If I were to install 2 Multiplus 2x120 units. Could they operate in 240 without AC in. So could one be primary for L1 and one be primary for L2 but out of phase? And thus when a 50Amp service was plugged in both units could charge the battery?
It seems like I could do this with the non 2x120 model, but if one multiplus were to fail then I could only power half of my system at least until I rewired both sides to the same 120 and then everything would be on 120.
Couple of things…
First, if you are going to wire and configure for 240 split phase you can do that with the 1 x 120 units.
Second, regardless of which units you go with, if one of the inverters go down, they both go down. In the case of the 2 x 120 if used in parallel (not split phase), you could reconfigure to stand alone in a few quick steps. However the 2 x 120 will only provide split phase 240 when connected to a 240 split phase input.
Since you mention the 2 x 120 I assume this is for a north american mobile installation.
It is possible to use the 2x120 as a split phase 120/240 configuration, it is just a waste of the extra switchgear inside the unit.
like mentioned, each individual unit is only able to pass through split phase power it cannot invert it. If you were to use a pair of them in split phase configuration you can of course pass through as well as invert split phase, and in the case of a failure you can still rewire/reconfigure to pass through split phase and invert single phase 120 to keep the 120v loads powered
Around here there really isn’t a whole lot of difference in the price of the single phase and 2x120 units, but if you are on a tight budget I would just stick to the single phase units. In the case of a unit failure you can just as easily rewire to pass through split phase shore power anyways