Xantrex Technology 815-2012, 815-3024 Absorption Stage, Float Stage, Battery Charging Reference

Freedom SW 3K2K InvChg Owners Guide.book Page 60 Wednesday, October 9, 2013 1:34 PM

Battery Charging Reference

Absorption Stage

During the absorption stage, the Freedom SW begins operating in constant voltage mode and the current falls gradually as the amp hours are returned to the battery. By default, the bulk and absorption voltage settings are the same for all battery types. The voltage limit settings for bulk and absorption can be adjusted independently if the battery type is set to Custom.

Once the Freedom SW reaches the Bulk (Absorption, after the first 60 minutes) Voltage setting, the Freedom SW will operate in constant voltage mode, providing only the necessary current to maintain the voltage setting. As the amp hours are returned to the battery, the current required to maintain the voltage setting falls gradually.

The Freedom SW transitions to the float stage if either one of the following 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 three minutes.

2.The Freedom SW 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.

NOTE: If there are DC loads on the batteries, the charger’s current may never decrease to a level to initiate the next stage of charging. In this case, the charger would stay in absorption until the Absorb Time setting is reached.

NOTE: To make sure the charger does not remain in absorption for too long, adjust Absorb Time on the Charger Settings menu. The timer begins at the start of the absorption stage and terminates absorption charging if the charge current does not decrease to below 2 per cent of the battery capacity before the Absorb Time setting expires. The Absorb Time setting may be increased if the charge cycle continually runs the full Absorb Time in the absence of DC loads. This is an indication of too large a battery bank for the selected Absorb Time setting.

Float Stage

Float charge maintains the batteries slightly above the self discharge voltage of the batteries. The charge current in float is the current necessary to maintain the batteries at the Float Voltage setting, limited only by the inverter's capability or other settings that limit the inverter's maximum charge rate. Float charging reduces battery gassing, minimizes watering requirements (for flooded batteries), and makes sure the batteries are in a constant state of readiness. When three-stage charging is selected, the charger automatically switches to the float stage after the batteries have received a bulk and absorption charge (see Figure 32). The batteries are maintained at the default float voltage level for the selected battery type or the voltage selected under Float Voltage on the Custom Battery Settings menu.

NOTE: The battery voltage can increase above the float voltage when using an external charging device such as PV arrays, wind turbines, and micro-hydro generators. Be sure to include appropriate charge management equipment with all external DC sources.

60 Freedom SW Owner’s Guide