressors but a few common mode chokes where convenient. So far so good and last night it was put to a pretty good test (one of them "only in Florida lightning storms"). Everything was still working this morning.

There are some pictures (protection components not lightning storm) in my album if any one is really interested. By fabricating most of my own units the cost was rather minimal. A little work but me and my electronics sleep better.


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Old 04-07-2021, 13:14   #6
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Re: Near misses of lighting - use ferrite beads to reduce induced voltage spike?

Gas discharge tubes is what you need and those are in lightning arrestors like this one: https://www.amazon.com/Lightning-Arr...s%2C194&sr=8-4

Also available for Ethernet etc.
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Old 05-07-2021, 09:29   #7
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Re: Near misses of lighting - use ferrite beads to reduce induced voltage spike?

The problem with lightning is you have a current that goes from 0 to 50,000 amps in a few milliseconds, and then repeats three times. Very rapidly changing electric currents generate very powerful, and rapidly changing magnetic fields.QUOTE]

I think what the OP is talking about here is “near misses”. Of course defining near misses is somewhat subjective.

I’m not sure what ferrite toroids will do for him but it might help if the near miss is not the 50000 amps of a direct hit. In the case of a direct hit, he is probably toast regardless what he does (except being amazed at what a direct hit is capable of)
:<{

I saw the results of a direct hit on a house that burned the foil based wall paper inside the house. It was suspected that the energy came into the house via the sprinkler system. Fortunately my friends weren’t at home when the strike occurred. It must have been a spectacular display for a second or two.
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Old 05-07-2021, 10:29   #8
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Re: Near misses of lighting - use ferrite beads to reduce induced voltage spike?

Exactly, I know things will be toast when they get a direct hit by the lightning strike.

But near misses are much more common, and if the lightning is far enough away, there must be a distance where the induced voltage has become small enough that ferrite beads may be effective. If placed correctly. The question then is whether they can offer protection for a reasonable range of distances of the lighting flash, or not.
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Old 05-07-2021, 13:49   #9
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Re: Near misses of lighting - use ferrite beads to reduce induced voltage spike?

Hi Frankly,
I'd be most interested in viewing your album of protection components. Where can I access ?
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Old 05-07-2021, 15:02   #10
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Re: Near misses of lighting - use ferrite beads to reduce induced voltage spike?

Quote:
Originally Posted by BobFord View Post
Hi Frankly,
I'd be most interested in viewing your album of protection components. Where can I access ?
I think if you just click on my name it will take you to my albums. No guarantees with any of this, just trying to move the odds a little. In over 55 years of boat ownership in Florida replaced a significant amount of equipment. No evidence of a direct strike ever.

In the hiercharchy of LP components varistors most common, surge protection diodes (DC only), and gas discharge tubes. GDT are most typically found when protecting RF components (HF and VHF radio antennas) when capacitance can be an issue. Used them all.


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Old 06-07-2021, 15:12   #11
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Re: Near misses of lighting - use ferrite beads to reduce induced voltage spike?

i took a direct hit by lightning - masthead to god knows where it exited.
have posted here several times about my experience. did not have a lot of built in electronics - radio, depth sounder, navtex. all three were not working after the strike. i checked all the fuses on their positive wire. none were blown. then i noticed that the furuno navtex also had a fuse on its negative wire. replaced that and up it came.

my take? the strike came down the negative side and only the navtex was protected.

my advice? fuse the negative wire on anything you want to protect.
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Old 06-07-2021, 15:15   #12
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Re: Near misses of lighting - use ferrite beads to reduce induced voltage spike?

Quote:
Originally Posted by onestepcsy37 View Post
i took a direct hit by lightning - masthead to god knows where it exited.
have posted here several times about my experience. did not have a lot of built in electronics - radio, depth sounder, navtex. all three were not working after the strike. i checked all the fuses on their positive wire. none were blown. then i noticed that the furuno navtex also had a fuse on its negative wire. replaced that and up it came.

my take? the strike came down the negative side and only the navtex was protected.

my advice? fuse the negative wire on anything you want to protect.
My only question is... is your boat positive of negative ground?
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Old 06-07-2021, 15:25   #13
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Re: Near misses of lighting - use ferrite beads to reduce induced voltage spike?

yes it has a negative ground. i am not a lightning scientist but i know that the strike is seeking a ground and it grounded right through my masthead to god knows wherer.

by the way, the boat is not grounded per se - that is it has no external ground plate that everything is coinnected to, the thruhulls are not connected to each other, none of those things associated with doing a thorough ground system exist in the boat.
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Old 06-07-2021, 15:27   #14
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Re: Near misses of lighting - use ferrite beads to reduce induced voltage spike?

Great, thanks I was just curious. It's interesting that the fuse was enough to presumably help.

Ben
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Old 06-07-2021, 15:29   #15
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Re: Near misses of lighting - use ferrite beads to reduce induced voltage spike?

if memory serves the fuse was just 1 amp.
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