Technical information

Malfunction
6-1
1070 080 059-101 (2001.04) GB
6 Malfunction
Although the design of the MF inverters is quite rugged, malfunctions may
occur in a few exceptional cases, e.g. for the following reasons:
D incorrect electrical connection or mains voltage surges,
D insufficient cooling or overload on the MF thyristor unit may trigger the
thermal detector,
D current parameters set are higher than the maximum current permitted or
the monitoring values.
In case of failure, the green LED ”Ready” ⇑ on the front panel of the weld
timer unit goes out. Further information is provided by the diagnostics func-
tion, the error message display on the BOS-5000 operator interface, or a
message on the BT Bosch operator terminal.
DANGEROUS ELECTRICAL VOLTAGE
Danger of life in case of contact with live parts!
Disconnect the system from the mains supply before trouble shoot-
ing or replacing a fuse!
Thermal detector response
The MF thyristor unit contains an NTC thermistor detector, which transmits a
message to the integrated weld timer if the temperature reaches or rises
above
 65° C (+5° C)
If this happens, the weld timer blocks any further sequence.
The green LED ”Ready” on the front panel of the weld timer unit goes out and
the message ”Thyristor unit temperature” is output.
Possible causes Corrective action
Dirt accumulation in heat sink Clean out the heat sink
Excessive ambient temperature Check for sufficient convection.
Checking external forced ventilation
may be required.
Capacity of MF thyristor unit too low Compute duty cycle and check selec-
tion using load diagram (see section
”Notes on Rating”).
No or insufficient cooling water flow Check cooling water inlet and/or tem-
perature.