The eu6500is has two inverters. When running in 120 volt mode they're in parallel, and in 120/240 volt mode they're in series. With 50 amp service the easiest thing is to run 120/240 volt mode and plug the rig into the 240 volt outlet using a suitable adapter. If you can't run both air conditioners and it's just over the edge, you could maybe find success running in 120 volt mode which would take fiddling with the wiring. In either mode you have the same total power available. In 120/240 mode it's split evenly into 2 "buckets" where you might overload one but have some available in the other. In 120 volt mode all of the power is in a single "bucket", giving a bit more flexibility in how it's distributed.