Low-Speed Overload Protection

What does E38 mean?

This fault indicates an overload condition detected when the motor is operating at very low speeds. The inverter's protection mechanism trips to prevent motor damage that can occur when operating heavy loads at low frequencies, where cooling efficiency might be reduced and current demand is high.

• Motor operating at very low speeds with excessive mechanical load, leading to reduced motor cooling capacity and increased slip.
• Inverter's low-speed overload protection curve (P5-04) set too aggressively or not matched to the application's motor characteristics.
• Mechanical binding or excessive friction in the driven equipment, increasing required motor torque at low speeds.
• Motor characteristics not correctly entered into the inverter (e.g., P2-01, P2-03), causing miscalculation of actual motor load.
• Insufficient motor sizing for the application, especially when requiring continuous low-speed, high-torque operation.

Click steps to track your progress.

1. 1

   1. Measure actual motor current (A) at the operating low speed and compare to the motor's rated current (P2-03) and inverter's low-speed protection curve (P5-04).

2. 2

   2. Inspect the mechanical system for binding, worn bearings, or any resistance that significantly increases torque demand at low speeds.

3. 3

   3. Review and adjust the low-speed overload protection parameter P5-04 (Low speed overload gain) to better match motor thermal characteristics and application requirements.

4. 4

   4. Verify all motor nameplate parameters (P2-01 Motor rated power (kW), P2-02 Motor rated voltage (V), P2-03 Motor rated current (A), P2-04 Motor rated frequency (Hz), P2-05 Motor rated speed (rpm)) are accurately programmed into the inverter.

5. 5

   5. Consider improving motor cooling (e.g., adding an independent cooling fan) or upsizing the motor/inverter if continuous low-speed heavy loads are required.