Let me explain again why galvanic isolators for boats are not fool proof and, IMHO, should be outlawed;
These devices are using a side effect of a diode called the junction voltage. Here is the V-A graph of a diode:
In the top-right quadrant of the graph we can see that the diode only starts conducting at roughly 0.6V. Below that voltage, the diode is not letting any current
Now here is the problem; galvanic corrosion
from shore power
connections is caused by a DC current
that travels through the ground wires of at least 2 boats. The shore-ground connects the boats and the circuit is completed by the water
touching underwater metals of the boats. This means it takes two to tango and whenever this problem pops up, both are to blame. This alone means the OP has no chance in court.
Now, AC is alternating current, meaning the direction changes 50 or 60 times a second. Diodes are like check valves, only allow current to travel one way. But we can connect two diodes anti-parallel which means they are parallel but in different directions. When AC flows through this, one diode passes the positive parts
of the waveform and the other does the negative parts
So, we pop the anti-parallel diodes into our ground wire circuit. Now, if the voltage over the diodes becomes 0.6V or more, they start conducting providing the safety
which is the reason to have this wire. But if it is less than 0.6V, there is no current possible which means a small DC current is blocked and galvanic corrosion
prevented (also on the other boat!)
Now here is the catch... if the DC potential is more than 0.6V, then the diodes start conducting and the corrosion happens anyway, like if we don't have this protection just as the problem gets worse and we need it more! Frak! So the manufacturers and dealers and installers who want our money
had to solve this and came up with putting two of these diodes in series (each way so total of 4 diodes) which doubles the voltage potential needed to 1.2V. Okay, so now it works for a 1V potential but what if it gets really really bad like 1.3V ? Well, your boat starts bubbling then because the protection is ZERO. Go up to 3 diodes? Remember that the ground wire was supposed to provide safety
against electrocution which is already reduced by these diodes and 3 in series for 1.8V potential was simply denied by the local codes. So, protection is only up to a 1.2V potential over the ground loop.
Now all the GI fanboys will start whining but hold on, I will make it worse first before addressing their arguments;
Ever heard of a diode burning through? I do, like in a diode bridge or on an alternator
. Diodes tend to burn up now and then. The reason is that same pesky 0.6V potential over the diode... it stays there when the diode is conducting. This means that when 10A of current passes, 0.6 * 10 = 6W of power is dissipated as heat inside the diode. This heat dissipation makes them burn through.
Now, if diodes in a GI burn through, what do we have? Exactly, a life threatening situation!
Okay, the GI fan boys will start talk about modern designs with capacitors and alarms etc. Alarms sound when your AC installation
is lethal, very nice. What happens when that alarm
circuit fails? Ever seen lightning
strikes around boats damage equipment
? The whole thing is like a time bomb.... and when the problem of galvanic corrosion gets really big... it completely fails and let your boat or it's metal parts corrode away like crazy.
I understand that many don't exactly know what an isolation transformer does. It's primary use is as a personal safety device. The output of the transformer is floating, not referenced to ground. This means you can take any one lead in your hand and touch the water
with your other hand and nothing happens. If you do that with the hot wire from a regular shore power
connection and a GI installed you die. A GFCI type of device would protect you in that case (a breaker doesn't) but it's not needed with the transformer. Only when you touch both wires out of the transformer you can get a shock. This is very safe and the reason that electronics
workbenches have an isolation transformer to protect the workers that repair electrical appliances
Second thing with the isolation transformer is that because it is so safe, you are not required to use the ground wire on the secondary side of the transformer. On a boat it means that the ground from shore protects your shore power cable, inlet and internal wiring
to the primary side of the transformer. That is where that ground wire is stopped, it doesn't get connected to anything else aboard. This means you are protected against any level of galvanic corrosion caused by shore power systems, not just the easy ones where the galvanic isolator
The GI fan boys will also tell us that these transformers weigh 200-300 pounds and cost $500 - $1,000 etc. In reality, a Victron 3.6kW transformer weighs 23kg which is about 50 pounds and a 7kW version weighs 28kg which is say 60 pounds. The 3.6kW is $780.- and the 7kW is $850.- so at least they get the price
Don't forget that a GI for 50A service
will also go up to $300.-
The only question is about the price
; how much are you willing to spend on safety for the boat and the personal safety of the people aboard. I find the $500 extra for the transformer money
well spent, can't think of many other things where it counts as much.
Okay, I'll make room for the nay sayers now