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What should be done if a motor is vibrating when running on an AC drive at or above a certain frequency or speed?

The most common cause of motor vibration that is associated with a certain speed is mechanical. Check for loose belts, dampers, broken parts, foreign materials, bad bearings, incorrectly adjusted or missing fan blades or other similar issues.

In some applications such as fans or air handlers, the vibration may be due to a natural harmonic frequency due to the shape and size of the fan and ductwork. In these cases, there may not be any practical physical adjustments to make. In this case, it may be possible to utilize skip or jump frequency features in the drive to avoid running at speeds that cause vibration.

Another possible cause for vibration is drive adjustments. It could be that the drive is set up to regulate the speed too tightly. Most drives have stability, frequency loop gain or damping adjustments. It may be necessary to adjust these parameters.

Another thing to check is the drive adjustments for motor parameters. Make sure the nominal voltage, amperage, frequency and power factor adjustments match the motor nameplate. If the drive has autotune, use it to tune the settings.

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