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Prosine 2.5/3.0 Installation & Operation Guide 59
Section 6: Multistage Charging
The Prosine inverter/charger has a fully functional multistage battery charger. Any time an acceptable
(within frequency and voltage parameters) AC source is presented to the unit, it will charge the
batteries connected to it. When AC is present and the charger is enabled, the charger will charge the
battery bank regardless of the position of the inverter’s On/Off switch.
Charging Profile
The battery charger in the Prosine charges in three stages—BULK, ABSORPTION, and FLOAT—
to provide rapid and complete charge cycles without undue battery gassing. The figure below shows
how DC voltage and current change with time through the different charge stages.
Figure 7. Three-Stage Charging Profile
Bulk Charge
In the first step, known as the bulk charge, the Prosine inverter/charger delivers the maximum charge
current allowable given the configuration settings, that is, battery type and temperature, maximum AC
input setting and battery bank size. This current is delivered to the batteries until the battery voltage
approaches its gassing voltage—typically around 14.4 volts for 12 volt batteries and 28.8 volts for 24
volt batteries (again this voltage can vary depending on battery type and other settings). The bulk
charge step restores about 75% of the battery's charge. The gassing voltage is the voltage at which the
electrolyte in the battery begins to break down into hydrogen and oxygen gases. Under normal
circumstances, a battery should not be charged at a voltage above its gassing voltage since this will
cause the battery to lose electrolyte and dry out over time. Therefore the Prosine inverter/charger
transfers to the next stage, known as the absorption charge.
Absorption Charge
During the absorption charge, the charging voltage is held constant near the gassing voltage and the
charging current is steadily decreased. When the charging current has decreased to a predetermined
Bulk
Absorption Charge
Float Charge
DC Voltage
DC Current
Constant Current
@ Maximum
Charge Rate
Constant Voltage
Reduced Current and Voltage
Bulk Volts Setting
Float Volts Setting
Time
Charging
Started
Reduced Voltage
Load current on demand