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6
Malfunction
Thermal detector response
1070 080 058-101 (2001.04) GB
Although the design of the thyristor power units 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 thyristor power 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 Bosch BT operator terminal.
DANGEROUS ELECTRICAL VOLTAGE
Danger of life in case of contact with live parts!
Disconnect the system from the mains supply before troubleshoot-
ing or replacing a fuse!
The thyristor power unit contains a thermostatic switch, which transmits a
message to the integrated weld timer if the temperature reaches or rises
above
80° 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
Dirt accumulation in heat sink
Excessive ambient temperature
Capacity of thyristor power unit too low Compute duty cycle and check selec-
No or insufficient cooling water flow
Malfunction
Corrective action
Clean out the heat sink
Check for sufficient convection.
Checking external forced ventilation
may be required.
tion using load diagram (see section
"Notes on Rating").
Check cooling water inlet and/or tem-
perature.
6-1
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