Product Manual

Operation
900-0167-01-00 Rev B 37
Battery Temperature Compensation
Battery performance will change when the temperature varies above or below room temperature
(77°F or 25°C). Temperature compensation is a process that adjusts battery 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 FXR inverter, when equipped with the Remote Temperature Sensor (RTS) will compensate for
changes in temperature. The RTS is attached to a single battery near the center of the bank, to achieve
a representative temperature. The FXR inverter has a designated port for installing the RTS.
If installed in a multiple-inverter system, only a single RTS is necessary. It must be plugged into the
master inverter and will automatically control the charging of all slaves and all charge controllers.
When charging, an inverter system with an RTS will adjust the charging voltage inversely with changes
in temperature. It will
increase
the charge voltage by 5 mV for every decrease of 1 degree Celsius per
battery cell. Similarly, it will
decrease
the voltage 5 mV for every increase of 1°C per cell.
This setting affects the
Absorption
,
Float
, and
Equalization
set points. The
Sell Voltage
and
Re-Float
Voltage
set points are not temperature compensated. The
Equalization
set points are not
compensated in OutBack charge controllers.

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 batteries at 10°C will compensate its charging to 0.45 Vdc
higher
than the set points.

A 24 Vdc system with batteries at 35°C will compensate its charging to 0.6 Vdc
lower
than the set points.

A 48 Vdc system with batteries at 15°C will compensate its charging to 1.2 Vdc
higher
than the set points.

A 48 Vdc system with batteries at 40°C will compensate its charging to 1.8 Vdc
lower
than the set points.
Slope
Some batteries require different amounts of compensation. The OutBack FLEXmax Extreme charge
controller has an adjustable rate of compensation (“slope”) and is not limited to 5 mV. The FLEXmax
Extreme can be networked with the inverter with the HUB Communications Manager. If this is done,
the inverter can import the slope setting from the FLEXmax Extreme charge controller.
NOTE
:
Temperature compensation only applies to the battery charging function. Other set points in the
inverter, such as the AUX functions, are not compensated for temperature.