Alpha Technologies Industrial Ni-Cd Batteries Standard Range - Manual (Page 18)

18 EN-ALPHA-TMSR-001 (10/09)
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5.6 Floating Effect -Voltage Depression
When a Ni-Cd battery operates at a fi xed fl oating voltage over a certain period of time, a decrease of the voltage
level of the discharge curve occurs. It begins after one week and reaches its peak in approximately 3 months.
Since this effect reduces the voltage level of the battery it can be considered as reducing the performance and
autonomy of the battery as well. Therefore, it is necessary to take this effect into consideration when sizing a
Alpha Ni-Cd battery. The Alpha calculation program gives the possibility to include this factor into the customer’s
calculation.
The fl oating effect is a reversible effect and can only be eliminated by a full charge/discharge cycle. Please
note that it cannot be prevented by just a boost charge. The Alpha battery sizing program provides the option to
calulate with and without this fl oating effect enabling the customer to se the added benefi t. Our recommendation
is to always include this fator when sizing a battery.
5.0 Battery Sizing, continued
Graph 5-1, Floating derating factor as a function of discharge time
1.10
1.00
0.90
0.80
0.70
0.60
0.50
0.40
0.30
1 5 30 60 5 10 15 20 30 1 1.5 2 3 5
time[hours] time [sec] time [min]
The graph above illustrates the level of discharge for a KM 110 P cell discherged for 30 minutes with a
current of 91A to 1.10V/cell according to discharge table. This value is correct after the battery has been
fully charged via constant cuttent charging.
If the cells are charged via fl oat charging, the discharge time must be reduced by a factor of 0.74. This
results in a discharge time of 22.2 minutes.
This fact will be automatically considered by the Alpha battery calculation program if this option is chosen.