Since a few days I have my ESS running, 3x MPII 5000, 1x Smart solar, Cerbo GX, 15kWh battery JK BMS (CAN), 4 SMA AC PV inverters with 10kWp PV and external grid meter from home wizard. Overall the system is working during the morning the battery is charging via the excess solar power using the ESS at -30W grid setpoint and at night it is discharging trying to keep that same setpoint which all seem to be working fine. The system uses DVCC controlled CVL CCL DCL via de BMS. The smart solar is set to grid feed in when battery is charged
But when the battery is fully charged the grid goes to at least -2kW (on sunny days) and I see some strange behavior on the ESS. The battery is continuously changing from charging to discharging every few seconds. I do not expect that this would be normal behavior (could be wrong offcourse).
below is a picture made with home assistant to get bit more resolution.
Graph 1: current through battery (postive to negative)
Graph 2: CVL and actual voltage
Graph 3: the grid power of each phase.
Below is picture and from the red line I switched to charge only mode with keep batteries charged and the current goes to zero when battery is full which is expected behavior
Personally I don’t think it is unusual behaviour. I see a similar thing on Pylontech when they hit 100% charge.
What does a graph of CCL plotted look like? That would indicate if the fluctuating charge current is due to the BMS altering CCL at the frequency you mention.
I did some more testing with CVL in the BMS to 56V and charge limit in the console to 55.2V but no effect. And switched again between charger only and ESS ON:
CCL does not do that. Also see no reason why because as long as the voltage of the charger and the battery is the same there would be flowing no current anyway. In the end the ESS determines when to charge and when to discharge not the battery.
In the end the ESS determines when to charge and when to discharge not the battery
No the BMS should be in control of the battery. It tells the Cerbo and ESS the charge & discharge current and voltage. DVCC then ensures that the various Victron components operate in a way to obey these parameters.
This protects your battery. The BMS should adjust CCL and DCL based on factors such as battery temperature and SoC.
ESS doesn’t need to care about your specific battery chemistry or configuration, it just does what the BMS tells it to do with regards charging and discharging.
yes that is true but BMS is only there to protect the battery but not to determine when needs to be charged and discharged. I would only expect the CCL to go to zero when there is an issue (overcharge, temperature issue etc).
Question is for how long this 500W discharge situation is present…
Because I’ve saw on my system that even 1 minute may pass until the system recovers and balances the situation. Quite slow sometimes…
Hence this charge / discharge thing, because if “x” time passes in discharge, then “y” time must pass to charge back.
Yeah, I have this issue with a JK BMS and DC PV. Even on float voltage 53.6, the BMS is flipping between 16A charge and discharge. It doesn’t do it if turn off the DV PV or stop it feeding in excess DC. Also, the charge-discharge current seems to depend on how much the MPPT is generating. It is interesting when you look at the battery current from the Multi it seems to be sucking up all the current from the MPPT so I am not sure why the BMS is doing this.
