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Starting Torque


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Hi Marke and others,


I have a conveyor belt which is driven by a 75 kW electric motor powered by a sensorless vector VSD. The VSD has to to be set on high starting toque to be able to breakaway the load at start. We had during the past months several breakdowns of transmission chains. The mechanical guys are complaining that the VSD SET-UP is breaking the transmission chains, which I agree is true as the breakaway torque in such applications is as high as 250 % FLT. There is no way to limit the torque on the VSD as the load did not move for a standard V/F configuration.

It is also amazing to note that once started the output current goes down. We have tried with a 55 k W VSD,configured for high start up torque, but with the same motor but impossible to pull the load at start.


Any guess.



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Hello Bob


it is usual for materials conveyors to require a high breakaway torque. From my experience, around 160% is common. If you supply a lower torque, you will not break the load away.

Ideally, you want to provide a ramping torque rather than a sudden torque application. This can be acuieved using a soft starter, I am not sure with the drive that you are using. The ramping torque enables the conveyor to breakaway in sections and also minimises the torque used to suit the changing load conditions.


Im my book, you either have to reduce the start torque requirement of the load, or you have to strengthen the weakpoints to cater for the torque required.

Have you considered adding a second driving point on to the conveyor, even just to assist the start?


Best regards,

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