question

Synchronizing the Inverter will be a problem because it has never been designed to do this.
Any sort of DIY hacks is just dangerous.
Your best bet is a MultiPlus because it will synchronize to the grid frequency and transfer from battery or grid seamlessly. The MultiPlus WILL NOT feed back if it has no grid code, it is "None".

Hello WKirby,

i am not sure if we are talking about same feed to grid. What i mean? So far i understand when the load is disconnected from multiplus and because multi is "connected to grid" (i do not know the right English terminology) as any hybrid inverter his big transformer energy can not disappear, as we all know, so it is fed to grid for short moment (few sinus periods). However energy meter from provider will register this and if you have no special "producer" contract it is illegal and charged. Could this be avoided by multi ? UPS like inverters has no such issue but of course they can not fluently take/draw energy from grid to help batterry/PV as hybrid can.

When you open the box and install the MultiPlus, it will behave just like a normal UPS.
The MultiPlus has a big bypass relay at the grid input. If this relay is closed then the MultiPlus will be a Charger only, it will only take power from the grid, like a normal battery charger or any type of appliance like a TV or welding machine. Your loads will only be getting power from the grid via the bypass relay. The Inverter will not be working, so the MultiPlus cannot put any energy back into the grid.
Only if there is a grid failure, then the bypass relay will open and then the inverter will run from battery. With the bypass relay open nothing can go back into the grid and loads will be powered from the Inverter.

The only way to cause the MultiPlus to feed back is if you change the operation with applying grid codes, "Assistants" and do some special configurations with ESS. In that case you also need to have the CCGX to make this work. Basically, you really need to do a lot for this to happen and you need to know that you are doing it.

From the factory, the MultiPlus is not allowed to feed back anything to the grid. It will work just like a normal UPS like "APC". If you would be happy to plug in a small APC UPS for your computer or whatever, then the MultiPlus will behave the same.
Synchronization is to provide smooth transition when changing sources - again, just like a normal UPS.

Perfect that sounds promising. I downloaded VE configure and played in demo mode (fake target). I would like to purchase Multi 800VA/24V. Please review if this would work with following conditions:
- LIFE battery 90A(future 180) with safe working range 3.1 - 3.40V/cell => 24.8 - 27.2V
- when the fridges start up they can draw >2Kw but after startup 240W/400VA
- to reduce inverter size i would like to compensate peaks by virtual switch (VS)
- no charging from grid (only solar charger), no overflows to grid

So if i understand everything right VE configure settings would be:
- TAB General -> Enable battery monitor off.
- TAB Grid -> Country none, Transfer switch Accept ... default box values, UPS on
- TAB Inverter -> Power assist off, DC Input shut down 24.8V, DC in low restart 27.0V, Enable AES ... hm probably not.
- TAB Charger -> Enable charger off
- Tab Virtual Switch -> Tab Usage Ignore AC input VS on = do not ignore; VS off = ignore, Invert no
-> Tab A: Set VS ON when load higher than 650W 0sec or when Udc lower than 24.8V, 10sec
-> Tab B: Set VS OFF when Udc higher than 25.0V, 0sec

Q: is there DC dynamic cut-of feature like in Phoenix VE.direct planned for multi ?

Q:Can i connect BMV (i have running it with raspberry with Venus) to also have SOC condition in Inverter tab ?