Samlex America SCC-30AB - Manuel (Page 32)

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4
PRINCIPLE OF OPERATION & FEATuREs
Stage as explained above under heading “Automatic Equalization After 28 Days.”
Termination of Equalization Stage in Manual Mode Before Completion: If the unit
is set for manual Start / Stop of Equalization Stage (Using DIP Switch No. 5) and
equalization is switched ON but is switched OFF before completion, the charger
reverts to “Bulk Stage” and undergoes Normal Charging Algorithm explained above.
Temperature Compensation During Charging
The temperature of the battery electrolyte affects the rate of chemical reactions in
the batteries as well as the rate of diffusion and the resistivity of the electrolyte.
Therefore, the charging characteristics of the battery will vary with temperature. This
is nearly linear and the Voltage Coefficient of Temperature Change is normally taken
as -3 mV to -5 mV / ºC / Cell. Please note that the Voltage Coefficient of Temperature
Change is negative which means that as the temperature rises, the charging voltage is
required to be reduced and as the temperature is decreased, the charging voltage has
to be increased.
All charging voltage set points are normally specified at 25ºC / 77ºF. In PV systems,
battery temperatures often vary up to 15ºC from the 25ºC reference. The Absorption,
Float & Equalization Voltages must then be adjusted, or a controller with Temperature
Sensor should be used. Table below shows example of adjustments for Absorption
Voltage of say 14.4V for 12V battery (based on Voltage Coefficient of Temperature
Change as -5 mV / ºC / Cell or -30mV (.03V) for a 6 cell, 12V battery):
Battery Temperature Absorption Voltage
40ºC 13.95V
25ºC (Reference) 14.4V (Reference)
10ºC 14.85V
In case temperature compensation is not provided, the warmer battery at 40ºC will
begin to heat and outgas at 13.95V and will continue to overcharge until the non-
compensated Absorption Voltage set point is reached (14.4V). In cooler temperatures,
the 10ºC battery will experience severe undercharging resulting in sulfation.
The controller has provision for temperature compensation with the help of optional
Temperature Sensor Model DC-BTS-A-C. This Temperature Sensor is required to be
connected to the terminals marked BTS+ and BTS- (Fig 5.2).
It is recommended that the above optional Temperature Sensor may be used if the
battery electrolyte temperature varies more than 5ºC to 10ºC (9ºF to 18ºF) from the
reference temperature of 25ºC (77ºF).
For more details on installation of the above Temperature Sensor, please read under heading
“Temperature Compensated Battery Charging” on page 45.