I just installed 2 Multiplus 12/3000 120vac in Split Phase and running the outputs of those through a 100a Autotransformer. The idea was to Balance the output off the 2 inverter/chargers. I have they system wired per the manual, tying the output neutrals together from the Inverters. The system works OK when NOT inverting. But once AC mains are taken away and the system is inverting, one unit shows negative amps and the other shows positive amps. All AC load breakers are turned off and still using just over 40 amps of 12vdc per the BMV-712. 
