Outback Power Systems FLEXmax 80 Owners Manual - Manual (Page 98)

Applications
96 900-0009-01-00 Rev C
Three-Stage Battery Charging
The FLEXmax charge controller is a sophisticated, multi-stage battery charger that uses several
regulation stages to allow fast recharging of the battery system while ensuring a long battery life. This
process can be used with both sealed and non-sealed batteries. The FLEXmax is a “buck” converter
which turns higher PV voltages into the lower charging voltages used by batteries (with
correspondingly higher currents). The chart in Figure 100 shows the voltage levels achieved by the PV
array throughout a typical day, and the battery voltages (by stage) during the same times.
The FLEXmax has preset recharging voltage set points (Absorbing and Float voltages); however,
OutBack always recommends using the battery manufacturer’s recommended charging voltages.
Figure 100 FLEXmax 80 Three-stage Battery Charging
A new charge cycle is started any time the battery voltage decreases below the Rebulk set point .
(See page 50.) This usually occurs each night unless the batteries were maintained by another means.
(If so, they may not need to be recharged). See pages 20 through 24 for the messages displayed
onscreen during the various stages.
BULK
This is the first stage in the three-stage charge cycle. It is a constant-current stage which drives the
battery voltage up. The DC current is the maximum current the charger can deliver. This stage
typically leaves the batteries at 75% to 90% of their capacity, depending on conditions.
In the Bulk stage, the FLEXmax will charge the batteries to the Absorbing voltage setting (see
page 26). This stage is not timed. It will charge as long as necessary to complete the stage, regardless
of any timer set points. If little PV energy is available, it may take a long time for this stage to
complete. If the FLEXmax is in a different charging stage and little PV energy is available, it may return
to Bulk. (See page 20.) This stage is temperature-compensated. (See page 97.)
Inp
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Time