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56 Freedom SW 3000 Owner’s Guide
Battery Charging Reference
Charge Algorithm Stages
Three-Stage charging
If three-stage charging is enabled, the Freedom SW 3000 will charge
batteries in a sequence known as three-stage charging. The charging voltage
delivered to the battery depends on the battery:
• type setting
• temperature (by switch setting or battery temperature sensor)
• state of charge
The three automatic stages are:
• bulk
• absorption
•float
See Figure 27 for a graph of the three-stage charging profile.
There is a fourth stage, equalization, which is initialized manually as it is
only performed occasionally and only on flooded (or wet) batteries.
Bulk Charge In the first stage—the bulk charge—Freedom SW 3000
delivers its full-rated output current. This constant current is delivered to
the batteries until the battery voltage approaches its gassing voltage—
typically around 13.5 volts for 12 volt batteries. The bulk charge stage
restores about 75% of the battery’s charge.
The exit from bulk stage to the next stage, absorption, occurs under the
following condition:
• battery voltage is more than the gassing voltage (V
G
) for a specified
amount of time (3 minute default).
With an AC reconnect to qualified AC from the utility power or a generator
during the bulk stage, the unit will return to the bulk stage.
Absorption Charge During the first part of absorption charge, the
Freedom SW 3000 delivers its full rated output current until the absorption
voltage is reached. At this point, the Freedom SW 3000 will transition to a
constant voltage mode by keeping the charge voltage constant at the
absorption voltage level, and the battery gradually reduces the charging
current it demands as the battery attains full charge.
The absorption stage has the following exit criteria:
• Overall time in absorption timeout (ΔT
A
) has a default of 6 hours.
• Time in constant voltage absorption timeout (ΔT
CV
)
has a default of 1
hour.
• Charge current level drops below a specified limit (I
H
) for a specified
amount of time, which has a default of 2% of C in Ah for 3 minutes.
See “Charge Algorithm Definitions” on page 58 for more information.
With an AC reconnect during the absorption stage, the unit will transition to
the float stage for three-stage charging and no-float stage for two-stage
charging.
Float Charge In the third stage—the float charge—which is a
maintenance mode, the output voltage of the charger is reduced to a lower
level, typically about 13.5 (V
F1
) volts to maintain the battery’s charge
without losing electrolyte through gassing.
With AC reconnected during this stage, the unit will return to the float
stage.