Back EMF too high

What does WARNING 127 mean?

This warning, specific to PM motors, indicates that the back electromotive force (EMF) voltage has exceeded 90% of the inverter's maximum voltage threshold (U invmax) and has remained high for over 5 seconds. This condition suggests that the motor is generating excessive voltage, potentially due to overspeeding or regenerative braking issues, which could lead to overvoltage trips.

• Motor rotation speed exceeding the drive's operational limits, generating excessive back EMF (e.g., above 90% of U invmax).
• Regenerative operation (e.g., braking a high inertia load) feeding excessive energy back to the DC link, raising its voltage beyond acceptable levels.
• Incorrect motor nameplate data (e.g., Parameter P1-20 'Motor Nominal Voltage', P1-21 'Motor Nominal Frequency') entered into the drive, leading to miscalculation of expected back EMF.
• Oversized PM motor for the application, where even moderate speeds generate back EMF approaching the drive's voltage threshold.

Click steps to track your progress.

1. 1

   Measure actual motor shaft speed (RPM) with a tachometer and compare it against the motor's rated maximum speed and the drive's configured maximum output frequency (e.g., Parameter P2-01).

2. 2

   Review and increase deceleration ramp times (e.g., Parameter P3-02 'Ramp 1 Down') to reduce regenerative energy during braking sequences.

3. 3

   Check and correct all motor nameplate data in drive parameters, specifically P1-20 (Nominal Voltage), P1-21 (Nominal Frequency), and P1-22 (Nominal Current).

4. 4

   If regeneration is persistent, consider installing or verifying the operation of a dynamic braking resistor (DBR); check DBR connection at terminals R+/R- and resistance value.

5. 5

   Monitor the DC link voltage via the drive display (e.g., Parameter P0-01 'DC Link Voltage') during operation to observe peak values.