Axpert-family inverters are sold under many names, but they share the same logic. At any moment the inverter is in one operating mode, decided by the settings you chose and by what is available: sun, grid or generator, and battery. Knowing those modes makes the front display, and a lot of unexplained behaviour, much easier to understand.
The operating modes
| Mode | What it means |
|---|---|
| Standby | The inverter is on but not supplying the output, typically switched off by the front switch while the grid or solar charges the battery. |
| Line mode | The loads are supplied from the AC input (grid or generator). Solar and the AC input may also be charging the battery. |
| Battery mode | The loads are supplied by the inverter from the battery and solar, with no AC input in use. |
| Power saving | With very little load, the inverter output pauses to save its own consumption and checks the load periodically. Disabled on most installations. |
| Fault mode | A fault has stopped the output. The fault code says why; the cause has to be removed before the inverter restarts. |
Source priority decides line or battery
The output source priority setting is the key to understanding why the inverter is in line or battery mode:
- Utility first: the AC input supplies the loads whenever it is available; the battery takes over during an outage.
- Solar first: solar supplies the loads first; if it is not enough, the AC input fills the gap.
- Solar, battery, utility (often shown as SBU): solar and battery supply the loads; the inverter switches to the AC input only when the battery reaches the voltage set as the return point.
The charger priority is a separate setting: solar only, solar first, or solar and utility together. Many "why did it charge from the grid?" questions come from this setting, not from the output priority.
Warnings versus faults
A warning means something is outside the normal range while the inverter keeps running: low battery, overload approaching its limit, high temperature, fan problem. A fault means the inverter has stopped its output to protect itself or the installation. Codes vary slightly between models and firmware, so always check the meaning in the manual of your exact unit. The pattern matters more than one occurrence: an overload warning every evening at the same time is a load that needs moving.
What to watch day to day
- Mode changes over the day: how often it switches to the grid in SBU tells you whether the battery or the solar array is undersized.
- Battery voltage at the switch-over point: if it drops there every night, the return voltage may be set too high or the battery too small.
- Load percentage: sustained loads close to the rating shorten the life of any inverter.
- Inverter temperature: a hot installation location shows up here long before it causes faults.
Seeing it without standing in front of it
Axpert Monitor reads the inverter through its RS232 port and turns the mode, the warnings and the faults into plain words, next to the PV power, the load, the grid and the battery values at the same moment. On your Wi-Fi you see it live; in Home Assistant every value becomes a sensor; with the free Cloud you keep three years of history, so each mode change has its context. It is read-only: your priorities and charge settings stay exactly as you set them.