Motor experts...need your advice.

[redshanks]

Is there any difference in torque output if I use a 1725 RPM motor with a larger drive pulley instead of a 3450 RPM motor with a smaller drive pulley to achieve the same final speed? Is there any other downside to using the slower motor with a v-belt and pulley drive system?

 

[Matt Shade]

Horsepower = (Torque (in ft-lbs) X RPM's) / 5252

So a 1 horsepower motor running at 1725 rpms, has 2 times the torque of a 1horsepower motor running at 3450 rpm.

 

[rfrink]

Is there any difference in torque output if I use a 1725 RPM motor with a larger drive pulley instead of a 3450 RPM motor with a smaller drive pulley to achieve the same final speed? Is there any other downside to using the slower motor with a v-belt and pulley drive system?

Good question! It works out to be a wash. It is the old concept of "power-out equals the power-in" (minus any losses). In terms of motor torque, the losses from speed are gained in mechanical advantage from the pulleys...and visa-versa. If you put 2 hp into your machine, you'll get 2 hp out (less losses)...and if the output speed for the 2 cases is the same....then the torque will be the same.


However, 1725 rpm motors are generally a bit heavier than their counterpart 3450 sibling such that the 1725 motor may have a higher current rating ..thus may have a bit more HP. Since motor HP ratings are rounded off such that a motor with say, 1.85hp...will probably be labeled 2hp....and a 2.2 HP motor will also probably be labeled 2 hp. The accurate rating is the nameplate current.