Originally Posted by goboatingnow
You will never get an answer to that or the stock answer is No , it will not. As itdepends on the internal design, even if it was a fully isolated output stage it will never be rated to act as an isolating transformer, even less so as a marine
This is not the way to go if you want the benefits of a proper isolating transformer( which you want becuase its primarily a SAFETY
Actually, it turns out that A/Sea systems makes a device which is exactly that, a AC -> DC converter and then a DC -> AC inverter
to convert from any type of power to any other type of power. They specifically note that due the the "galvanic isolation" of the device that it performs the same function as the isolation transformer by design and is intended to be wired that way.
I did get a "we think so" but want to check with the engineers from the Victron folks so it is possible I might just get an answer in the end
The safety is the primary feature but an extra 200 lbs of transformer if not needed is not my idea of fun.
The isolation transformer installation
requries bringing power (either neutral + hot in europe
or L1 + L2 for 240 or 208V US) and the safety ground aboard to the transformer. The guts of the transformer are connected to shore safety ground, the shield is connected to ships ground, thus breaking the galvanic connection to shore power while providing a proper safety ground by either connecting Neutral (230/240 single
phase) or the center tap of split phase from the transformer to ships ground providing the return path to a short circuit.
Now, in the case of the A/Sea systems equipment
(which is essentially a charger followed by an inverter) the wiring
is the same with no connection between shore safety ground and ships ground.
So, the hope is that Victron's or Mastervolt's battery chargers provide isolation in much the same way. (the inverter
does not matter as it would be the same when disconnected from shore power). Neutral + Hot or L1 & L2 are brought aboard, with safety ground (three wires), come through a dedicated shore power circuit breaker (three pole or should it be 4 pole, i.e. should you trip ground also, perhaps not...) and then a dedicated GFCI then to the battery chargers.
Just like an isolation transformer, it would be prudent to conduit the power from the shore power inlet to prevent chafe in the power feed and then a short to ships ground (but an isolation transformer has the same problem), then place the battery chargers in a dedicated locker which has no metal components. The battery chargers safety ground is connected to shore power safety ground. The battery chargers output is connected to the 24V DC bus for the boat at the batteries with dedicated fuses
Now, the potential issues I see...
1) When out of the water
it is necessary to provide a jumper to connect ships ground to shore ground or else the metal of the boat may float at some random voltage.
2) If the DC negative output cable chafes through to the battery charger safety ground (for example the case) then the isolation is compromised. No safety issue here just the galvanic protection is no longer provided and corrosion
3) Safety ground from shore power is applied only to the battery charger and thus most likely the metal case. If the shore ground is mis-wired this would result in a hot case which would not trip the circuit breaker (this can happen with a "normal" safety ground to ships ground connection in fresh water
as the return current through the water is often low enough to not trip the breaker, not sure if it could happen in salt
water). Reverse polarity is not an issue in this case as the charger can use a neutral and a hot or two hot leads (for the "normal" safety ground connection reverse polarity can be a huge issue as most of the circuit breakers are often single
pole leaving equipment
energized even when there is not a completed circuit).
So, if the battery charger case isolated from DC Negative AND from shore power safety ground (My Freedom 20 inverter on the last boat was this way) then you simply hook case ground to ship ground and there is not an issue.
If the case is connected internally to DC negative (unlikely, this is basically not a "galvanically isolated charger" as I understand it) and shore safety ground is used internally then we are good to go.
If the case is connected to the shore safety ground connection internal to the charger then there is the potential for an issue.
I think it will depend on the choices they made for the internal circuitry, i.e. when and how in the circuit do they step down the voltage.
Of course I could use "galvanic isolators" and connect shore ground to ships ground and then everything is fine (provided the shore safety ground is within the blocking voltage of the isolator) or else we get corrosion
If it were not the weight, space, and hum of the isolation transformer the belt and suspenders approach is appealing, however, if the battery charger is already doing the job then I will avoid it.
Thanks again for your thoughts, I appreciate everyones thoughts to help me avoid some corner condition I did not think of