question

I forgot to mention I also have a BMV712 Smart monitor.

An auto transformer has a single winding with multiple taps to adjust input to output voltage. It does not isolate the output from the input.

To do what you want, you need an isolation transformer with multiple taps on the input winding to accommodate world voltages. The secondary (output) winding would always be set to 120 volts.

Are you certain isolation is needed? I know nothing about boat electrical requirements so don't take this question as and indicator you don't need the isolation.

Hi Kevin, and thank you for your input.

I think the issue is a little more complex than voltage differences as some countries (particularly Europe) work on 50Hz instead of the USA 60Hz. I want to be able to handle any AC source (ignoring plug and connector differences) without frying my AC appliances.

I have a gut feeling that I will need to transform the source to AC 120/60Hz and then Isolate my boat from the source with the two windings. I just wondered if there was an easier solution?

I am a bit limited with space and a little concerned about the extra weight of both transformers, but if I have to go this route then so be it.

Frequency of shore power MAY create additional design challenges. Most electronics and heater type loads will be OK on 50 or 60 Hz but if you have motors they will most likely (but not always) require 60 Hz.

It's not simple to deal with 50-60 Hz conversion. One way to do this is to use the Multi as an inverter only. Shore power would not connect to the Multi input. You'd need a separate charger to run off of shore power and this would be the only item that needs to handle multiple voltages and 50/60 Hz.

If you go this route, consider a Phoenix Inverter (no AC input) to save some money.

The inverter need to handle all loads as there would be no pass-thru or assist. Your battery bank would also need to be large enough to handle peak loads on its own (maximum amps from the battery bank) as well as maintain power to the loads (AH rating of the bank) without assist from shore power.

The size of the charger depends on how fast you want the battery bank to recover its charge and/or if you want shore power to handle all loads without drawing down the battery bank. I would personally allow some battery draw-down on peak loads as long as the shore power, alternator and solar can keep up with average loads.

The good news is that the charger could be less cost, smaller and lighter than transformer(s). For example, a Phoenix 50 amp/12 volt charger accepts 90-265 volts 45-65 Hz and weighs 8 pounds. 50 amps @ 12 volts is 600 watts. There are smaller and larger Victron chargers also. Compare that to the Victron 3600 VA isolation transformer at 50 pounds!

You also mentioned charging from the alternator. I suggest something like the Orion DC to DC converters. An alternator doesn't always make the best house battery charger because it has no way of controlling charging current. The battery isolator is only a switch.

Another complication is charging the starter battery from the house electrical system. This requires power from in the opposite direction but may not be necessary depending on where loads such as anchor lights, winch motors, etc. are connected (starter vs house).

Question:

Will a Victron Orion 12/12 Volt 30 Amp 360 Watt, allow flow in both directions ?

FROM / TO: House LITHIUM Batteries: 4x 228AH @ 12.8V

And

FROM / TO: Starting LEAD Batteries: 2 x 60AH @ 12V (2 alternators 60A 12V

I am concern with the huge size disparity between Banks.

(As additional Info the Li Batteries are feed from 2 MPTT 150/60A-12V and a inverter-charger Victron Easy Plus Compact 70A 12V 2600 VA)