
Power supply modules
3.5 Fault/Error messages via LEDs
S7-400 Automation System Module Data
62 Reference Manual, Edition 09/2009, A5E00850736-06
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 BAF, BATTF; BATT.INDIC LEDs on BATT
LED
BAF
LED
BATF
Cause of fault Remedy
H H Battery empty or missing.
No external backup voltage available
Insert new battery. Press FMR button.
D H Battery is empty or missing.
Battery stored too long.
External backup voltage available.
Insert new battery. Press FMR button.
Depassivate battery (see
Installation
Manual
).
H D Battery in order.
No backup voltage available (short-
circuit)
Fault after plugging in a module:
Plugged-in module defective
Fault after switching on: Remove all
modules and plug in individually
D D Battery OK.
External backup voltage available.
-
D = LED is dark; H = LED lights up;
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