Constant Torque vs Constant Horsepower

This topic contains 4 replies, has 2 voices, and was last updated by  Glenn Adkins 5 months ago.

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  • #9963

    Glenn Adkins
    Participant

    I have seen both in here but don’t understand the difference, I thought it had to be 1 or the other, what is the difference?


  • #9964
    John C
    John C
    Galco Representative

    Hello Glenn, this is a good question.
    Any drive capable of taking a motor above it’s base speed also does both Constant Torque and Constant Horsepower. It has to do with the speed range you are operating the motor in. Most all electric motors (AC or DC) will list their Base speed rating on the name plate. However you have to understand that the Base speed is not necessarily the Max speed rating. This is not usually listed on the name plate but might be. You may have to contact the Mfg of the motor to find out what the max speed rating is. If you plan on using your motor above base speed you better make sure what the max rating. OK so now I have established 2 speed ranges a motor can operate in, 0 to Base speed, and Base speed to Max speed. With AC or DC motors, the 0 to Base speed range is the Constant Torque range, and Base speed to Max speed is the Constant Horsepower range of operation, ok?


  • #9965

    Glenn Adkins
    Participant

    Ok this helps a little but why is it constant horsepower to max speed


  • #9966
    John C
    John C
    Galco Representative

    Well another good question. I will explain this separately for AC and DC so you can see the difference and the similarity’s in many different drives.
    In AC drives there is something called “Volts to Hertz” ratio. For Constant Torque operation the output voltage to the motor is maintained proportional to the Hertz by the Firmware on the Main Control board of the drive. It can usually be modified a little but for the most part at 25% Hertz you have 25% voltage, at 50% you have 50% and so on to 100% of Base speed. So lets say it is a 460 volt motor at 60Hz, this means that 50% is 30Hz and 230 volts, so now lets go above 60Hz to 90Hz. Now the drive is going to maintain the voltage at 460 volts from 60Hz to 90Hz and what happens in the motor is the speed goes up, the voltage stays the same, and the torque goes down. Same thing in a DC motor, the speed goes up, the Armature voltage stays the same and the torque goes down to Max speed, this makes Constant Horsepower.


  • #9967

    Glenn Adkins
    Participant

    Ok I think I get it now, thank you


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