DYNAMIS Batterien GmbH
Brühlstr. 15 D-78465 Dettingen / Konstanz
Tel. +49 7735 93669-0 Fax +49 7735 93669-91
[email protected] www.dynamis-batterien.de
04.12.2006
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constant current to maximum voltage until the voltage is leveled up for three hours.
4.6 Thermal runaway phenomena
Thermal runaway is an abnormal phenomenon happened in charging
process, which is shown as a bloated battery. Thermal runaway means a state of
operation where heat generation increases faster than heat dissipation, which may
happen on severe overcharging or electrolyte dry-out. The result is an increase of
the battery's temperature. At elevated temperature, the internal oxygen cycle is accelerated,
and the developed heat causes further increase of the battery temperature. With this self-
accelerating cycle, the thermal runaway is resulted, and the battery will be severely deformed
and bloated. Several precautions are listed as follows
to prevent the thermal runaway:
Avoid the dry-out of batteries: Do not charge at voltage higher than gassing
voltage (2.4V/cell) for too long duration, e.g. >12 hours.
Any defective battery, e.g., the short-circuited or aged battery, in a long
string of batteries should be removed immediately to prevent the
overcharging of other batteries.
The internal oxygen cycle reaction usually happens in the overcharging
stage, where the originally decreasing current density may increase instead of
in the constant-voltage-charging mode. If the cut-off condition for the
charger is relied on the smallness of the current density, this setting may be
too low to be fulfilled when the battery is aged. The charger is continues to
overcharge the battery until the thermal runaway happens.
Always avoid the local overheating of batteries. Be equipped with heat
dissipating devices or temperature sensors in order to stop charging when
necessary.