Isolated and hardened DC power for electronics

[s/v Jedi]

Originally Posted by fxykty

We have a wired wind instrument at the masthead with a cable all the way down the mast to behind the navigation desk where it connects to our Seatalkng network. Almost all of our instruments and radios are connected to it in some way, whether through direct cable connections or via a multiplexer. Sigh.

We also have two antennas at the top of the mast, each with LMR400 cables also running all the way down to splitter and router respectively.

Aside from the mast itself, those three cables are the only way for lightning to get to ground with our boat, as we are a cat with a deck-stepped mast and all synthetic rigging. Other than drinking gin and tonics I’m not sure what else we could do to mitigate a direct hit.

I know it’s not easy for a catamaran, but you have no bonding of the mast at all? I know of some cats that devised a system where they can drop a bonding wire down from the bridge deck into the water to bond the mast with the sea.

We have two keel-stepped masts and each has a bonding wire straight down to a bonding plate in pockets under the hull so they sit flush. A sharp bend in the wire would invite the surge to jump over to something else.

This bonding has prevented major damage during the many lightning strikes we had, but of course still much electronics was lost.

I am about to decide to not put any radios on this isolated supply. Besides the difficulty of keeping DC negative isolated with all the coax and antenna mounting, there is still that big risk of lightning hitting the antenna. We have had that happen multiple times.

The wind instrument…. makes me think about the wireless version again. I still don’t want that though, but we had lightning strike this as well so we need to find a way to disconnect it. I tried alternative mounting positions but none were good enough to get the autopilot to reliably steer to a wind angle. I think physically disconnecting it is the way.

[team karst]

Several reasons I dont have synthetic static rigging. Yes, i am paranoid. Lightning mitigation becomes even more difficult, and i dont want such a fragile support system that a fool with a small knife can bring the entire rig down in 10 seconds. I know i stand in the minority with this…

[s/v Jedi]

Originally Posted by team karst

Several reasons I dont have synthetic static rigging. Yes, i am paranoid. Lightning mitigation becomes even more difficult, and i dont want such a fragile support system that a fool with a small knife can bring the entire rig down in 10 seconds. I know i stand in the minority with this…

Good point, but I don’t think lightning will have the patience to travel through the high resistance of stainless steel when there’s a juicy aluminium or carbon fiber mast as a highway straight down towards ground potential.

I remember as a kid my father attached chains to the stainless rigging wire and hang that overboard…. with a steel hull just because everyone in the marina did that

[team karst]

all true; SS is not the prime choice for voltage drop. At some 42x the specific R as pure copper. However, it is 12mm dia, and does have a very high melting point. I'm betting all that the still less than 1Ohm top to bottom will help a lot.

[fxykty]

Originally Posted by s/v Jedi

I know it’s not easy for a catamaran, but you have no bonding of the mast at all? I know of some cats that devised a system where they can drop a bonding wire down from the bridge deck into the water to bond the mast with the sea.



We have two keel-stepped masts and each has a bonding wire straight down to a bonding plate in pockets under the hull so they sit flush. A sharp bend in the wire would invite the surge to jump over to something else.



This bonding has prevented major damage during the many lightning strikes we had, but of course still much electronics was lost.



I am about to decide to not put any radios on this isolated supply. Besides the difficulty of keeping DC negative isolated with all the coax and antenna mounting, there is still that big risk of lightning hitting the antenna. We have had that happen multiple times.



The wind instrument…. makes me think about the wireless version again. I still don’t want that though, but we had lightning strike this as well so we need to find a way to disconnect it. I tried alternative mounting positions but none were good enough to get the autopilot to reliably steer to a wind angle. I think physically disconnecting it is the way.

Our mast isn’t grounded - it sits on a thick aluminium plate on our main beam and no ground wire exists (unless laminated into the deck, not likely).

We’re thinking of bolting a spare length of 70mm^2 wire to the base of the mast and drop that into the water during a lightning storm. I assume creating a ground system doesn’t make our mast more attractive to a random bolt?

[fxykty]

Originally Posted by team karst

Several reasons I dont have synthetic static rigging. Yes, i am paranoid. Lightning mitigation becomes even more difficult, and i dont want such a fragile support system that a fool with a small knife can bring the entire rig down in 10 seconds. I know i stand in the minority with this…

Someone with a knife would have to be very deliberate to cut through two layers of braided covers plus the stay itself. If that’s an intent to deliberately cause damage, they could as easily use bolt cutters on your rig, the same one they’re already carrying to steal dinghies.

[noelex 77]

Originally Posted by goboatingnow

In my lightening strike it made no difference whether devices were powered up or not The strike propagated around the nmea2000 bus and took out all devices connected to it.

Every strike is different. It is possible to save the majority of electronics only in a mild strike.

We had such a strike around a decade ago. Everything electrical that was on at the time of the strike or anything with a component outside (for example radar) no longer worked. However, everything that was turned off and mounted inside the boat was undamaged.

So there is some benefit disconnecting electronics, but it is not a guarantee that all equipment will survive.

[s/v Jedi]

Originally Posted by fxykty

Our mast isn’t grounded - it sits on a thick aluminium plate on our main beam and no ground wire exists (unless laminated into the deck, not likely).

We’re thinking of bolting a spare length of 70mm^2 wire to the base of the mast and drop that into the water during a lightning storm. I assume creating a ground system doesn’t make our mast more attractive to a random bolt?

That should work as long as the wire doesn’t make sharp turns. Make sure there’s good contact and don’t connect copper to the aluminum mast… aluminum wire would be perfect for this.

[goboatingnow]

Originally Posted by noelex 77

Every strike is different. It is possible to save the majority of electronics only in a mild strike.



We had such a strike around a decade ago. Everything electrical that was on at the time of the strike or anything with a component outside (for example radar) no longer worked. However, everything that was turned off and mounted inside the boat was undamaged.



So there is some benefit disconnecting electronics, but it is not a guarantee that all equipment will survive.

Tne point is “ hardening against “ strikes is a waste of time

[s/v Jedi]

You can’t do much if anything against a strike. But you can do a lot against a near strike.

Isolating a power supply to harden your system against all kinds of negative effects from outside is a proven method, nothing to argue against unless arguing is the goal.

[goboatingnow]

Originally Posted by s/v Jedi

You can’t do much if anything against a strike. But you can do a lot against a near strike.



Isolating a power supply to harden your system against all kinds of negative effects from outside is a proven method, nothing to argue against unless arguing is the goal.

Most people involved in hardening things tend not to use ordinary off the shelf commercial things

[team karst]

Originally Posted by goboatingnow

Most people involved in hardening things tend not to use ordinary off the shelf commercial things

I guess i am not ordinary, at least with piece parts

Thousands of examples of surge, RFI, EFT , ESD hardened electronics in el power industry

NASA uses wire strung high around launch vehicles, right? Pretty low tech. Not saying cheap tho …

[goboatingnow]

Originally Posted by team karst

I guess i am not ordinary, at least with piece parts

Thousands of examples of surge, RFI, EFT , ESD hardened electronics in el power industry

NASA uses wire strung high around launch vehicles, right? Pretty low tech. Not saying cheap tho …

Few of these get by a big battery

[team karst]

Most of our stuff is qualified to run on 125/250V dc feeds from very large battery banks. However, these are non-earthed schemes, meaning very large common mode spikes can exist. The battery does eliminate ( mostly) normal mode transients.

[goboatingnow]

The next way to harden your electronics is fit copious TVS based surge suppressors on the dc fed in to each device and fit specialised TVS solutions on the nmea 2000 lines of in use.
That’s thd best way to harden things