How Should I View the Speed - Torque Characteristics of AC Speed Control Motors?

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  Mmm...

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  What's wrong, a customer inquiry?

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  Yes I've been asked to select an AC speed control motor and I'm checking the torque characteristics diagram, but I don't know how to read it...

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  You still have a lot to learn! Now, let's check the speed - torque characteristics of the AC speed control motor.

  

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  Which part of this characteristics diagram you don't understand?

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  Honestly, I don't know where to start checking when there are so many lines.

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  Nothing you can do about that. Well then, I'll explain step by step.
  First of all, Figure 2 shows the original torque characteristics of the motor extracted from Figure 1 (for a power supply frequency of 60 Hz).

  

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  So from Figure 2, it means that we can use it as long as it is in the range of (A)!

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  You're so naive, Vex!
  It is true that the torque that the motor can produce is in the range shown in (A), but there is a "safe-operation line" as shown in Figure 3.
  Regarding torque, you have to use within the safe-operation line (B) range.

  

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  Why can't I use the torque that is supposed to be able to produce?

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  That's because the motor generates a lot of heat when operating at a torque above the safe-operation line.
  This safe-operation line indicates the limit of continuous operation without exceeding the allowable temperature of the motor. This means that if you use the motor continuously (30 minutes in the case of a reversible motor) within this range, it will not reach a temperature that could lead to failure (90 °C at the motor case temperature) .

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  I see. When selecting, it is necessary to select a torque value that is below the safe-operation line.
  I'll make the selection right away!

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  Hold on, Vex! I haven't finished explaining the "permissible torque when installing gearheads" yet!
  Look at Figure 4.

  

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  The permissible torque when the gearhead is installed is the permissible torque value of the motor output shaft when the gearhead is combined. Exceeding this value could shorten the lifetime of the gearhead, or cause damage.
  So, the range that can be used with AC speed control motor is (C). The permissible torque of the gearhead output shaft varies depending on the gear ratio, so be sure to check the catalog or website.

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  Okay! Now I know how to read the torque characteristics, I'll go and explain to my customers with confidence!

• February 22, 2021 Updated with the latest information.

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