I observed weird charging behavior when the charger changes from Absorption mode to Float mode. My system:
- MultiPlus II GX 3 kW, configured as ESS, with 230V / 16A grid connection
- AC-coupled Solar (3 kW) at the MultiPlus AC output
- DC-coupled Solar (SmartSolar), 880 W
- Battery monitoring using SmartShunt
- DIY LiFePo4 battery, 50V, JK-BMS, 16 kWh
After the Bulk and Absorption charging stages, with plenty of Solar production, what I expect to happen when changing to Float mode:
- Charging stops, discharging continues if required by AC loads, until Float voltage reached
- Float voltage maintained with small charge/discharge currents
- Re-bulk starts when battery voltage drops below Vfloat - 0.8V
What really happens:
- Charging stops, and the MultiPlus starts to discharge the battery actively as fast as possible until Float voltage reached. Since plenty of Solar production is present, this increases the Grid feed-in even more.
- If the 16A grid limit is reached, the MultiPlus switches off the SmartSolar DC-coupled source to keep draining the battery as fast as possible
- When Float voltage is reached the expected behavior returns…
I have increased the Float voltage to be closer to the Absorption voltage, this decreases the effect (see figure), but does not remove it completely. Since Float is meant to keep the battery in “rest” state, I do not expect active discharging to happen, especially while this increases grid feed-in, without any required AC loads. Any thoughts?
