22 Installation Instructions MB-Secure 1000/2000/3000/4000/5000/6000
3.7 Calculation of accumulator capacity
To calculate the accumulator capacity required, the overall system current consumption must be known. The
current consumption is determined by measuring consumption with accumulator(s) connected when there is no
power supply.
For systems of VdS Class C, a bridging time of 60 hours is prescribed in the case of power failure.
For a current consumption of 250 mA, for example, the required accumulator capacity is calculated as follows:
60 hours x 250 mA = 15 Ah.
Accumulator capacity selected: 2 x 10 Ah = 20 Ah.
If sirens or a flash lamp, for example, are used as signaling devices, allowance can be made for the
“reserve energy” to activate the signaling device by increasing the total current consumption by 1 mA.
With this, we have following calculation:
60 hours x 251 mA = 15.06 Ah.
The accumulator capacity selected remains sufficient.
3.8 Connection of multiple power supply/charger units
Please note that when multiple power supply/charger units are connected together, the operating
voltage can be variably high in case of power failure, since accumulator voltage charging is temperature
dependent. This can lead to an undesired flow of current to control and signal lines. Therefore, only
external devices that are electrically isolated from the operating voltage should be used.
Diagram Multiple power supply units
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