Good day all!
I am running an experiment on my off-grid installation.
Components in system:
- 2x Multi-II 48/10000
- 1x Fronius Primo 8.2-1
- BlueNova Lithium battery bank with BMS.CAN connected for DVCC
- MPPT for direct DC charging connected via VE.Direct
- CerboGX
Reason for experiment:
Try to get a “small” generator to work much more efficiently and prevent it from disconnecting constantly due to load changes etc.
Ideal setup would be:
- Main inverter set to ON
-
- all loads connected on Main inverter as well as the Fronius Gird Tie.
- Charging inverter set to CHARGE ONLY.
-
- AC Output NOT connected, only AC Input to generator.
Reason for above setup is to keep the “Charge Inverter” as much isolated from the mini grid as possible, so that it can be a backup unit should we lose the main inverter due to possible surges. (We get regular heavy thunderstorms).
Initial problems faced:
As soon as the VE.Bus network has more than one standalone inverter, both inverters shuts down.
This was a bit of a surprise - as both inverters are NOT setup as parallel therefore should not assume outputs are bonded and should shutdown.
After the first problem I decided to program both as a parallel setup - however some more problems surfaced due to the un-bonded input:
When both inverters are set to ON - and only the Slave inverter (In this case the “charging” inverter) is supplied with AC input, it does NOT charge.
Setting the slave inverter to CHARGE only mode causes the Master inverter to shutdown.
What I have done now:
Both inverters are back on standalone mode.
Main inverter is connected to the CerboGX with ESS configured as it should.
Charge inverter is NOT connected to CerboGX and acts as a “dumb” charger without any DVCC.
This results are impressive charging performance from a “less than ideal” generator.
Input limits are easily maintained as loads do not interfere. (No need for power assist or dynamic current limit)
AC output stays pure as can be as the loads are not directly connected to the generator.
The Fronius now performs at full capacity and is not negatively affected due to “weak” generator input (It constantly disconnected before).
This results in a “True online double conversion” setup - no more lights flickering when generator works at high load.
My biggest problem now:
I would love to see the Charging Inverter be connected to DVCC and honour the BMS instructions.
What is next:
- I can hope to have the software allow the two VE.Bus inverter chargers to co-exist in some way. I cannot see that this will be an “unsafe” situation to allow this.
- Otherwise I would try something different: Work with the CAN network.
The CAN network idea:
I am not sure if this is possible but perhaps I could add a second CerboGX and extend the BMS.Can network to this CerboGX as well.
The Charging inverter will then be connected to this secondary CerboGX - so that I can have remote access, set input limits, etc. It will then also see the BMS instructions for DVCC.
The limitation of this is obviously that the DVCC is not really interconnected as for example the charge limit reported via BMS is 100A then both “systems” will push to 100A and then result in 200A charging.
Luckily my generator is not that big to cause overcurrent charging that easily - and I can have the generator cutout at 80% SOC before the BMS would lower the charge voltage after absorption.
There are many ways to skin a cat - so far this worked with amazing results - just hoping to get real DVCC working…
Thanks for reading!
Any advice / ideas welcome!