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Motor selection

  1. Sep 12, 2005 #1

    i need a variable speed motor. I came across a catalog which has a motor with a base speed of 1800rpm and power of 1hp and it is of a variable torque type.

    What does base speed means here? Does it means it allows speed from 0 to 1800rpm? and does its power of 1hp is constant for various rpm and torque?

    So for example if the output is at 300rpm, could i safely assume that the torque is = 1hp/300rpm? likewise for say 500rpm, its torque is 1hp/500rpm?

    thanks for advice

  2. jcsd
  3. Sep 12, 2005 #2
    Okay, as a good standard metric, the power output of a motor is proportional to the cube of the rpm. So your engine, as described, delivers 1 hp AT 1800 rpm. Using the cube metric, the engine should deliver about 0.005 hp at 300 rpm and 0.02 hp at 500 rpm.

    You are correct in that the power divided by the rpm is the torque. So the engine should deliver (using the above values) 18 ft*lb at 1800 rpm, 0.5 ft*lb at 300 rpm, and 1.4 ft*lb at 500 rpm.

    Hope that helps.

  4. Sep 12, 2005 #3
    inverter motor


    i have a variable speed motor and i would like to control its speed electronically, does an ac control such as an inverter works?

    any idea how should i go about doing it? do i select my motor first then the controller comes later?
    wat specifications about the controller should i take note of?


  5. Sep 13, 2005 #4


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    You're obviously starting on the ground floor when it comes to electric motors and drives. There are usually two applications of a motor: cconstant power and constant torque. Of course there are hybrids between the two, but usually you can limit your focus on these points.

    The major thing you need to do is determine what kind of performance you need from your motor. Size power range, speed range etc...I would highly recommend that you start searching for literature on the topic. There are a lot of factors to look at when selecting a motor-drive combination. The motor is usually the easier part to select IMO. The drive is where you can really detail how you want the motor to operate. A good first step will be with a set of papers, called the Cowern Papers. They are written by Ed Cowern who works for Baldor. They cover a lot of the basics and will get you on your way.

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