Since a couple of days, my ESS is finally up and running.
My setup:
3x Multiplus II 48/5000
Cerbo GX
SolarEdge SE10k
Victron 1000a ip65 Smartshunt connect to VE.direct
16kWh Yixiang DIY battery with the JK BMS connected to the Cerbo (BMScan)
RCV: 55.20V
CCL: 95A
DCL: 95A
I’m noticing some strange behavior when the battery is almost full—or at least I think it’s strange…
I’ve attached a video to clarify what I’m experiencing. When the battery is almost full, the system rapidly switches from charging to discharging, even though this shouldn’t be necessary as there is an excess of PV available. I’ve already tried troubleshooting everything I could think of and double-checked all settings.
Could anyone help me out and maybe point me in the right direction, assuming this is not normal behavior?
The JK BMS is not able to recognize current below 2 Amps correctly … so it if it is below that value, it communicates rubbish on small current changes. The reason for this is the missing shunt (current is measured on one of 20 tiny resistors) which makes it very inacurate in currents.
conclusion: you system is working as normal as possible with this kind of BMS.
It could also be the BMS balancing the battery cells. Most BMS use passive cell balancing, that means, it cannot transfer energy between cells, it can only “reduce” the current a single cell is receiving compared to others during charging.
That means, whenever one cell hits it’s critical voltage, while the cells are not yet balanced, the BMS has to discharge all cells a bit, then charge them again while throttling the highest voltage cell - until it hits it’s critical voltage again.
Depending on the balancing state, that can repeat over several hours.
Lot of BMS also won’t show 100% SoC, until the cells are balanced.
That sounds like a very plausible explanation—thanks a lot for your insight!
Would you suggest any changes to this setup? I forgot to mention that I also have a SmartShunt connected to the system via VE.Direct. However, it’s not performing very well, at least with the current settings I’ve applied.
When using the SmartShunt as the battery monitor, I’m seeing very unstable load voltages going into the battery, which I haven’t been able to stabilize. It also doesn’t seem to respect the CVL settings configured in DVCC.
Do you think it’s possible to use the SmartShunt as the battery monitor while letting the JK BMS handle the parameters like CVL, CCL, and DCL?
