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Charge Controlling
975-0400-01-01
1–5
Absorption Stage
During the absorption stage, the XW SCC continues to deliver its maximum
available current output until the battery voltage reaches the absorption voltage
setting. The XW SCC then operates in constant voltage mode, holding the battery
voltage at the absorption voltage setting for a pre-set time limit (the default time
limit is three hours). During this time, current falls gradually as the battery
capacity is reached. The XW SCC transitions to the float stage if any one of three
criteria are met:
1. The charge current allowed by the batteries falls below the exit current
threshold, which is equal to 2% of battery capacity (for a 500 amp-hour
battery bank, this would be 10 amps), for one minute.
2. The battery voltage has been at or above the float voltage (which it reached
during the bulk stage) for eight hours.
3. The battery voltage has been at the bulk/absorption voltage setting for a pre-
set time limit (the Max Absorb Time).
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.
Figure 1-4
Three-stage Battery Charging Cycle
a
a.An actual charging cycle for a PV-based system that is in use while it is being charged will
likely differ from the cycle represented in Figure 1-4. This is because a PV system’s output
is limited by the amount of solar energy available, and also because DC loads will affect the
charge current and the measured battery voltage.
Time
Float Stage
Absorption Stage
Bulk Stage
Absorption—
constant current
Absorption—
constant voltage
Current
Voltage
Time
Bulk/Absorption Voltage
Float Voltage Threshold
ReCharge Voltage Threshold
Exit Current Threshold
Max Absorb Time—3 hours
(adjustable 2–6 hours)
Max Current Limit
Maximum 8 hours (fixed)
Float voltage
Bulk Stage
Absorption Stage
Float Stage
Summary of Contents for XW-MPPT60-150
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