Why my frequency converter go only to 2.5Hz?

FAQ #101958

It could be that the motor consume too much current.

In this special case the motor was already working several years without frequency  converter under a roof. The circumstances of the weather involving that the isolation isn't god enough and the motor use too much energy.

Solution:

Every time when you connect an old motor with a frequency converter, connect between the devices a sinus filter to avoid such kind of problem.