andyalford avatar image
andyalford asked

Isolated DC-DC Converter to offer Lightning Protection to Navigation Electronic

Some years ago, my yacht had a 'little' lightning strike, and the effect to my complicated electronics was extensive. I am an EE, so I have fixed most of the items myself, and made an interesting project out of it!

My observation was that the ground side of the power input circuit was the only damaged item on the sensitive electronic items (B&G displays, NMEA multiplexor, fridge controller, almost anything with a status LED, etc.) A change of the input diode or regulator fixed many things.

I don't want to start a debate about protecting a boat from lightning, as I think it is pretty much impossible. But I can confirm that I have a heavy copper connection from my keel-stepped mast to my lead keel.

Now that I am re-wiring to accommodate my lovely LFP batteries and new Victron system, I am considering adding an isolated DC-DC converter to a small 12V battery to drive all the electronics. My main objective would be to have a "floating earth" for that separate system.

I am hoping that the DC-DC converter would die 'when' I next get struck, and it would save all the other electronics.

Would this be a likely case? I don't expect any guaranties, but wondered if anyone could comment that this is a possible path to go. Given that I am redoing all the wiring it is not a big issue to isolate the "Electronics GND wire"

Thanks for your thoughts..

Orion DC-DC Converters not smartisolatorsdesign
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1 Answer
kai avatar image
kai answered ·

I went through (and still am I guess) a fair bit of analysis, looking at various approaches etc before kinda maybe committing to open ended solutions :D

I think it really depends on the hypothetical scenario you're facing and the strength of the threat.

A (significant) direct strike imo is more about managing the risk of fire, electrocution and loss of structure. The induced currents as a result of diverting a strike through the downconductor is highly likely (again imo) to bypass almost any electronic protection that you might have simply because of the surge magnitude and physical proximity.

Indirect strikes on the other hand, you may have a better chance because the magnitudes are lower.

The failure scenarios I'm thinking of are:

1) Surge at input of DC/DC is stopped at DC/DC

2) Surge at input of DC/DC blows through and is present at output with a reduced magnitude

3) Surge is coupled to output (through environment external to DC/DC)

The 3rd one is a doozy because of physical proximity and conflict with functional needs.

If you have a depth sounder, does the transducer look like a small earthing device wired to the 12v system? The potentials involved in a direct strike is not going to blink at the DC/DC's isolation rating.

More broadly, I think of lightning protection on a boat as needing layered defences, including physical separation, isolation, diversity, modularity, etc. An isolated DC/DC converter is one single layer - not a bad one but I wouldn't go so far as to say its sufficient on its own.

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andyalford avatar image andyalford commented ·

"The potentials involved in a direct strike is not going to blink at the DC/DC's isolation rating." made me laugh. You are completely right.

My 'last strike' must have been indirect, as we suffered no structural concerns. The only physical damage was to the VHF antennae, which landed on the deck!

Wifi is a good way to isolate things, in our modern 'black mirror' world. I had 2 Sony waterproof tablets and 2 Sony waterproof phones on the boat. They were all fine.

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kai avatar image kai ♦ andyalford commented ·

Yup, I'm planning on having spare and fully functional units on board for critical stuff in a metal case, and non-power wiring is all optical as far as possible).

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andyalford avatar image andyalford kai ♦ commented ·

Interesting. How do you do optical? Can you send any links? Thanks

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