Outback Power Systems FLEXmax 80 Owners Manual - Manual (Page 99)

Applications
900-0009-01-00 Rev C 97
ABSORBING
This is the second stage of charging. It is a constant-voltage stage. Current varies as needed to
maintain the Absorbing voltage setting. However, it 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 Absorbing stage is the user-defined Absorb Time Limit. The ChgT timer is preset
to zero following the previous charge cycle. Once in Absorbing, ChgT will count until it reaches this
limit. (See pages 20, 44, and 48.) The charger will then exit Absorbing and enter the Float stage. The
charger will also also exit Absorbing if the Absorb End Amps setting is reached, regardless of the timer.
This resets the timer to zero. (See page 44.) This stage is temperature compensated. (See page 97.)
FLOAT
When the charger enters this stage, it reduces the charging voltage to prevent overcharging of the
batteries. The batteries are maintained at the Float set point. Floating is displayed on the screen.
This stage is not timed. The FLEXmax will continue to maintain Float as long as PV energy is available.
If the PV cannot supply enough power to maintain the Float set point, the FLEXmax will not
immediately initiate a new charge cycle. It will attempt to draw more PV energy and recharge the
battery until the Float voltage set point is reached. When this occurs, MPPT Float is displayed
(see page 22). This stage is temperature compensated. (See page 97.)
A new charge cycle can be initiated if the voltage falls below the ReBulk set point (see page 50).
Battery Temperature Compensation
Battery performance changes when the temperature varies above or below room temperature (77°F
or 25°C). Temperature compensation is a process that adjusts charging to correct for these changes.
When a battery is cooler than room temperature, its internal resistance goes up and the voltage
changes more quickly. This makes it easier for the charger to reach its voltage set points. However,
while accomplishing this process, it will not deliver all the current that the battery requires. As a result,
the battery will tend to be undercharged.
Conversely, when a battery is warmer than room temperature, its internal resistance goes down and
the voltage changes more slowly. This makes it harder for the charger to reach its voltage set points.
It will continue to deliver energy as time passes until the charging set points are reached. However,
this tends to be far more than the battery requires, meaning it will tend to be overcharged.
The FLEXmax controller, when equipped with the Remote Temperature Sensor (RTS) will compensate
for temperature. The RTS is attached to a single battery near the center of the bank. When charging,
the RTS will increase or decrease the charge voltage by 5 mV per degree Celsius per battery cell. This
setting affects the Absorbing and Float set points. Equalization is not compensated in the FLEXmax.
 In a 12 Vdc system (6 cells, 2 volts each), this means 0.03 volts per degree Celsius above or below 25°C.
Maximum compensation is ± 0.6 Vdc.
 In a 24 Vdc system (12 cells, 2 volts each), this means 0.06 volts per degree Celsius above or below 25°C.
Maximum compensation is ± 1.2 Vdc.
 In a 48 Vdc system (24 cells, 2 volts each), this means 0.12 volts per degree Celsius above or below 25°C.
Maximum compensation is ± 2.4 Vdc.
Examples:
 A 12 Vdc system with 10°C batteries will compensate its charging to 0.45 Vdc higher than the set points.
 A 24 Vdc system with 35°C batteries will compensate its charging to 0.6 Vdc lower than the set points.
 A 48 Vdc system with 15°C batteries will compensate its charging to 1.2 Vdc higher than the set points.