question

Give it a go and please advise the out come as others may like to know.

you are doing stuff thats not that common so you may have to just try and see the result.

I tried and no issues observed in 3 hours of operation . Reset the system back to offgrid till I find more time on weekend

Of course the export to grid was not allowed so ESS only managed to feed the load and then throttled back the PV Also the grid was present at the time

I am using 1.5 KWp 150/45 bluesolar with single phaseMulti 800/48/9 with 10 KWh Lifepo4 battery with cheap chinese BMS connected to 5 x 3 KVA Quatro with 10KWp solar ( Smartsolat and fronius with 10 KW PRO BYD

Things yet to try and frankly too afraid to risk unless some clear examples or guidelines available

1. Disconnect the grid and see the behavious of Downstream multi - essentailly will LOM consider impedance of Quatro as grid or go into overload and disconnect

2. Allow export of the power from multi - with grid - I see no major issues as the house load is much higher than ~600 watt the system can feedback

3. Allow export of power with no grid and no load on Quatro to check safety interlocks

a. PV inverter assiatnt in quatro to check if multi disconnects on 53 HZ ( not happy with solution)

b. extenal conactor on input of Multi to disconnect from quatro when SOC of main abttery is higher than 95 % ( Reliable and tested with a APS 1000 Watt inverter) but then multi works in island mode most of the time

Thanks for the reply, can you give me some more details about the loads you have connected and how they are connected ?

I've been running a tiny victron-ess (800 Watt multi + 3.5 kWh Battery) behind a fronius hybrid and a 12 kWh BYD Battery. (As UPS for my Serverrack)

It works to some extend, but requires some data manipulation to avoid batteries feeding each other.

For the first battery in the chain, the second one will just be a load. So it will provide power to that battery whenever possible.

So, the nested battery requires manual orchestration on when to charge and when not.

For two ESS, you ofc. Require a second cerbo at first. Both systems need their own bus / bms / state.

I've then manipulated the smartmeter readings for the "inner system", so that the phase 1 readings just showed the loads actually attached to the chained inverter. This way, the inner battery was able to only supply it's direct attached loads. Also this system needs to be configured to balance in individual phase mode, else both batteries will take influence on the smartmeter reading and continiously fight against each other so to say.

I've posted my experience and stuff over here:

At first, i used a shelly plug as "subsystem meter", but later switched to a script, manipulating meter data on DBus.

https://community.victronenergy.com/questions/276783/ess-as-subgrid-fronius-hybrid-with-byd-battery-pre.html

It seems complicated. My only reason for doing it is to to be able to use two completely different batteries but maybe there is another way ?