
General specifications
1.1 Standards, certificates and approvals
S7-400 Automation System Module Data
26 Reference Manual, Edition 09/2009, A5E00850736-06
CuULu requirements for hazardous location on the battery power supply for CPUs
The power supply to the backup battery of a CPU must be via a fire-resistant plug. The figure
below portrays the concept of such connection.
1 2
(1) Battery or voltage supply
(2) CPU with "Ext. Batt." connector
Figure 1-1 Power supply to the backup battery
The following conditions apply to the performance characteristics of this connection:
Voc (no load voltage) = 15V Vmax = 15V
Isc (short-circuit current) = 50 mA Imax = 50 mA
Ca = Battery/voltage supply capacity Ci = 25 nF maximum
La = Battery/voltage supply inductance Li = 2 mH maximum
The battery/voltage supply which provides the fire-resistant connection must have the
following values:
Battery/Power supply CPU input "Ext. Batt." with cable
Voc ≤ Vmax (15V)
Isc ≤ Imax (50 mA)
Ca ≥ Ci + Cc (25nF + Cc)
La ≥ Li + Lc (2mH + Lc)
Cc = Cable capacity
Lc = Cable inductance
The batteries used must have the following properties:
● Battery technology: Li/SOCL2
● Model: AA
● Voltage: 3.6 V
The batteries stipulated by Siemens fulfill requirements that go beyond the ones mentioned
above.
You may only use batteries approved by Siemens!
Note
If you do not know the capacity and inductance of the cable, you can use the following
values:
Cc = 197 pF/m (60 pF/ft.), Lc = 0.66 pF/m (0.2 mH/ft)
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