DC Link Overvoltage
The DC link voltage across the main bus capacitors has exceeded critical protection limits, typically 850-900V for 480V input systems. This fault is similar to bus overvoltage but specifically indicates excessive stored energy in the DC link circuit that could damage power semiconductors. The condition usually results from regenerative energy that cannot be properly dissipated through braking circuits or supply feedback.
Error Code
AL80
Severity
Fault
Equipment
AC Drive / VFD
Manufacturer
Danfoss
Immediate drive shutdown with F003 or DC Link OV fault code displayed prominently on operator interface
Drive trips during deceleration phases especially when stopping high-inertia loads or descending vertical applications
DC link voltage measurement exceeds 850V when checked with high-voltage differential probe across main capacitor bank
External braking resistor glows red hot or thermal protection of brake unit activates during fault conditions
Motor produces jerky or erratic motion during deceleration as drive attempts to manage excess regenerative energy
Capacitor bank temperature rises significantly above normal 40-50°C operating range measured with IR thermometer
Insufficient braking resistor wattage rating or duty cycle for application requiring more than 20% continuous regenerative power handling
Failed braking IGBT or chopper transistor preventing discharge of DC link energy through external braking circuit
Excessive deceleration rates programmed in drive parameters creating regenerative power beyond system capability to dissipate
High supply voltage combined with light loading causing DC link voltage to approach upper operating limits during normal conditions
Defective DC link discharge circuit including bleeding resistors or discharge contactors failing to operate during shutdown
Drive undersized for application regenerative requirements particularly in vertical lift or high-inertia rotating equipment
Apply comprehensive LOTO: disconnect main power, external braking connections, and verify DC link discharge below 50V before any contact with internal components
Calculate regenerative power requirements: P_regen = 0.746 × HP × efficiency × (decel time/cycle time) and verify braking resistor rating exceeds this by 25%
Test braking IGBT with curve tracer or substitute known-good component - gate threshold should be 4-6V with collector-emitter leakage under 5mA
Measure braking resistor value (typically 27-150 ohms depending on drive size) and inspect for thermal damage or carbon tracking on ceramic insulators
Adjust deceleration parameters to extend ramp times and reduce peak regenerative power - typically increase decel time by 50-100% from default settings
Install or upgrade external braking unit with proper power rating if internal brake resistor is inadequate for application duty cycle
Perform regenerative load test with dynamometer or actual load to verify proper energy dissipation during normal deceleration cycles and confirm DC link voltage remains below 820V
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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