Hi again.

 

1) Is it possible to create a UPS-like setup using a Victron Phoenix and a Blue Smart Charger connected  to a set of batteries? Or is this downright dangerous?

2) If possible, do you connect the 2 units to the same battery-terminals or better to use a busbar?

 

Thanks

-G-

Very much possible, just inefficient.

You would be doing double conversion the whole time AC-DC-AC.

This would also make your potential charging current pretty bad, let me explain.

Say your loads are 150W AC

You go and buy a 12/30 Bluesmart charger.

So now you have 30A of charging current, not too bad, except  you will use around 12A (150W / 13.5V =  11.1A But there are also inverter efficiencies to take into account) just powering your loads.

So only the remaining 18A can be used for charging, obviously this quickly spirals out of control as your loads increaase, if your loads are say 300W

You will be using 22A of the chargers 30A capacity only power your loads, and there will only be 8A left for charging.

If your loads are say 400W you would need the entire capacity of the charger simply to keep the loads powered, and you won't have any real charging happening.

 

1 hour ago, gallderhen said:

2) If possible, do you connect the 2 units to the same battery-terminals or better to use a busbar?

I would say go with a busbar because then you can easily fuse the connection going to the battery. 

You could make a UPS that use an automatic changeover switch which switch to the inverter as soon as the grid fails. This is more efficient that in the inline method described by PJJ, but will cost more and you need a fast switch so that appliances will not loose power during the change over.
Victron sell these (Filax 2), but they are expensive so it is better just to go with a Multi.

 

More detail on the transfer switch and wiring https://www.electricaltechnology.org/2018/11/automatic-manual-changeover-transfer-switch.html