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Old 28-09-2012, 03:37   #1
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Join Date: Aug 2008
Location: Depends
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Galvanic Isolator

OK - I guess after having a Galvanic Isolator on the boat, and having it live in the background, now I am forced to understand it better. Of course a Galvanic Isolator detects stray current in order to avoid unintended galvanic corrosion.

Our's has always been fairly quiet, and when it did go off in the US we were usually able to determine that there was some current from a nearby boat or a problem with the wiring at the marina.

Now we are in the Med and in order to have electricity we had to buy a 220 to 110 converter. It works fine, but since we have been using it the Galvanic Isolator will alarm periodically, on average maybe once every hour or two. The zincs appear to be fine and not being dissolved.

For the first time or two we thought it was indeed stray current from another boat or a faulty wiring scheme from the marinas we were plugging into, but after it alarmed at several different marinas we dismissed that idea.

Do any of you electrical gurus know what type of problem solving I should do?

When looking at the GI interface it is usually green, but occasionally it will flash red and appear that some current is interfering. Maybe it has something to do with a difference in grounding in Europe, or perhaps it is not able to handle the conversion from 220v to 110v.

Any ideas or comments will be appreciated!

Perplexed in Italy
The next best thing to playing and winning
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Old 28-09-2012, 09:26   #2
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Join Date: Dec 2003
Location: South Carolina
Boat: Philip Rhodes Custom
Posts: 387
Re: Galvanic Isolator

Is it a galvanic isolator or just a monitor?

Make sure that with the voltage conversion and changes to the boat that it is still in the ground circuit. If it is an isolator the ground lead from shore power should be connected to it and nothing else, and the boat ground should be connected to its "output". If you remove the boat ground from it with shore power disconnected, you should measure no voltage and greater than 100,000 ohms between the shore power ground and anything else ie. boat ground, shore power hot and/or neutral wires.

Having checked that, measure the voltage across it with the boat on shore power and normal loads. In particular any battery chargers should be running. Measure the voltage for both DC and AC voltages.

If both voltages are exactly zero it has failed.

If the DC voltage is above about 1.2 volts it has failed.

DC voltages between these limits are normal but should be below 0.75 volts typically.

If the AC voltage is above about 0.5 volts you have some AC leakage on the boat. AC leakage does not directly cause electrolysis but if it is higher than 0.5 volts it is decreasing the ability to block glavanic currents up to as much as 50%. Trouble shoot AC leakage by turning off everything one at a time until you see it drop, that is the device that has leakage and needs repair although some have built in leakage than can't be eliminated.

If you can't correct the AC leakage you can fit a Galvanic Capacitor. See the article on how they work at Galvanic Isolator Capacitor
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