danfoss w7 alarm
Danfoss VFD, Warning 7 (or Alarm 7) stands for DC Overvoltage. This means the voltage in the drive's internal DC link (the "intermediate circuit") has exceeded the safety limit. While a Warning 7 means the drive is still active but at its limit, an Alarm 7 will cause the drive to "trip" and stop the motor to prevent hardware damage.
Common Causes
Regenerative Braking (Most Common): When a motor slows down a heavy or high-inertia load too quickly, the motor acts like a generator and pushes energy back into the drive, raising the DC link voltage.
Ramp-Down Time Too Short: The deceleration time is set too aggressively for the load.
Mains Supply Issues: The incoming AC line voltage is too high or has a "spike."
No Brake Resistor: The application requires a brake resistor to dissipate excess energy, but one is either not installed or not working.
How to Fix & Troubleshoot
1. Extend the Ramp-Down Time
The simplest fix is to let the motor coast to a stop more slowly.
Increase Parameter 3-42 (Ramp 1 Ramp Down Time). If it's currently at 3 seconds, try increasing it to 10 or 15 seconds.
2. Enable Overvoltage Control (OVC)
Danfoss drives have a built-in feature that automatically extends the ramp-down time if it detects the voltage getting too high.
Go to Parameter 2-17 (Overvoltage Control).
Change it to [2] Enabled.
3. Check/Install a Brake Resistor
If your application requires fast stops (like a crane or a high-speed conveyor), you cannot just extend the ramp time. You likely need a brake resistor.
If you already have one, check the wiring and measure the resistance to ensure it hasn't burned out.
Ensure Parameter 2-10 (Brake Function) is set to [1] Resistor Brake.
4. Verify Incoming Voltage
Check the LCP display or use a multimeter to check the DC link voltage.
For a 400V drive, the DC link should be around 540V DC at rest ().
The trip limit is usually around 800V DC. If your resting voltage is already very high (e.g., 750V), your incoming AC power may be the problem.
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