Siemens SIMATIC S7-400 Reference Manual page 51

Overload at 24 V
In the event of overload at 24 V the output current is electronically limited to a value between
100% and 150% of the rated value. If the voltage then goes below the undervoltage threshold
of 19.2 V (-0/+ 5% corresponds to 19.2 V to 20.16 V), the modules respond as follows:
● For the power supply modules, the 24 V voltage is disconnected and reconnected at a
repeat rate of approx. 0.5 to 1 seconds until there is an output voltage that exceeds the
undervoltage threshold.
● For the power supply modules 6ES7407-0KA01-0AA0, 6ES740x-0KR00-0AA0 and
6ES740x-0KR01-0AA0, the voltage reaches the level determined by the load impedance,
the module is in the characteristic operating range.
After the overload has been eliminated, the voltage returns to the nominal range and the green
24 V LED flashes. The CPU sets the EXTF LED (external fault) and saves the fault in the
diagnostic buffer. You can trigger other responses, such as CPU STOP or a message to a
control room, in OB 81 (power supply error). If OB 81 is not configured, the CPU continues as
normal.
Overload at 5 V
In the event of an overload at 5 V, the power supply modules with 10 A or 20 A output current
can retain an output current of 16 A or 26 A for 300 ms. The power supply modules with 4 A
output current can retain an output current of 6 A for 300 ms. The CPU will then go to DEFECT
afterwards. If the 5 VDC LED flashes on the power supply and can be reset with the FMR
button, you will be able to perform a restart. The CPU will remain in STOP afterwards and will
then require a memory reset.
BAF, BATTF
The following table applies to power supply modules with one battery if the BATT.INDIC switch
is set to the BATT position. It shows the faults indicated and lists how to remedy the faults.
Table 3-8
LED
BAF
H
D
H
D
D = LED is dark; H = LED lights up;
S7-400 Automation System Module Data
Reference Manual, Ausgabe 11/2016, A5E00850736-08
BAF, BATTF; BATT.INDIC LEDs on BATT
LED Cause of fault
BATF
H Battery empty or missing.
No external backup voltage available
H Battery is empty or missing.
Battery stored too long.
External backup voltage available.
D Battery in order.
No backup voltage available (short-cir‐
cuit)
D Battery OK.
External backup voltage available.
Power supply modules
3.5 Fault/Error messages via LEDs
Remedy
Insert new battery. Press FMR button.
Insert new battery. Press FMR button.
Depassivate battery (see
ual ).
● Fault after plugging in a module:
Plugged-in module defective
● Fault after switching on: Remove all
modules and plug in individually
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Installation Man‐
51