Alpha Group OutBack Power FLEXmax Extreme Series, Owner'S Manual

Page: 73 / 84

Applications
900-0150-01-00 Rev A
71
Three-Stage Battery Charging
The FLEXmax Extreme 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 Extreme 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 63 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 63 FLEXmax Extreme Three-stage Battery Charging
A new charge cycle is started any time the battery voltage decreases below the
Rebulk
set point for 90 seconds
or more. (See page 36.) This usually occurs each night unless the batteries were maintained by another means.
(If so, they may not need to be recharged).
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 Bulk, the controller will charge the batteries to the Absorbing voltage setting (see page 36) . This stage is not
timed. It will charge as long as necessary, regardless of any timer set points. If little PV energy is available, it may
take a long time for Bulk to complete. If the FLEXmax is in a different charging stage and little PV energy is
available, it may return to Bulk. (See page 25.) This stage is temperature-compensated. (See page 72.)
Absorption
This is the second stage of charging. It is a constant-voltage stage. Current varies as needed to maintain the
Absorbing voltage setting, but will typically decrease to a very low number over time. This “tops off the tank”,
leaving the batteries at essentially 100% of capacity.
The duration of the Absorption stage is the user-defined Absorb Time Limit . Once in Absorbing, the internal
counter will count until it reaches this limit. (See page 26.) The controller will then exit Absorbing and enter the