ESS takes power from the grid instead of the battery

In the “Charger only” position, the inverter/charger does not discharge the battery. You cannot see the switch status in VRM or on the GX device — you have to check it on site. On the MultiPlus-II, the switch is on the bottom of the unit and must be in position I, not II.

When mains is available, ESS stops discharging the battery when SoC falls to the Minimum SoC set in the ESS menu. Example from the manual: at 60%, the 60–100% range is used for self-consumption, and 0–60% — for a mains failure. When mains fails, in inverter mode, the battery keeps discharging until other thresholds operate.

• BatteryLife (code #2) can raise this limit every day — in poor sunlight by 5% per day, until the energy taken from the battery over 24 hours matches the energy replenished. As solar input increases, the limit returns to the set value day by day.
• Discharge is allowed again when SoC rises by at least 3% above the set limit.
• The limit also works according to battery voltage (Dynamic cut-off) and BMS signals — not only according to SoC.

This applies to batteries with CAN-bus communication. On the GX device, open the battery in the device list, then the Parameters submenu, and check Discharge Current Limit (DCL). A value of zero means the battery does not allow the system to discharge it further (in the GX overview — code #4).

Before the inverter/charger in an ESS system starts using the battery, it must perform a relay test — for about a minute it then operates as an inverter and needs stored energy in the battery for this. If the battery voltage is too low when connecting to mains, the system starts in passthru or charging mode and waits for the battery to be charged. Until then, it does not convert direct current to alternating current: it does not power loads from the battery, does not pass energy from MPPT solar charge controllers to them, and does not export surplus from the panels to mains.

The test will run when battery voltage exceeds 14 V, 28 V or 56 V (for 12, 24 and 48 V systems) or when SoC exceeds 20%. You can check the status on the GX device: device list → Multi/Quattro → Advanced submenu → ESS Relay test — “Pending” or “Completed”. This item is visible only in systems with the ESS assistant.

Some grid codes (for example German or Australian) use the AUX1 input to disable export. If AUX1 is connected to something else — for example an AC sensor or BMS — it may block system operation in this way. The manual’s solution: untick this option in the grid code settings (VEConfigure). The manual also lists grid codes that require discharge permission via the AUX inputs — compare the set code with the signals actually applied to the unit’s AUX inputs.

According to the ESS manual, the system enters passthru mode when:

• the GX device has stopped receiving data from the grid meter — this applies to systems configured with an external meter (Settings → ESS → Control without grid-meter); see also error GX #49;
• in a system with a lithium battery on CAN-bus, the GX device has stopped receiving information from the battery;
• charging is not allowed (maximum charge current from the BMS = 0 A or maximum charge power = 0 W), and there is surplus energy from the panels;
• discharging is not allowed (BMS: DCL = 0 or SoC below Minimum SoC), and the loads on the AC output require more than the input current limit allows;
• the grid code requires discharge permission via the AUX inputs (step 5);
• loss of mains detection (LOM) is causing problems — often with a supply that has high impedance (step 7).

The manual points to Loss of Mains (LOM) detection, linked to the country code set in VEConfigure. This happens when the AC input supply is “weak”, meaning the connection to mains has higher impedance than usual — for example a generator, or an old or remote house connected by a long or too-thin cable. The Victron document “VEConfigure: grid codes & loss of mains detection” describes the solutions and configuration options. If none of the steps helps, the manual advises temporarily disabling LOM to rule out this cause.

In Optimized mode, ESS charges the battery from mains only in situations that protect it from damage:

• Sustain — switches on only after the battery is considered discharged (voltage below Dynamic cut-off or a low cell voltage signal from the VE.Bus BMS). The system then maintains the Sustain voltage — in a 12 V system: 12.5 V for lithium batteries, and for others 11.5 V for the first 24 hours, then 12.5 V — charging from mains at a maximum of 5 A per device (regardless of system voltage). The mode ends when the panels raise the voltage by 0.1 V above the Sustain level (0.2 V at 24 V, 0.4 V at 48 V).
• BatteryLife slow charge (code #5).
• Auto-recharge — when SoC falls by 5% or more below Minimum SoC, the system charges the battery from mains up to the Minimum SoC level.

What the manual says to do: increase Minimum SoC, for example by 5%, and observe what happens. You can also lower the Sustain voltages in VEConfigure, but be careful — especially with lead-acid batteries, because the Sustain levels protect them from premature damage.

The sequence from the “Troubleshooting” chapter:

• check the “#” status codes in the GX overview;
• check the cabling — a large voltage drop between the MPPT solar charge controller and the inverter/charger prevents effective supply of AC loads from the panels;
• check operation with SVS (shared voltage sense) enabled and disabled — leave it disabled;
• check the MPPT solar charge controller charge current limit (CCL) when the panels are only lightly loaded — it should always be high, even with a full battery, unless temperature is limiting it;
• check the MPPT charge voltage setpoint (Charge Voltage Setpoint) — it should be higher than the current battery voltage. The software calculates both of these last parameters from values sent by the lithium battery over the CAN-bus; you cannot set them manually, but they help you understand what is happening.

In Keep batteries charged mode, when the battery is full, the MPPT solar charge controller may produce less — when DVCC is disabled and “Feed-in excess solar charger power” is disabled. Workarounds from the manual: enable DVCC (if the GX device manual for that battery allows it) or set Optimized mode with Minimum SoC 100% — but then, if mains fails, the system will not charge the battery from mains.

• Feed-in excess solar charger power — for panels connected through MPPT controllers (DC), this setting must be On. The controller then always runs at full power: it first supplies the loads, then charges the battery, and sends the rest to the grid. Manual note: the DVCC charge current limit then stops working — with a small battery, set a safe limit in the controllers themselves.
• Grid feed-in — in this menu you can completely disable or limit feeding energy from AC and DC solar panels back to the grid. Feed-in only happens when the surplus fully covers the loads and the battery is charged (or charging at the maximum permitted current). The “Feed-in limiting active” indicator shows “Yes” only when the limit is currently active.
• Feed-in is also blocked by an unfinished relay test (step 4) and by the grid code using the AUX1 input (step 5).