Instruction Manual

Charge Controlling
975-0400-01-01 Revision H 1–5
This manual is for use by qualified personnel only.
Three-Stage Battery Charging
The three-stage charging process results in more efficient charging compared to
on-off relay type or constant voltage solid-state regulators. The final float stage
reduces battery gassing, minimizes electrolyte loss, and ensures complete
battery recharging. Battery voltage and current vary during the three-stage
charging process as shown in Figure 1-4.
Bulk Stage
During the bulk stage, the solar charge controller operates in constant current
mode, delivering maximum current to the batteries. When the battery voltage
reaches the Absorption voltage setting, the controller automatically transitions to
the absorption stage.
Absorption Stage
During the absorption stage, the solar charge controller operates in Constant
Voltage mode and the current falls gradually as charge is returned to the battery.
The voltage limit used for the first 60 minutes of this stage is the Bulk Voltage
setting. The voltage limit used for the remaining time in this stage is the
Absorption Voltage setting.
By default, the charge controller uses the same Bulk and Absorption voltage
setting for all battery types. The default voltage limit settings (Bulk and
Absorption) can be adjusted if the battery type is set to Custom. For flooded lead
acid batteries only, a custom charging scheme can be used which sets the Bulk
voltage higher than the Absorption voltage. The result of this is a boost voltage
charge level, which has been found to be beneficial for ensuring effective
charging of the battery bank for off-grid installations.
For detailed information on how Boost charging works and when it is
recommended, please refer to Appendix C, “Boost Charging”. The solar charge
controller transitions to the float stage if either one of two conditions are met:
1. The charge current allowed by the batteries falls below the exit current
threshold, which is equal to 2% of the programmed battery capacity (for a
500 amp-hour battery bank, this would be 10 amps), for one minute.
2. The solar charge controller has been in absorption for the programmed
maximum absorption time limit. The default is 3 hours, but the time limit is
programmable from 1 minute to 8 hours.
Float Stage
During the float stage, the voltage of the battery is held at the float voltage
setting. Full current can be provided to the loads connected to the battery during
the float stage from the PV array. When battery voltage drops below the
ReCharge Volts setting for 1 minute, a new bulk cycle will be triggered.