Re: [electricboats] Grounding.

James,

There are several issues related to grounding:

1) Galvanic corrosion issues.

2) DC / AC safety (as it relates to whether to tie the AC and DC systems with a common ground).

3) Risk to swimmers in the water near your boat (stray electrical current getting into the water - though this is kinda' related to (2) above.

4) Lightening.

The Lightening issue is separate from the other three issues.

The general guidance for that is as below (and this may be miss-quoted or messed up, so please take my input with a grain of salt - don't trust what I'm saying, just consider it as a place to go research further...  I am NOT an expert on any of this, but trying to relate what I've heard over the years.)

Lightening will seek the Shortest and Best path from the hit point to ground.  In the sailing community, people have seen lightening hits strike the mast, run down, and blow out a thru-hull fitting because that was the only path to ground (water).  If there is no path, I have heard that the osmotic water in the fiberglass can be heated to the extent that significant hull damage occurs (including melting and/or blowing out the thru-hull, which could causing sinking...)

Many others have experienced lightening strikes or near misses that were not nearly as dramatic - nothing compromised the hull.  However, the strike did fry all the electronics on the boat.

I seriously doubt that fusing (or even double fusing) will help with that.  Won't hurt, but probably won't help.  You're dealing with a voltage surge that is off the charts.

If you're worried about lightening strikes, there are two common thoughts:

a)  Install a large metal plate (preferably copper) on the outside surface of the hull, and bond that plate to the mast, so that the mast is grounded.

b)  The rumored "poor man's approach" is to at least take a heavy set of jumper cables, clip one side to the side shroud or backstay connected to the mast, and dangle the other end in the water.   I'm not sure if this would REALLY save your bacon, but it might make you feel better, at least if you believe in the theory of grounding the mast to the water so that the mast doesn't develop any higher potential...

THEN, if you go with (a) and install a large grounding plate for lightening, you have to figure out if you're going to galvanically tie it to all the other stuff, to AC circuits, DC, the motor case, etc...

Again, the point is that there are several different issues going on here.  Lightening should be a significant concern for those of us out on the water - but it is a different problem than galvanic corrosion and electrical shock hazard.

On Tuesday, December 8, 2020, 10:23:19 AM CST, James Marcroft-Clark <greenlinepcs@gmail.com> wrote:

I know that Will Prowse who does a pretty popular DIY off grid solar channel on Youtube posted that he is looking into the lighting strike on sailboat stuff, so I expect there to be some good content on it at some point in the future. In my system, I am doing 12v via step down transformers, and there is no way to earth those, so those would be floating anyway. As the masthead is almost always the point that lighting strikes, and the wiring near there would be floating 12 v from the step down transformers, I'm wondering if fusing the 12 v on both legs would be enough. I was thinking about how e- travel in wiring from a lighting strike and wondering if it made sense to fuse at the masthead devices (lights and wind direction) on both legs, as well as fusing at the output from the step down transformers. I'm thinking that it probably would not be enough, as the electrical potential on a lightning strike is incredibile, and it would easily arc to other conductors on its path to earth. I know they make lighting arresters for this purpose for terrestrial applications, but I've little knowledge about these devices. In the fuse placement videos I've watched, I think the fusing is designed to prevent overcurrent damage generated from current flowing from the batteries to the devices and it protects wiring with a current flow in this orientation, but not others. That is why I am starting to think that fusing both ends of every wire may be the means for preventing, or at least minimizing, damage to the wiring and batteries due to sideflashes. I think in an actual lightning strike, every fuse would blow on its path to ground, but might spare the sensitive electronics. 

I did find this link with a wealth of information about protecting boats from lighting strikes. Tons of info here. http://www.marinelightning.com/science.htm I'm still digesting what it says.

I'd love to have an all DC boat, but that Dometic inductive cooktop is absurdly overpriced at around 500 USD, as are most DC appliances by Dometic. Also, it would take 4 of the 48v to 12v step down transformers I have wired in series to power it at a cost of over 200 USD. That costs more than my inverter/charger, and I'd have to still have AC for charging the batteries from a generator or shore power.  I'm just waiting for someone smarter than me to DIY a 48v induction cooktop and document it.

On Sun, Dec 6, 2020 at 2:07 PM THOMAS VANDERMEULEN <tvinypsi@gmail.com> wrote:

Keeping the 48 VDC system entirely separate (or virtually so) from both 12 VDC and any AC systems just makes logical sense to me.  And I don't disagree with your thought on fusing "both legs" (which I take to mean both positive and negative sides of the battery pack), but I'm still pondering the thought experiment of lighting striking an electric auxiliary sailboat.  Are you thinking that fusing off both sides may prevent or minimize damage in the event of a lightning hit?

If fusing both legs, what's your opinion on fusing both plus and minus of the cables between the on-board charger(s) and where they interconnect with the batteries (separate buses presumably)? 

I'm still thinking about a couple of further design points.  Trying to keep the 48 VDC and 12 VDC systems completely apart is complicated where a stand-alone 12 VDC battery pack is provided to drive boat accessories & instruments and also for battery monitoring and charger controller where the designer wants to avoid using the traction battery for anything except driving the motor.  [In my test-bench setup, I'm pulling 12 VDC from the traction batteries through a step-down transformer, but once installed and operational, I think driving the monitoring and charger control circuits from a separate 12v battery pack, as is done in automobiles, makes sense, though it does require an additional charger on board.]

And dockside, charging from shore power, the 48 VDC and AC systems are certainly connected through the chargers.

My setup is pretty simple, with no inverter, no generator, and no AC usage except while dockside.  Folks with generators, inverters, and lots of AC-powered conveniences have a much more complicated life!

[-tv]

On Sun, Dec 6, 2020 at 1:24 PM James Marcroft-Clark <greenlinepcs@gmail.com> wrote:

Thanks, good to know. Since I only saw it in one place and you got word straight from the horse's mouth, I think you're probably right. I think it still makes sense to make it a floating system, because of galvanic corrosion and the rest to those in the water in varying saline conditions. I think it's only a matter of time, and perhaps it's even happened already, that an electric sailboat will be struck by a lightning and current from the lightning bolt will reach batteries and cause a catastrophic failure. I think it just makes sense to follow the precautionary principle and fuse both legs.

On Sun, Dec 6, 2020, 09:08 THOMAS VANDERMEULEN <tvinypsi@gmail.com> wrote:

James:

I was quoting the ABYC standard when I stated that E-30 applies to 60 VDC systems.  Also, as mentioned, I had directly confirmed with ABYC that it would NOT apply to the 48vdc (nominal) system I would be installing.

[-tv]

--

Reagan Clark

" Do not be too moral. You may cheat yourself out of much life so. Aim above morality. Be not simply good, be good for something."   -Henry David Thoreau