46
Selectronic Australia
Rev 41 - Dec 2022
Operation
Battery Voltage Monitoring and Control
The SP PRO measures the battery voltage both at the inverter and at the battery terminals (when the Battery
Sense / pre-charge wiring is installed). Sensing the battery terminal voltage (using Battery Sense / pre-charge
wiring) compensates for the effect of Cable Losses which, irrespective of charge or discharge currents, keeps
the battery terminal voltage within set limits.
In a managed battery, the Battery Sense voltage is read directly from the battery BMS via the SP PRO CAN
bus interface. This means the Battery Sense / pre-charge wiring is only used for pre-charge.
Battery voltage is used to protect the system by shutting charging sources (should the battery voltage go
above set limits) or shutting down the inverter (should the voltage drop too low). For the low voltage shutdown
limits the SP PRO employs different levels depending on system Load.
The system will always attempt to reconnect to the grid or start the backup generator (when installed) before
shutting the inverter down due to low battery voltage or low SoC.
Battery Charging Operation
The SP PRO charging system manages all charging sources in the power system giving priority as appropriate
to the renewable energy sources. This ensures that the renewable sources are used in the most cost-effective
manner.
The SP PRO continuously monitors all charging sources to recharge the battery in a five-stage cycle. Each
stage or charging mode is controlled by voltage, current and time settings. These settings are fully
configurable using SP LINK and should not require changing after initial installation, unless some aspect of the
battery installation changes.
Each voltage setting is battery-temperature compensated. The set values displayed do not change.
For details see
Battery Temperature Compensation
on page 48.
Battery Charging Mode
Read the following with reference to the battery charging cycle graph on the following page.
Initial
The SP PRO charges at the Initial charging current until the battery voltage rises to the Initial charge voltage,
then holds this voltage for a set time before starting the Bulk stage. When in the Initial charge phase, the Initial
/ Bulk indicator will flash.
Bulk
The SP PRO charges at the Bulk charging current until the battery voltage rises to the Bulk charge voltage,
then holds this voltage for a set length of time before starting the Absorption stage. In Bulk charge mode, the
Initial / Bulk indicator will be steady ON.
Absorb
In the Absorption charge phase, the SP PRO will charge at the Absorb charge current until the Absorb charge
voltage is reached. Once this voltage is reached, the SP PRO will carefully monitor the rate of change of the
charge current as set in the Absorb-Float transition setting.
When the Absorb-Float transition setting is met, the charge cycle will switch to Float and terminate an auto
start backup generator if connected. If an Equalise charge is pending, the Equalise charge cycle will now be
performed. The Absorption indicator will be steady ON when in the Absorption phase.
Float
The SP PRO holds the battery voltage at the Float level and will provide up to the Float current to maintain the
Float voltage. The SP PRO will remain in this charge state until battery falls below the Initial Return voltage or
Initial Return SoC settings. If the SP PRO is still connected to an AC Source after 24 hours of Float, the charger
will transition to the long-term Float voltage. Long-term Float voltage will allow batteries to sit at a lower
voltage level indefinitely, reducing battery losses.
Equalise
Where a periodic Equalise is required by the installed battery type, the SP PRO will periodically hold the
battery at a higher voltage for a set period. This will help all cells within the battery bank have an equal
amount of charge. The Equalise indicator will be steady ON when in Equalise mode and will flash when an
Equalise is pending. That is, the charger will perform an Equalise after Float stage is next reached.
Battery Charging:
Lead acid batteries (such as gel, flooded, AGM, VRLA) normally start to take less
charge when they reach 80% state of charge (SoC) and above. It is normal to see the charge current
reducing and PV controllers (including Managed AC Coupled solar) power limiting when the
batteries reach 80% SoC.
SP PRO Operation
