DC Link Overvoltage
The DC link capacitor voltage exceeds critical protection limits, typically above 850VDC, due to regenerative energy from decelerating motor loads or supply transients. This fault immediately disables SCR firing circuits and activates crowbar protection to prevent catastrophic component failure.
Error Code
F1073
Severity
Fault
Equipment
Soft Starter
Manufacturer
Siemens
Red FAULT LED solid with alternating display showing 'OV' and fault code E45
Immediate motor shutdown with bypass contactor forced open regardless of run command
Oscilloscope shows DC link voltage spikes >850VDC with poor regulation during transients
Audible high-frequency switching noise from crowbar circuit activation
Ground fault indicator may activate due to stress on insulation systems
SCR gate driver outputs disabled showing 0V at gate terminals G1-G6
Motor deceleration too rapid causing regenerative energy feedback through SCRs
Failed DC link capacitor allowing voltage ripple and regulation loss
Lightning or switching transients exceeding varistor clamping capability
Defective crowbar SCR not conducting when triggered above 820VDC threshold
Open circuit in DC link discharge resistor preventing controlled voltage decay
Control PCB overvoltage detection circuit false triggering due to noise
Establish electrical safety boundary and verify equipment isolation using Category IV rated test equipment
Discharge DC link capacitors through 10kΩ resistor until voltage reads <50VDC using isolated probe
Test DC link capacitor bank with capacitance analyzer expecting values within ±15% of 2200µF nominal
Verify crowbar SCR triggering at 820VDC using controlled DC supply and oscilloscope monitoring
Check discharge resistor continuity expecting 47kΩ ±5% resistance across R22 terminals
Replace varistor surge suppressors MOV1-MOV3 if leakage current exceeds 1mA at rated voltage
Validate complete protection system with high-voltage transient test confirming trip at 850VDC ±2%
Safety First: Always isolate power and follow LOTO (Lockout/Tagout) procedures before working on electrical components. If unsure, contact a certified repair technician.
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