Danfoss AL 13 Fault — What It Means
Alarm 13 on a Danfoss FC302 VFD signals overcurrent where the drive’s output current has gradually built beyond its rated capacity (typically 150 to 160 percent of nominal current) for several seconds. This is distinct from an instantaneous short circuit fault. The drive detects the motor drawing too much current during normal operation or acceleration, usually because the motor shaft is mechanically overloaded, motor parameters (especially nominal motor current in parameter 1-24) are set incorrectly, or a motor winding has developed a partial short.
Cable issues between the drive and motor can also trigger AL 13. Loose connections create resistance that causes current spikes. Inside the drive, aging IGBT modules or failing DC bus capacitors can lose current regulation ability. Short deceleration times on high-inertia loads or incoming line voltage running more than 10 percent above nominal can push the system into fault territory.
Before You Replace Anything
Technicians often replace the IGBT inverter module before checking motor settings and connections. Always disconnect the motor and run the drive unloaded first; if AL 13 clears, the fault is motor-side and the drive electronics are fine.
Common Causes
- Wrong motor current setting (~30%) Parameter 1-24 (nominal motor current) does not match the motor nameplate, causing the drive to fault on normal load current.
- Mechanical overload on motor shaft (~25%) The motor is driving a seized bearing, jammed conveyor, or other stuck load that forces current draw beyond rated capacity.
- Loose or corroded motor cable connections (~20%) High resistance at terminals between the drive and motor causes voltage drop and current spikes that trip the overcurrent alarm.
- Failing IGBT modules in the inverter (~15%) Aging or damaged IGBT transistors lose current regulation ability and allow uncontrolled current flow to the motor.
- Motor winding partial short (~10%) Insulation breakdown inside the motor creates a turn-to-turn short that draws excess current without mechanically stalling the shaft.
Quick Diagnosis
Answer these to narrow it down fast.
Does AL 13 clear when you disconnect the motor and run the drive unloaded?
No: The drive has an internal component failure (IGBT modules or DC bus capacitors). Proceed to voltage and IGBT diagnostics.
Are all three input phases within 3 percent of one another when measured with a voltmeter?
No: If the low-phase position moves when you swap wires, the supply is unbalanced. If it stays in the same position after swapping, the VFD rectifier section is faulty.
Does the motor shaft spin freely by hand with power off and motor disconnected?
No: Mechanical overload is present. Free the load, repair bearings, or remove obstructions before restarting the drive.
Step-by-Step Fix
- Disconnect the motor from the drive output terminals (U, V, W) and run the drive unloaded to isolate whether the fault is internal to the drive or on the motor side.
- Verify motor data in parameters 1-20 through 1-25, especially parameter 1-24 (nominal motor current), matches the motor nameplate exactly.
- Check all cable connections from drive output terminals to motor windings for tightness and corrosion, then measure continuity through each phase.
- Measure incoming line voltage at all three input phases with a voltmeter and confirm they are within 3 percent of one another; swap the low-phase wire and retest to determine if the supply or rectifier is at fault.
- Extend deceleration time in parameter 2-10 if the load has high inertia and the fault occurs during ramp-down, which can cause regenerative current spikes.
- Test IGBT modules on the inverter board with a multimeter in diode-check mode if internal fault is suspected after unloaded test; replace the inverter IGBT assembly if shorted.
- Inspect DC link capacitors on the DC bus board for bulging, leaking, or exploded cases; replace the capacitor bank if damaged, as spikes cause overcurrent trips.
Parts Often Needed
| Part | Notes |
|---|---|
| Danfoss FC302 IGBT inverter module | Amazon | Match the part number to your drive’s power rating and voltage class (consult the FC302 parts manual) |
| DC bus capacitor bank for Danfoss FC302 | Amazon | Specify drive frame size and DC voltage rating when ordering |
When to Call a Pro
Call a qualified VFD technician or industrial electrician if the drive continues to fault after you correct motor parameters and verify cable connections. High-voltage DC bus work, IGBT module replacement, and inverter board diagnostics require specialized meters, safety training, and knowledge of power electronics. If the motor itself has a winding short, a motor shop will need to rewind or replace the stator. Attempting IGBT or capacitor replacement without proper lockout/tagout and DC bus discharge procedures can result in lethal electric shock or arc flash injury.
Rough cost: A pro service call runs about $200-800 depending on whether it is a parameter correction, cable repair, or IGBT module replacement.