We have installation with 3-phase setup with multiplus-II and RS 450/200 with three solar arrays connected with total Wp over 10kW. There is 280Ah battery with JK-BMS connected which the inverters are able to use just fine and it is visible on Venus OS. It is sunny outside and the system provides 31W of solar power. How can this be and what could be the possible reasons MPPT chargers do not charge batteries or provide energy to inverters? There is plenty of load as well to dump the energy to, but no…
Pls check your BMS settings. Pack full or absorbtion voltage is quite high. I recommedn 55.2V (3,45V/cell), not 56.8V.
Float voltage can be increased to 54,4V (3,4V/cell).
Andi Offgrid Garage on YT provide many information about BMS settings.
Pls select JK-BMS as battery monitor fix not auto.
You state using DESS.
Where are your loads connected? AC_out only?
Do you have a connected grid meter?
What is your SOC?
Are you importing/exporting energy while charging 31W?
Are you drawing energy from battery, while MPPT is limitied .
Do you permit exporting to grid?
What is your buy price vs sell pricse?
Thanks for the input. I tried to increase the voltages in the MPPT in effort to get the MPPT not limiting power due to voltage (even though based on the values it should not have been the case). Have to see about the BMS setttings. The electrical layout is a bit funny in this system. There is VM-3P75CT monitoring the AC input on the house grid connection. Multiplus setup is such that there is no loads connected to the output. All DC (Solar included) should be pushed to input. This setup did work better before but then the BMS had to be changed and since then the solar output has been very very limited. I have to go over the BMS settings once I get in bluetooth range of the BMS. BMS parameters say now that CVL is 53.6 but the battery is full at the moment (forced with setting ESS mode to “keep batteries charged”). I did change the BMS statically set to JK-BMS, no help yet.
In VRM dashboard I see Load side correctly what VM-3P75CT is seeing. There is load (2-3 kW right now), battery is full but energy price currently is such that discharging battery is not sensible so not using battery is fine. But why is not the solar power being used?! MPPT output is now 0W (panel array voltages are OK, but 0 amps drawn). Obviously battery can not be charged but Mupltiplus should still be able to use the MPPT for AC load (in other words pushing it out from AC IN)… Is it possible to control MPPT output via NodeRED? DESS logic is doing some strange things so I’d rather use our own DESS logic to maximise economic return of the system…
Just an update here. Apparently “sell energy to grid” option was disabled in ESS setup and this causes really strange behaviour. For some reason MultiPluss refuses to use DC sources (including solar) unless the sell energy to grid is enabled. MPPT is on “ext control” mode and operating well bellow the maximum set point. Once sell to grid option is enabled, it moves to maximum power point.
Logic here is really badly obfuscated. I wish in future Venus OS versions this would be improved. Also it seems that MPPT is impossible to set other than ext control mode if there is BMS connected. On the otherhand power point control does not seem to be possible via NodeRED. IMHO it should be to implement better logic to maximise harvested solar energy.
Thats isolated from ESS or DESS. Thats caused by DVCC. It essentially means that the internal charging algorithm of the MPPT is disabled, and the MPPT is controlled by DVCC, which in extension means its controlled by the BMS.
You cant force an MPPT to run on the max power point. The MPP is given by the crossing point of the PV voltage and current. The only way to get it to run on the MPP is to actually use the power that it can generate at the MPP. If you dont use the power, then it cant operate at the MPP.
When using ESS, and feeding DC energy to grid is allowed, then the system raises the absorption voltage by 0.6V automatically in order to keep the MPPTs producing power, which then can be used by the inverters to feed back to grid.
Yes that is certainly true, but for some reason Venus thinks it is better not use the solar energy instead of for example use it for charging the battery or run full load from the panel. Once feed into the grid is enabled, then it is able to use MPPT for charging battery as well. It is not even necessarily BMS related problem because if BMS is not connected and smart shunt is the authoritative battery monitor, it does not change the thing one bit. Once you flip the switch to allow grid feed in then all changes.
All export enables is an overvoltage condition so the mppts can generate and export.
You can enable export and set a limit of 0, that has helped some systems.
Might be that some of your voltages are off.
How did you change between the shunt and BMS? Physically disconnected it and restarted everything?
You can’t hotswap between managed and unmanaged.
To eliminate issues, it is helpful to run on purely ESS and not DESS so that you can be sure if it’s a broader issue or a specific one.
That voltage settings mismatch was something I suspected, but for life of me I haven’t been able to trace what could be off. And yes I physically disconnected everything and restarted when adding shunt, but in testing I just tried to change between shunt and BMS as Battery Monitor. Have to do some debugging.