elvisfox

According to the manual, there should be one with PV charging current but it is not present in practice. Probably it appears if the solar is connected (because I only use it as UPS without PV), but I am not sure. When operating from the mains there is no screen that would report a charging current.

Hi @Coulomb, So I did some testing yesterday. I have discharged my batteries to nearly 0% SOC on purpose (but before UV shutdown), and then switched on the grid. After that it actually went to CV (28.4V in my case), and it stayed there for about 6 hours before I stopped it manually. The charging current actually dropped below 0.2A after 15 minutes of CV (monitored through BMS), but it did not trigger the inverter back to float. Remarkably, the fan was constantly blowing at full speed even with no battery current. So, no, it is not terminated by the charge current, it actually does that 10*T1. Also my inverter does not report charging current through LCD. Battery current is only displayed while discharging, but when charging from grid it reports 0. So I am not sure if it is even capable of monitoring the charging current. I suspect the feedback is in hardware, not in the firmware, so it keeps CV for 10*T1 whatever the current is.

I have the same issue with MasterPower Omega, which is another Axpert VM 3000 clone (the MPPT version of first-generation V solar inverters). It is related to the way how they calculate absorption time. If the battery does not fall below 24.8 V during discharge, the firmware assumes there is no need to absorb, thus it goes directly to float. If you discharge low enough, it will measure the charging time up to 24.8V and use that to calculate the absorption time (10 * T1), where T1 is the charge time until reaching 24.8V. This is annoying when using it with LiFePO4 batteries, but I think that's the price we pay when buying the cheapest inverters on the market.