Opened a huge can of worms regarding galvanic isolators

[Ian MacAulay]

Afternoon.

Before posting this I've done extensive erasing with no real answer.


I have a small power boat with cuddy that I use for fishing and overnight stays in marinas. It currently has just one battery.

I know a fair bit regarding electrical systems but on distribution systems so boat electrics with galvanic isolators is new to me.

In the past I've just had a camping type hook up lead that I've used for overnight stays with built in RCD protection. I'm now adding to the boat a second battery on a split charge system so when out fishing I can run all onboard electrics knowing I've got a spare battery to switch over to if needed.

Having the camping type lead for a heater and bits and bobs for the overnight stays is useful, but as all my lights and so on run off the 12v system a long 12hour night may use up all my stored battery power in boat batteries so I'm wishing to install a sterling pro battery charger to keep all the 12v fully charged ready for the next day.

Now as I'm keeping the system simple and isolated from the boat with no real integration to the boats grounding system (apart from the negative charger supply)can I install a charger to supply both batteries and keep them charged and plugged in to my camping type hook up lead when in the marina or do I need to go more in depth and install a GI?


Secondly if I was to add a 12v -240v inverter to use while out and about on the water am I right in saying this would have no effect and is possible


Thanks in advance and I hope it all makes sense

Ian

 

[rafiki_]

You really need a GI. Your boat is always at risk from stray currents, and in marina's, not all boats are earthed equally. Some may have eaten their anodes, so their stray currents will be looking for yours. So safest way is to fit a GI. Have a look at E Bay, they are about £70 ish.

 

[Ian MacAulay]

Thanks.

With my planned system I'm crating no physical connection to the boats grounding system so therefore creating no circuit back through the water so do I still need one??

Thanks

Ian

 

[Alpha22]

I would think not, but I'm no expert. However, there is a connection between 240v earth and the -ve side of your battery. That being the battery charger. How much of a connection, I don't know.

Without the battery charger you will be totally in the clear... with it???? I'm sure someone else will let you know....

Incidentally I moor in a marina with 60 other boats and not one has a GI. Neither do we have any long term problems......
All on shore power, all with winter heaters... how many have earth bonded to -ve I would not like to guess, but probably very few.

 

[lpdsn]

Thanks.

With my planned system I'm crating no physical connection to the boats grounding system so therefore creating no circuit back through the water so do I still need one??

Thanks

Ian

The basis of needing a GI is that the mains Earth and Neutral can't be assumed to be at exactly 0V potential to the real earth (or rather the sea). If you have anything bonded to the boat to provide a ground, then you can get stray galvanic current between the sea and the mains Earth with your boat acting as an anode.

Sounds like you don't have that problem, but worth double checking. For example you may well have the battery grounded via the engine block, prop shaft and prop. Or via the engine block and cooling seawater.

So you need to make sure the charger isolates the 12V output from the mains input, so that the negative is floating. They should do, but it probably isn't necessarily a design requirement for ones intended for use ashore - e.g. car battery chargers.