Motor hunting up and down or measured value fluctuates — Controller instability

What does Motor hunting mean?

The Grundfos MAGNA3 pump motor's speed fluctuates erratically (referred to as 'hunting'), or the measured values on the display become unstable. This indicates that the pump's PI controller settings (gain and integral time) are not optimally tuned for the specific system, leading to operational instability.

• The gain (Kp) value in the controller settings is too high for the system dynamics.
• The integral time (Ti) value in the controller settings is too low for the system.
• Controller settings significantly deviate from factory defaults or recommended guidelines for the application.

Click steps to track your progress.

1. 1

   Access the 'Controller settings' menu on the pump's display or through the Grundfos GO app.

2. 2

   If the controller is hunting or unstable, dampen the system by gradually reducing the gain (Kp) or increasing the integral time (Ti) values.

3. 3

   If the controller is too slow-reacting, try to gradually increase the gain (Kp) to improve responsiveness.

4. 4

   As a guideline, set the gain to half the value that caused the motor to become unstable, and the integral time to twice the value that made the motor unstable, as described on page 30.

5. 5

   If adjustments do not resolve the issue, revert to the factory default settings for gain (Kp=1) and integral time (Ti=8) for other control modes and re-evaluate the system's behavior.