Interesting Point of View From Nigal Calder

[_LifeInTheWild_]

I am interested in eliminating the need for a galvanic isolator and using shore power with little corrosion risk. Moving to an inverter based AC system seems to solve this according to this excerpt from Nigal's book Boatowner's Mechanical and Electrical Manual. I am wondering if anyone has used this approach and what the benefits/drawbacks are besides limiting your AC power to the size of the inverter and battery bank.

[Dsanduril]

I'm sure you'll get a lot of dissent, but this is exactly how our boat is wired (and I'd never seen Nigel's discussion before you posted it). There's an RCD right behind the inlet, the AC travels about 3'/1m to a fully isolated battery charger, ant that's it. All boat loads are supplied by batteries or batteries->inverter.

Using a universal input charger this gets rid of all of the 120/240V 50/60Hz headaches, although there is still a need for adapters. In our case we have a 230V shore power plug and a 120V. Each goes to its own RCD, and then to the battery charger (the only reason for this is the RCDs, when installed I couldn't find any that supported both voltages, haven't looked lately).

The down side is micro-cycling of the batteries (the charger we have cannot keep up with the maximum demand of the inverter) and the limiting of available power to the battery/inverter combination. In our case we don't really need any more power at the dock than at anchor, so it doesn't really matter. If you use electric heat or air conditioning at the dock you may find it limiting.

We've used this setup with no problems in 20 or more countries, but OTOH we spend so little time at a dock/with shore power available that we may not be a good use profile.

As Nigel notes, it is not ABYC compliant, so if that is important to you (or your insurer, or a surveyor, or.....)...

[BillKny]

I can't imagine what the reason for dissent would be. This is a simple and very workable system. With modern inverters you can easily set up a system where you would have 6kW of 120V/60Hz supply available onboard--or whatever other flavor of AC best fit your needs.

Our boat basically runs like this away from the dock, because we have a WhisperPower DC only generator. All of our AC needs come from a 3kW inverter. If we ever felt the need, we could easily gang up our inverter and have 6kW available, but we have never then dreamed up a scenario where we would require that. The 3kW unit even handles our AC needs on the very rare occasions we use it away from the dock.

The primary benefit of such a system over an isolation transformer is that it simplifies the use of various types of shower power (50/60 Hz and 120/220/240V) while keeping the supply on the boat the same.

There are benefits to using an isolation transformer too, and if I was not going to be traveling to areas with "hostile" shore power standards, that's the route I'd go, but there are good reliable choices on both sides.

Just be SURE that the battery charger you pick is actually fully galvanically isolated. Not all are.

[ilenart]

Thats similar to the system that was supplied by Hallberg Rassey for my boat, except the shore power run thru a isolation transformer, which can also step down / up the voltage. My charger / inverter is 115v only, however it can handle 50 or 60 hz. After that everything on the boat runs from the batteries, 12v direct and 115v via the inverter, except for the watermaker that runs off the whisperpower generator.

Ilenart

[Chotu]

This is exactly how I’ve done my system, except I haven’t got around to installing a shore power connection just yet.

[LittleWing77]

Originally Posted by BillKny

I can't imagine what the reason for dissent would be.

Originally Posted by Dsanduril

As Nigel notes, it is not ABYC compliant, so if that is important to you (or your insurer, or a surveyor, or.....)...

ABYC is the current marine safety standard in North America.

LittleWing77

[parachute]

If you don't fit a galvnanic islolator then you risk stray current corrosion which will destroy everything electrical.

[ranger58sb]

I suspect aircon and water heater would take a bit of thought...

-Chris

[Chotu]

Originally Posted by ranger42c

I suspect aircon and water heater would take a bit of thought...

-Chris

Absolutely.

In my installation that follows this logic, I just have a separate circuit entirely for HVAC (endless on demand propane hot water).

The HVAC stuff runs on its own dedicated circuit from the generators, but can also use a shore power input if required.

My AC input is complicated. Dual, non phase-locked generators, shore power, inverter.

In my somewhat complicated, but highly redundant setup, you select where you want house power from (inverter always unless an emergency/inverter failure).
Then you also have the opinion of selecting Generator A or Generator B, in case one of the generators is down.

We use electric for the oven, so that’s always a generator.

HVAC has its own input selection of Gen or Shore. (Although I didn’t put the shore leg in yet)

[BillKny]

Originally Posted by ranger42c

I suspect aircon and water heater would take a bit of thought...

-Chris

Chris,

You apparently do not understand the nature of the system, or the capabilities of modern inverters.

A shore power connection for a typical yacht of the size we talk about here is either 30 Amps/120V (roughly equal to 16 Amps/220V) or 50 Amps/120V (roughly 32 Amps/220V). This can be exceeded for very short periods of time for motor starting and such, but in general the continuous duty rating for these systems is 85% of rated load, or 26 Amps (3000 W) or 43 Amps (5000W).

This kind of continuous load is easily driven from inverters. If you wanted a buffer, you could install a 5kW inverter instead of a 30Amp shore power connection, or a ganged pair of 5kW units instead of a 50 Amp shore power connection.

The real beauty of the system is that you can use the batteries to fill in the peak power draws. We run two 8000 BTU AC units on a 3kW inverter without an issue. If we felt the need to run a water heater on the same system we'd have installed a 5kW inverter and all would be fine.

Of course you have to replace the DC power. so you need battery chargers at least equal to the average power draw of the AC system. On our 24V system this is easily done out of a 30 Amp shore power connection with a 100A charger. It's a beast, but it does the job. On a 12 volt system, a parallel pair of 100Amp chargers would probably be better.

There is NO reason you can't have your AC and hot water AND have an all inverter boat. None at all.

[Chotu]

BillKny is correct, but I chose to save a little on the cost of powering 30,000 btus of air conditioning from inverters. I wanted pure sine inverters so I made the compromise of generators for HVAC.

The cool thing about electrical systems is how versatile and flexible they are

[BillKny]

Originally Posted by LittleWing77

ABYC is the current marine safety standard in North America.

LittleWing77

LittleWing77,

I hear and understand, but here is how I see it (with corrections and discussion welcome!)

Whenever we talk about isolation transformers, the ABYC pretty much falls out of the picture. If we follow the ABYC standards, we can not install a real, functional, isolation transformer--and it makes no difference if that isolation transformer is built into a battery charger or is a standalone unit.

The requirement to ground the isolation transformer case to both the shore and the boat grounds effectively defeats the whole purpose of an isolation transformer. As far as I know, a fully ABYC compliant boat can not have a functioning isolation transformer, but must instead rely on a galvanic isolator with all it's foibles and issues.

I understand their logic, it's a risk assessment. This is one place where I use the ISO guidelines that my boat was built under.

So the original premise stands, at least as I understand it: If your alternative is an isolation transformer or an inverter powered boat isolated by the battery chargers, neither one is ABYC compliant, so the choice between the two can't be made on that basis...

[rslifkin]

ABYC is not law in the US, however, so unless a combination of survey and insurance forces total compliance, you're not required to follow it to the letter.



Personally, I wouldn't bother with a setup like this unless traveling to places with different, incompatible shore power configurations. But I also have a boat with 2x 50A / 120V legs, so it's a lot of power to deal with in a charger / inverter configuration.

[CharlieJ]

@BillKny #12:

The requirement to ground the isolation transformer case to both the shore and the boat grounds effectively defeats the whole purpose of an isolation transformer. As far as I know, a fully ABYC compliant boat can not have a functioning isolation transformer, but must instead rely on a galvanic isolator with all it's foibles and issues.

You don't have this quite correct. I think you conflated the characteristics of a polarization and isolation transformers. An ABYC compliant isolation transformer can be either a high frequency type (no windings), a more traditional, iron core and windings type or a toroidal format.

For the iron core and the toroidal format, there is a requirement for an electrostatic shield between the primary and secondary that is connected to the safety ground on shore.. The boat side safety ground is bonded to the neutral at the secondary and is therefore completely isolated from the shore safety ground.

Of course there are requirements for construction and testing in accordance with various regulatory bodies (UL, IEC, etc.).

[BillKny]

Originally Posted by CharlieJ

@BillKny #12:

You don't have this quite correct. I think you conflated the characteristics of a polarization and isolation transformers. An ABYC compliant isolation transformer can be either a high frequency type (no windings), a more traditional, iron core and windings type or a toroidal format.

For the iron core and the toroidal format, there is a requirement for an electrostatic shield between the primary and secondary that is connected to the safety ground on shore.. The boat side safety ground is bonded to the neutral at the secondary and is therefore completely isolated from the shore safety ground.

Of course there are requirements for construction and testing in accordance with various regulatory bodies (UL, IEC, etc.).

Charlie,

Thanks for the clarification.

Which manufacturers make an isolation transformer with the ABYC required shield for the shore power ground that is needed to separate the safety grounds and actually get isolation while grounding as the ABYC wants?

Victron says they are NOT ABYC compliant, I assume because their toroidal transformers do not use this type of shield.

Mastervolt, I am not sure of, but since they do not claim to be ABYC complient, I am guessing not. Others I don't know...