Gearbox effect on VFD torque limit

[Blue92]

Possible dumb question here, but how does running a motor through a gearbox effect a VFDs ability to limit the torque on the driven load? My gut says the VFD torque limit would be multiplied by the gear ratio, but my gut is often wrong so I figured I would ask here.

Also, if the VFD has a torque limit range of 0-350% (Weg CFW500) how would I go about relating that percentage to desired lb-ft?

10HP motor / 1800RPM
10:1 gearbox w/ 96% efficiency

 

[Steve Bailey]

how does running a motor through a gearbox effect a VFDs ability to limit the torque on the driven load

Not at all. The VFD limits the torque output of the motor. That torque, applied to the gearbox input shaft is multiplied by the gearbox's reduction ratio at the output shaft.
The formula for converting HP to torque is:
Torque = (HP * 5252) / RPM

 

[Blue92]

Not at all. The VFD limits the torque output of the motor. That torque, applied to the gearbox input shaft is multiplied by the gearbox's reduction ratio at the output shaft.
The formula for converting HP to torque is:
Torque = (HP * 5252) / RPM

Thanks! Looks like my gut was right on this one.