question

The schematic You attached does not represent a split phase solution. the 240v would be a european style 240v with one leg grounded and in that case common to the neutral of the 120v

If you are Only driving a small pure 240v load this is not a problem. But if you need a split phase with the neutral being the middle of the 240v then it would not work. You could however use a step up transformer with proper windings to achieve your goal.

Also if you are planning to be off grid beware that transformer are very bad when they are not in use. Their steady off load current is high 2 to 3% of nominal load for the best case up to 10% worst case.

I think you would be better off using a second quattro connected in split phase.mode.

My next "phase" of switch over from on grid to off grid is planned to reduce/eliminate SPOFs (single points of failure). To that end, I am planning on a second Quattro, MPPT controller, battery bank, PV strings, etc. That way if a component fails my PV system is not completely down. I may have to "limp" along until the defective component is fixed or replaced, but I won't be totally without power. I was hoping the autotransformer would address this for my 240V circuits. If a Quattro failed, I could move the autotransformer to the other Quattro. But, as you pointed out, this doesn't give me the US-style 240V that I was hoping for.

So, if I have 2 Quattros connected in split phase mode and one of them fails, then I have no 240V capability. I am looking at reducing the number of 240V circuits, but I can't eliminate all of them. Are there other SPOF mitigations for the 240V circuits?

You are correct on the SPOF Approach. Transformer are much more rugged and less likely to fail. No question about it.

As I mentionned your solution work. If your loads are strictly 240v then they do not care that the unit is grounded on one side.

To have a split phase if you use transformer you need to use a transformer with 120/240v primary and 120/240v output double windings. Connect the primary windings in parallel and the secondary in series. Ground the mid point of the secondary.

It is too bad that you already have a 120v quattro.

The solution often used in the marine industry is to use a 240v quattro and an auto transformer on the output with middle point grounded. You must disable the quattro ground relay. On the input if you connect to the grid or a generator do not connect the neutral. only the two phases.

The advantage is that most of the time the big loads are 240v so you can use a smaller auto transformer.

The reduction of the SPOF however comes at the price of system efficiency. If you have enough generating power (solar/wind generator) you may not care. But a 5kW auto transformer will have a 200 to 500w continuous load which will cost you 5 to 12kWh per day... Is the SPOF protection worth that much...

When I started down this path, I saw that 2 Quattros could be configured in parallel (split phase) mode to provide 240V as well as provide redundancy (eliminating SPOFs). However, I'm now digging more into the manuals for setting up a parallel Quattro system. I'm seeing this warning:

"Parallel and Multiphase systems are complex. We do not support or recommend that untrained and/or inexperienced installers work on these size systems."

OK, so I'm not a professional. Does this mean I made a bad choice going this route? Am I totally on my own setting up a Quattro parallel system?

tBratten,

Multiphase systems are definitively more complex and if you do not have a very good understanding of the basic of electric system including safety requirements then I strongly urge that you find a professional in your area that can help you.

The beauty of the Victron system is that extermely large and complex system can be built but they are many pit falls that can lead to serious problem and risk of injuries.

Setting up Split phase system with two units is on the lowest scale of the difficulty but you should work with a Victron professional.