Increasing speed of 50hp motor

[rockman7892]

I have a 50hp (480V) motor used on a radial stacker conveyor to convey rock to the top of the conveyor. The motor shaft is coupled with belts (sheaves) to the head pully of the conveyor. People where want to increase the speed of the conveyor by mechanically changing the sheaves. Right now I am measuing 51A on the motor, which has a FLA of 62A when the belt is fully loaded.

My question is if we mechanically change the speed of the conveyor what effect this will have on the motor? I obviously expect the current to increase but am wondering what the factor causing it to increase will be and if there is a way to determine how much. Will the current increase because by mechanically changing the speed of the conveyor more torque will be required by the motor? Is there a way of determining how much of a current change can be expected from increasing the speed and therefore the amount of material on the belt?

 

[rockman7892]

Ok, from looking at all of the calculators and equations I can see how speeding up the belt would not have any effect on the hp of the motor and therefore we can speed if up without expecting to draw additional current on the motor. This is all assuming that our feed rate stays the same.

If we do change the feed rate, or increase the tph then the hp on the motor will increase, and we have enough room for about an 11% hp icrease (maybe more) however that may relate to the given loading?

The only other question that I have is, how will that starting current be effected by speeding up the belt? Normal current will not be effected, but will the starting current be effected?

 

[jraef]

Yes, if you increase the infeed rate, then for sure your TPH will go up and your load on the second belt will increase, so you will then need more HP.

Loaded restart starting current will definitely be affected because it will take longer to get the load on the belt up to speed with the higher final speed. The peak may not necessarily increase because there will be a lower pile, less material, lower moment of inertia, so less torque needed. But the thermal I²t effects on the motor (and therefore starter OL relay) will probably be noticeable. For an unloaded start, you may not notice the difference.