Reputable motor manufacturers will show this data in their catalogues for at least 100%, 75% and 50% load. I'd give you my data but it's all in kW, 400v and 50 hz.

Be careful, small motors have bad efficiencies and power factors, and the actual motor may may vary from the published data.

What size shaft are you intending to use? There's no point in going too small. Also if the conveyor stalls the motor you're likely to generate maybe twice full load torque on a three phase motor. ■

Not wishing to doubt your shaft calculations, but the shaft sizes do seem rather large when considering a 1/2 HP (0.37kW) electric motor. Your shafts must be rotating exceedingly slowly? ■

.. exceedingly slow.

Regarding the stalled motor condition (locked rotor), then typically the torque is twice the full load torque. However as this is an "emergency" condition then the factors of safety for the shaft material can be reduced. What strength steel are you using for the shaft?

Also this thread may be of assistance --

https://forum.bulk-online.com/showth...&threadid=8237 ■

You don't have a lot of alternatives, but I think you are on the right track by limiting the current to the drive. However, be sure to label your equipment properly. Otherwise, the first time it stalls out on graveyard shift, the night electrician will wonder why it has such small overloads and install the proper ones.

If you want to be safe .... compromise! Use a higher grade of steel to minimize shaft size; turn your shaft down one size at the bearings to minimize bearing size; install a shearpin hub or slip clutch (Oh! I hate to suggest that!); use a hydraulic drive where pressure and flow can be controlled. ■

With belt conveyor drive pulleys shaft size is often defined by deflection so high strength steels can be a waste of money. ■

Your dilema is due to doubt (possibly legitimate) that your calculatrions reflect reality. Why else would you choose such oversize in your motor? Having chosen the oversized motor what makes you think that its full loading or (higher yet) stalled torque will be incurred? If your belt (take-up) tensions are set according to your calculations then the drive pulley will slip at the belt before developing the 7-fold (full motor load) or 14-fold (max motor starting) torque. You need to bound your analysis realistically including factors that reflect the range of uncertainty for small applications (maybe two-fold, not 7-fold or 14-fold). Once you establish this realistic criteria then treat it with certainty and size your shafts accordingly. Running loads are the only loads that matter as these determine fatigue and life. Start-up loads are not so important as they don't typically approach yield stress levels, and the number of starts don't typically threaten fatigue failure.

Joseph A. Dos Santos ■

.... yeh, life can be a real pain!! ■