Size weight and cost:
Transformers are big heavy and expensive so on that basis they lose.
Reliability:
Other uses:
Summary:
Additional information:
5 Comments
Paul
"As the currents that cause corrosion are almost always less than 1 volt " That's an interesting measurement unit for current. -P-
Lou Reynolds
While I agree with everything you said in your description. You should point out that isolation transformers block both AC and DC stray currents. While it's a given that DC stray currents are the worst offender when it comes to corrosion, AC stray currents cause corrosion as well. But the main point of a isolation transformer is to prevent electrical shock hazards and the Galvanic Isolator is not designed for that purpose. The only thing a galvanic isolator does is block DC stray current.
Simonosteopath
"As the currents that cause corrosion are almost always less than 1 volt the protection is achieved, while the diodes still allow higher voltage current to pass in the event of a fault. " Shore earth and neutral are often several Volts difference and shore earth often many Volts difference to the water itself. Surely this presents a problem for a galvanic isolator?
Peter Kennedy
The shore ground and shore neutral are connected to each other at the power source (the transformer on the dock) They are not supposed to be at a different potential to each other but it is possible that if there are bad connections in the system or if you are at the end of a long dock on a hot day when all the air conditioners are running there will be a difference between them due to voltage drop in the neutral. You are correct that when this happens the galvanic isolator will conduct for part of each cycle.
Ann-Marie Foster
Metal boats, aluminum in particular, have a built in voltage to salt water as high as 0.9 volts. This leaves only 0.3 volts protection remaining. The ground connection in docks can be 10 times this amount, typically due to mis-wired boats using the ground connection instead of the neutral. AC leakage can easily exceed the traditional protection this so on each 1/2 cycle DC will be passed through the isolator and cause electrolysis. You should use a 2.5 volt isolator. Search Google for "2.5 volt galvanic isolator".
Peter Kennedy
That's a very interesting comment, thank you for bringing that up. Most aluminum boats I have come across have had an isolation transformer. I took a look at some of the Galvanic Isolators on offer for aluminum boats and it seems that none met the ABYC requirements of either being 1) Self Testing or 2) Fail Safe