Danfoss VLT AutomationDrive FC 302 fault A7: DC Overvoltage
Alarm 7 on a Danfoss VLT FC 302 is DC Overvoltage: the DC-link voltage exceeded its limit and the drive tripped after a delay. It usually means the motor returned energy to the drive faster than the drive could absorb or dissipate it.
Diagnose this with AI
Try Free Drive Diagnostic Upload a keypad photo, the fault history or a parameter export from your Danfoss VLT AutomationDrive FC 302. InduQT compares the evidence and suggests the next useful checks.
When it happens
- During ramp-down or stopping, especially high-inertia loads
- With an overhauling load driving the motor
- During or after a supply sag
Likely causes and checks
1Ramp-down too fast for the load
- Points to it
- Trips only on stops or speed reductions; Warning 5 DC Link Voltage High may appear first.
- Check
- Lengthen 3-42 Ramp 1 Ramp Down Time or change the ramp type; Danfoss says to choose a ramp-down that avoids overvoltage from regenerative operation.
2No brake resistor, or brake function not active
- Points to it
- Process needs fast stops of a heavy load; 2-10 is Off or no resistor is fitted.
- Check
- Check 2-10 Brake Function and whether a resistor is connected; Warnings/Alarms 25–28 point to a resistor or chopper problem.
3Overvoltage control not enabled
- Points to it
- No resistor fitted and 2-17 is Disabled.
- Check
- Consider 2-17 Over-voltage Control; Danfoss says not to enable OVC in hoisting applications.
4Supply sag
- Points to it
- Trip coincides with a supply disturbance rather than a stop.
- Check
- Danfoss suggests kinetic back-up (14-10 Mains Failure) if the alarm occurs during a power sag.
Telling it apart
- Timing: on deceleration points to regenerated energy; with no stop in progress, look at the supply.
- Warning 5 DC Link Voltage High is the early warning with the drive still running; Alarm 7 is the trip.
- Danfoss also lists increasing 14-26 Trip Delay at Inverter Fault; it notes that protection mode should be disabled in hoisting applications.
Relevant parameters
| Parameter | Name | Why it matters |
|---|---|---|
| 3-42 | Ramp 1 Ramp Down Time | Longer ramp returns energy more slowly. |
| 2-10 | Brake Function | [1] Resistor brake or [2] AC brake; AC brake is less effective than a resistor. |
| 2-17 | Over-voltage Control | Reduces overvoltage trips from generative load; not for hoisting. |
| 14-26 | Trip Delay at Inverter Fault | Delay before tripping on detected overvoltage; Danfoss lists increasing it. |
| 14-10 | Mains Failure | Kinetic back-up for trips during power sags. |
Evidence to collect
- Alarm log time and whether the drive was ramping down
- DC-link voltage (16-30) trend if logged
- 3-42, 2-10, 2-17 and 14-26 settings
- Brake resistor fitted and its value
- Plant supply events at the time
Work on fuel trains, burners, pressure vessels and electrical equipment must be done by qualified personnel following the manufacturer’s documentation and local codes. Never bypass a safety device or interlock.