Outback FM60 User Manual

Applications
98 900-0009-01-00 Rev D
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 53.) This usually occurs each night unless the batteries were maintained by
another means. (If so, they may not need to be recharged). See pages 22 through 26 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 29). 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 stage and little PV energy is available, it may
return to Bulk. (See page 22.) This stage is temperature-compensated. (See page 99.)
Time