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Start current with ABB soft starter


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Im what you might call a newbie to the use & application of soft starters

however I am in the process of installing an Abb PSR 30 soft start to start a 9kw screw conveyor

while the motor is only 9kw the soft start reccomended is rated to 15kw

as the soft start is fitted after the normal contactor & overloads Im wondering if anyone can give

me some idea of what start current I can exspect it to deliver.





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Hello pactrol


Welcome to the forum.


The minimum start current is a function of the motor speed torque curves, motor speed current curves, and the load speed torque curves.


The driven load (in this case a screw compressor) determines the minimum amount of torque required to start.

The motor converts amps into NM and therefore determines the amount of current required to develop the NM required by the load.

There are big differences in loads and in motor performance, so it is not possible to accurately predict what the start current will be without the required information, however from experience, I would expect that provided the compressor is off load at start, it will start with a start current between 350% and 450% of the rated current of the motor. If the compressor is ON load at start, the current will be higher, and if the motor has very poor starting characteristics, it will be higher also.


To learn more about this topic, have a look at the pages on motor starting at http://www.LMPhotonics.com


Best regards,

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