Galvanic Isolators (again, sorry)

[VicS]

>This (as usual) is absolute nonsense. You clearly do not understand how a GI works. How can he possibly install one when he does not have a 240v supply in his boat?

The OP said "we plug in when we are in the marina on board to trickle charge the batteries whilst we kip on board overnight running the fridge etc". So it is you are talking absolute nonsense. If he uses shore power even occasionally he needs a GI on the earth of the cable he uses.

From the things he has said it is clear that he has no fixed shorepower installation. He just uses a portable charger plugged into a shorepower lead. By chance exactly the same model of charger that I chose to show how how to test for any connection between the plug earth pin and the negative output clip.

As my reading demonstrates there is no connection, obvious anyway from the fact that as Roger observed it only has a twin flex mains cable.

Therefore no GI necessary .

Even if he had a fixed shorepower connection there would be no real need need to fit a GI if the boat is only occasionally plugged in to the shorepower supply, It is only needed by people who leave their boats connected, even if the shorepower is not in use, for prolonged periods

 

[rogerthebodger]

>This (as usual) is absolute nonsense. You clearly do not understand how a GI works. How can he possibly install one when he does not have a 240v supply in his boat?

The OP said "we plug in when we are in the marina on board to trickle charge the batteries whilst we kip on board overnight running the fridge etc". So it is you are talking absolute nonsense. If he uses shore power even occasionally he needs a GI on the earth of the cable he uses.

Have a read at my posting #6 on this thread

http://www.ybw.com/forums/showthread.php?456670-battery-and-shorepower-(unrelated)-questions #6

 

[tri39]

I've read all the above and understood as much as O level physics allows. I use the same Ring battery charger as the original OP, but only connected for short periods in summer marina. Power lead disconnected all winter. On lift out in June the shaft anode had gone completely and one of the rudder skeg bolts was hollow and nutless!
I thought I'd understood that I don't really need a GI.
But Safeshore say
"Hi David, It,s always difficult to diagnose rapid loss. Are the main
anodes of sufficient size / composition and well connected? Have they
also deteriorated leaving the shaft anode to do all the work? It may be
a d.c. leak on your own boat or a leak on a neighbouring vessel.
Unfortunately very rapid loss can occur if D.C leakage occurs nearby and
finds its way down your power hook up lead. Our model GI70 sm with
remote status monitoring can often help to diagnose leakage problems and
obviously will stop galvanic corrosion via the hook up lead whilst ever
the lead is plugged in. Hope this helps"
I was going to ditch the charger but seems unecessary. I'm stilll undecided about wheter GI will help. There was a large gin palace nearby with lots of electrical toys, if not AC etc.
Can currents flow thro the seawater or do they have to arrive via the mains earth?

 

[Tranona]

Shaft anodes are relatively small and erosion can vary from year to year.

The skeg bolt is likely to be stainless and the corrosion will almost certainly be crevice corrosion rather than galvanic. Replace the bolt and nut with 316 stainless and liberally coat both the bolt shank and thread with sealant to keep water out and it should be OK.

 

[PaulRainbow]

If there is no connection from the mains hookup to the 12VDC systems then it doesn't matter how much leakage tries to make it's way down the power cable. It can't get to your underwater gear.

That said, you do need to make sure the battery charger isn't making that route available. Post #4 covers that.