Alpha Technologies Lomain Ni-Cd Pocket Plate Battery - Manual (Page 26)

745-680-B10-001 Rev. A 26
6.0 Charging, continued
6.3 Charge efficiency
The charge efficiency depends mostly on the state of charge of the battery and the ambient
temperature as well as the charging current. For much of its charge profile the Ni-Cd battery
is charged at a high level of efficiency. As the battery approaches a fully charged condition,
the charging efficiency decreases.
6.4 Temperature influence
The electrochemical behavior of the battery becomes more active if temperature increases,
i.e. for the same floating voltage the current increases. If the temperature decreases the
reverse occurs. Increasing the current increases the consumption of water and reducing the
current could lead to an insufficient charging.
For standby application it is normally not necessary to compensate the charging voltage with
the temperature. In order to reduce the water consumption it is recommended to compensate
it at elevated temperature as for example from + 35 °C on by use of the negative temperature
coefficient of −3mV/K and cell.
For operation at low temperatures, i.e. below 0 °C, there is a risk of poor charging and it
is recommended to adjust the charging voltage or to compensate the charging with the
temperature (-3 mV/K, starting from an ambient temperature of + 20 °C).
Example:
A 110 V battery consisting of 90 cells is charged at + 20°C with a 1.41 V/cell float modus
making a total float voltage of 127 V/battery. The same battery will be charged with just 121.6
V/battery at + 40°C and with 132.4V/battery at 0°C.