ermining the compact stations
Determining the batteries and power supply
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11.3.4 Determining the power supply of the stations
11.3.4.1 Calculating the total current values
The power supply is determined by the total current consumption (I
total
).
The total current consumption depends on the following factors:
● Operating current in alarm condition
● Operating current in quiescent condition
● Charging current of the battery (battery capacity)
In alarm condition the batteries may be uncharged. For this reason the total current
consumption for the alarm condition and the quiescent condition must be
calculated separately. The higher of the two total current consumption values is
taken into consideration for selecting the power supply.
Calculating the total current consumption in alarm condition
The power supply in alarm condition must be calculated so that the higher current
consumption of all consumers can be covered. As only a small percentage is for
charging the battery, or the battery may be uncharged, the charging current does
not have to be taken into account.
I
total_A
= 1.1 * I
A total
Calculating the total current consumption in quiescent condition
The power supply in quiescent condition must be calculated so that recharging of
the battery is ensured. For this reason the charging current is included.
I
total_R
= (1.1 * I
R total
) + I
L
Calculating the charging current of the battery
According to EN 54-4, a discharged battery must be recharged to 80 % of its
capacity within 24 hours. The following calculation therefore applies for the
charging current.
I
L
= K
Batt
/ 20
I
L
Charging current [A]
K
Batt
Battery capacity [Ah]
20 Constant [h]
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