Originally Posted by Alan Wheeler
Sorry I wasn't clear. I was refering to any current
that was flowing in the ground as being Galvanic due to two boats tied together via a cable. Because this current
is "normally" so low, the diodes effectively isolate that very small galvanic current.
I guess I should have mentioned this in my original post. Specifically, what Alan is talking about here is:
The voltage you get from galvanic corrosion
in sea water
depends on the specific metals involved, but is very low. The 1.4 volts was chosen as the lowest value that is sure to be higher than the voltage caused by the corrosion
. A single
diode blocking at 0.7 volts would prevent many types of corrosion, but if your neighbor happened to have a metal that is 1.0 volts away from yours, it wouldn't work. So we use two.
If your boat were sitting in sulphuric acid instead of sea water
, you could get a higher voltage. But then you would have far worse problems...
b.t.w. The voltage depends on the type and condition of the metals involved, but not on the surface area. Larger surface area can provide more current (more amps, and faster corrosion), but not more volts. This is just like your batteries, where a Group 27 and an 8D both put out 12 volts from the same chemistry.
The purpose of the galvanic isolator
is to prevent your zinc from protecting your neighbor's propeller
. It works for that. It isn't expected to protect you from bad marina wiring
or a short to ground inside your boat.