2020-12-11 00:44
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Hub-4 / grid parallel - manual DEPRECATED
Victron Energy - https://www.victronenergy.com/live/
6. Battery charging and discharging behavior
(Note: All absolute voltages mentioned in the text below are for a 12V system and should be
multiplied by 2 or 4 for a 24V or 48V system.)
When there is less PV power available than needed by the loads (a PV shortage), energy stored
in the battery will be used to power the loads until the battery is considered empty. There are
three parameters that check if the Battery is empty:
Battery State of Charge. Minimum state of charge is configured in the Hub-4 Assistant.
1.
Battery Voltage. See Dynamic Cut-off section below.
2.
Low cell signal from BMS
3.
When the battery is empty, the Sustain mode is activated. See Sustain section below.
Whenever there is excess PV, the battery will be charged. Charge current and other parameters
are configured on the Charger tab in VEConfigure3.
The Hub-4 Assistant will disable PowerAssist. Please keep this option disabled.
Make sure to keep the lithium batteries checkbox on the charger page consistent with the
battery choice in the Assistant.
Sustain Mode
The purpose of the Sustain Mode is to prevent battery damage caused by leaving batteries in a
deeply discharged state. The Sustain Mode is entered as soon as the battery is discharged, see
above.
During Sustain Mode, the batteries will slowly be charged from the grid; maximum charge current is 5
Ampére. The Sustain level is 12.5V for lithium batteries. For non-lithium batteries, the sustain level is
11.5 V for the first 24 hours, and after that it is raised to 12.5 V.
Excess solar power will also be used to charge the batteries. Sustain stops as soon as there has been
sufficient excess solar power available to raise the battery voltage 0.1 V above the sustain level.
Normal operation will then continue: solar deficits are complemented with power from the battery
again.
Dynamic Cut-off
Note: dynamic cut-off is useful for batteries with a high internal resistance. For example OPzV and
OPzS. Less relevant for LiFePO4 batteries, see graph.
With Dynamic Cut-off, the dc-low-disconnect level is a function of the battery current drawn from the
battery. When a high current is being drawn from the battery, a lower DC cut-off voltage threshold is
being used, for example 10 V. And similarly, when the battery is only being discharged slowly, a high
DC cut-off voltage is used, for example 11.5 V.
This way, voltage drop caused by battery internal resistance is being compensated for, and battery
voltage can reliably be used to stop discharging when the battery is discharged.
The picture below shows the default 'Discharge' vs. 'DC input low shut-down voltage' curve for the
different battery types. The curve can be adjusted in the assistant.
