Ketil Greve wrote:Having had big problems in my harbour with the zink anodes being eaten at an alarming rate in Edmond Dantes, I choose to dig deeep in my wallet to get a dividing transformer in Marie G. I only have a small zink anode on the drive leg, and that looked quite healthy when I took her out for cleaning. Expensive and heavy (15kg), but efficient.

It would be interesting to measure the potetial difference between the Mains Ground and the Boat's Ground...    (BTW, I spotted you on the fjord today...)

Arne

Stavanger, Sat

I checked the link to Safeshore Marine. They don’t tell what is in their boxes, but it would surprise me if it was not just a number of diodes. It seems that they have doubled the voltage barrier, probably by doubling the number of diodes in series in each direction. The reason why they speak about 1.2volt and 2.4 volt barrier instead of 1.4 or 2.8V is that a diode starts leaking current through at only about 0.6V and is fully open at about 0.7V.

The indicator LEDs which starts glowing at around 2-2.2V are probably just put in parallel with the big diodes.

Anyway, this version of galvanic isolator with doubled threshold sounds good to me, although not cheap. Just for the interest, I would have wired up two easily accessible test-points connected to each end of the galvanic isolator. When connecting to shore power in a new harbour, I would then be able to check the difference of ground potential ashore and on board with a digital voltmeter. If the LED starts lighting, current will be flowing, and I would avoid staying connected to shore power for long.

Arne