Samlex-america SCC-30AB Bedienungsanleitung PDF herunterladen (Seite 15)

GENERAL INFORMATION: BATTERIEs

Effect of Temperature on Battery Voltage

The temperature of the 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 Coefcient of Temperature Change is normally taken

as -3 mV to -5 mV / ºC / Cell. Please note that the Voltage Coefcient of Temperature

Change is negative. This 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 specied at 25ºC / 77ºF. In solar

systems, battery temperatures often vary up to 15ºC from the 25ºC reference. The

Absorption, Float and 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 Coefcient of

Temperature Change as -5 mV / ºC / Cell or -30mV (.03V) for a 6 cell, 12V battery).

BATTERY TEMPERATURE ABSORPTION VOLTAGE (12V BATTERY)

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.

It is recommended that a battery charger / charge controller with a provision for

temperature sensing and compensation should be used if the battery electrolyte

temperature varies more than 5ºC to 10ºC (9ºF to 18ºF).

Self-discharge

The battery discharges itself even without any load connected to it. This effect is

caused by secondary reactions at its electrodes and proceeds faster with higher

temperature or in older batteries. Thermodynamic instability of the active materials

and electrolytes as well as internal and external short-circuits lead to capacity losses,

which are dened as self-discharge. This loss should be small, particularly in respect of

annual storage. Self discharge (% of loss of capacity per month) for various types of

batteries is as follows:

• Lead Acid 3% to 4%

• Ni-Cd 6% to 20%

• Ni-Fe 40%

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Samlex-america SCC-30AB Bedienungsanleitung Seite 15