Alpha Technologies Industrial Ni-Cd Batteries Standard Range - Manual (Page 12)

12 EN-ALPHA-TMSR-001 (10/09)
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4.1 Capacity
The capacity of nickel-cadmium batteries is rated in ampere-hours (Ah) and is the quantity of electricity at +20 °C
(± 5 °C) which can supply for a 5 hour discharge after being fully charged for 7.5 hours at 0.2 C5. These fi gures
and procedures are based on the IEC 60623 standard.
According to IEC 60623, 0.2 C
5
A is also expressed as 0.2 I A. The reference test current is expressed as:
I
t
A= C
n
Ah
1 h
Where:
C
n
is the rated capacity declared by the
manufacturer in ampere-hours (Ah)
and:
n is the time based in hours (h) for which
the rated capacity is declared
4.2 Cell Voltage
The cell voltage of a Ni-Cd cell is the result of the electrochemical potentials of the nickel and the cadmium
active materials in cooperation of the potassium hydroxide electrolyte. Therefore, the nominal voltage for this
electrochemical couple is 1.2 V. From the electrochemistry of the reaction given above (see point 3) the free
voltage of 1.3 V is given for the Ni-Cd cell. This voltage is also observed directly after charging of the cell.
4.3 Internal Resistance
The internal resistance of a Ni-Cd cell is very diffi cult to measure and to defi ne since it varies with different
temperature and state of discharge. The internal resistance also depends on the cell type and size as well as
it increases for lower state of charge. Apart from this the internal resistance of a fully discharged cell no carries
weight. Reducing the temperature also increases the internal resistance. The correct values regarding the special
conditions can be provided by our technical staff.
4.0 Operating Features