I’m experiencing unexpected behavior when limiting battery charging via DVCC register 2705 in ESS Optimized mode, and I’m unable to share PV surplus between the MultiPlus-II GX battery charger and a solar diverter.
My setup is a MultiPlus-II GX with ESS Optimized, Pylontech 48 V batteries, DVCC enabled, and zero feed-in.
Using Home Assistant with a yaml script, I calculate PV surplus from 2 Fronius inverters and write to register 2705 the max system charge current to limit battery charging power. The remaining surplus should be consumed by a solar diverter connected to resistive load (for hot water). First I’m trying to test a 50/50 power sharing.
However the limit set via 2705 does not seem to be respected and the battery sometimes absorbs more power than expected !
Questions:
Is register 2705 the correct control point to limit MultiPlus-II battery charging power in order to share PV surplus with another load my solar diverter ?
Are there ESS/DVCC priorities or internal behaviors that can override or modify the value written to register 2705 ? I understand that near the top of charge last ~10% , battery charging power naturally reduce due to float/absorption behavior.
2705 is the DVCC system max charge current. Dbus service /Settings/SystemSetup/MaxChargeCurrent: indicating that it is a hard limit, and not normally adjusted. Yuo might want to look at : com.victronenergy.settings ESS max charge current (fractional) 2701 uint16 1 0 to 100 /Settings/Cgwacs/MaxChargePercentage
I’d like to clarify that the “Max charge percentage” setting is not visible on GX console when DVCC is enabled with a CAN-bus battery.
This makes me suspect that register 2701 is ignored when DVCC is active
However I’ll go ahead and run the test as soon as there is enough PV production… the current snowy weather doesn’t help me ( I’m not in summer on one of the Fiji islands ) but I’m not convinced this will solve my issue.
Changing the value of register R2701 (ESS max charge current in %) not solve the issue.
The PV surplus is not shared in a controlled way between the MultiPlus-II GX battery charger and the solar diverter :
Sometimes the charger takes almost all the surplus, and at other times the diverter does, especially when PV production fluctuates strongly the day after a storm with variable cloud cover and sunshine.
Interestingly, and without a clear explanation, when both devices are left to share the surplus on their own (i.e. without any YAML scripts enabled in Home automation system) a kind of natural 50/50 balance seems to occur, resulting in an acceptable surplus sharing…
But it is unfortunate that this sharing cannot be controlled programmatically with Victron equipement, for example via Modbus register writes, to make one device or the other proportionally priority.
It’s clearly not ideal to run 2 independent control devices at the same time based on the same control variable (PV surplus) especially when both devices have very different measurement and control response times. However, even in such a case, a software-based approach with appropriate filtering and anti-oscillation logic should theoretically be possible !!!
Has anyone already encountered this behavior ? or has any insight into this ?
You could use the relay assistant to switch on or off either relay or ac2out to control load to heater.
Not as controllable as a diverter, as only on or off for given voltage or soc.
Thank you for the suggestion, but my goal is a proportional and dynamic sharing of PV surplus between battery charging and a solar diverter. An on/off approach is not sufficient, especially with fluctuating PV production.
Both systems use similar thyristor-based power modulation : GREAT ! the main difference is their response time ! From a control perspective, it is unfortunate that the Victron charger power cannot be dynamically controlled via Modbus by a supervisory script to properly coordinate this surplus sharing.
At the moment, I simply let both systems self-regulate : sometimes the Victron charger absorbs most of the surplus, sometimes the solar diverter does, and sometimes they reach a rough balance 50/50. The outcome feels as if a crystal ball were somehow involved in the Victron GX control ESS logic Super ! Meanwhile, cold shower in the evening… The water heater only gets the crumbs while the MultiPlus-II GX takes all the PV surplus for the batteries.
I had a diverter in use for years with a sma ac coupled PV system, worked great.
Then when I added mp2 + battery, diverter & victron didn’t play happily together.
So I went aux relay control for immersion, worked OK, then I doubled size of battery to 32kwh and works brilliant as I have enough stored capacity to allow immersion to be on without worrying of high %drain of overall capacity.
Thank you very much for your explanation.
Could you explain how you implemented the on/off control for the immersion heater?
Specifically, did you use a Victron Relay Assistant or an external script/automation, and what were the trigger conditions (SOC, battery voltage, ESS state)?
I have to admit that I’m a bit frustrated with my choice of the Victron MultiPlus-II GX, as I’m currently unable to control it as flexibly as I would like for this type of PV surplus management.
I probably should have stayed with the inverter brand I was using before, which had always given me full satisfaction, but unfortunately was not compatible with Pylontech batteries…
( I’m not in summer on one of the Fiji islands 
) but I’m not convinced this will solve my issue.
Super ! Meanwhile, cold shower in the evening…
The water heater only gets the crumbs while the MultiPlus-II GX takes all the PV surplus for the batteries. 