Overload Protection in Low Speed Range

What does E38. mean?

This fault occurs when the inverter's built-in electronic thermal function detects an overload specifically during operation in an extremely low speed range (0.2 Hz or lower). This indicates that the motor is experiencing excessive load at low speeds, where cooling efficiency might be reduced, or that thermal parameters are not correctly configured for low-speed conditions.

• Motor operating at very low speeds (e.g., <0.2 Hz) with high torque demands, leading to poor motor cooling and excessive current.
• Motor selection is undersized for the application, especially at low speeds where the motor's integral cooling fan efficiency is significantly reduced.
• Electronic thermal overload settings (e.g., P2-01, P2-02, P2-03) are not accurately optimized for low-speed operation or the specific motor characteristics.
• Mechanical binding, excessive friction, or misalignment in the driven load, increasing the torque required from the motor.
• Inadequate motor cooling conditions (e.g., motor fan blocked, dust accumulation on motor fins) exacerbating overheating at low speeds.

Click steps to track your progress.

1. 1

   Measure the actual motor current during low-speed operation using a clamp meter and compare it to the motor's rated current (P2-01) and service factor.

2. 2

   Verify motor parameter settings P2-01 (Motor Rated Current), P2-02 (Motor No-Load Current), and P2-03 (Motor Overload Protection Curve) are accurately set for the motor.

3. 3

   Inspect the mechanical load for any binding, excessive friction, or misalignment that would increase the motor's torque demand unnecessarily.

4. 4

   Ensure the motor's cooling fan (if present) is operational and that the motor's cooling fins are free from dust and debris, particularly for totally enclosed fan-cooled (TEFC) motors.

5. 5

   Consider increasing the inverter's electronic thermal overload setting (e.g., P2-03) or modifying the V/f pattern (e.g., C3-02, C3-03) to boost voltage at low frequencies if motor saturation is suspected.