Why so large?

[ptonsparky]

We are finally making corn flakes. The largest motor is a 60 on one mill and 75 on the other. These motors turn a pair of solid flake rollers that are about 18" diameter by 30" long. At full production these motors only draw about 23 A each. PFC is at each motor. Amperage to turn just the rollers is 6-12 amps, with no product.

Are the motors this large just to get the rollers turning? It appears a 25 HP would have been adequate once the rollers are up to speed.

(Amp meters used are not true RMS and current is recorded every 5 seconds to develop a trend line)

 

[Cow]

The large feedlot I do work for also has 60HP roller motors, but I've never amped them. I couldn't tell you why yours are running such low amperage, your theory of using 60HP motors just to get the rollers up to speed might be why though.

 

[Jraef]

We are finally making corn flakes. The largest motor is a 60 on one mill and 75 on the other. These motors turn a pair of solid flake rollers that are about 18" diameter by 30" long. At full production these motors only draw about 23 A each. PFC is at each motor. Amperage to turn just the rollers is 6-12 amps, with no product.

Are the motors this large just to get the rollers turning? It appears a 25 HP would have been adequate once the rollers are up to speed.

(Amp meters used are not true RMS and current is recorded every 5 seconds to develop a trend line)

Motors are sized for torque at a given speed, true, this can be thought of as the Load Torque. So the Full Load Torque output of the motor must be at least equal to the Load Torque required. But also the motor must provide for accelerating torque. A motor can supply Break Down Torque to accomplish this, but only for a very short time. The game plan for the ME is to calculate the AAT, Average Accelerating Torque requirement, meaning mainly the EXTRA torque above and beyond the load torque requirement in order get to full speed before the motor current causes the motor temperature to enter the Thermal Damage Curve. The larger the mass that must be accelerated, the larger the AAT requirement, which often results in the motor appearing to be larger than necessary.