Help with stepper motor/PSU specs


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  1. #1
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    Question Help with stepper motor/PSU specs

    Looking at these two motors:

    NEMA23 270oz/in 2.8A Stepper Motor ¼” Dual Shaft (KL23H276-28-4B)
    NEMA23 425oz/in 2.8A Stepper Motor ¼” Dual shaft (KL23H286-20-8B)


    It has been suggested that I should get a 48V/7.3A power supply instead of a 36V/9.7A power supply, because higher voltage means better torque.

    I am trying to calculate what the maximum current draw will be for the entire system, but the more I think about it the less it makes sense.

    At what voltage is that 2.8 amp rating on the motor for?

    The only voltage listed on the spec sheets are 3.2V & 4.17V, respectively. That does fit when you plug in the rated ohms value of its resistance; 2.8A x 1.13ohm = 3.2V and 2.8A x 1.5ohm = 4.2V.

    But nobody actually runs these motors at that voltage, they are sold with a 36V psu and I am being told to go 48V. Given the linear relationship of ohms law would I would assume that at 48V each motor will draw (48V/1.5ohm) = 32A? That would certainly burn out the power supply! But I know for a fact that a ~9A power supply is enough for 3 of these things at 36V...

    So how do I determine exactly what current these motors will draw at higher voltages, and if my PSU is adequate?


    Thanks!

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    Similar Threads:
    Last edited by cds333; 01-04-2019 at 05:09 PM.


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    Default Re: Help with stepper motor/PSU specs

    The driver reduces the voltage supplied to the motor winding so the maxiumum current is newer more than 2.8A. Because of back emf in electric motors you need to supply higher voltage when the motor is turning fast. That is beacuse you should use 48V so the driver manages to deliver 2.8A (and thereby sufficient torque) at higher speeds. So maximum theoretical power you get out from a motor is U*I which in your case is 2.8A and 48V = 134W. With 3 axes you have a total maximum consumption of 403W. In practice you need about 50-70% of this because they newer draw maximum at the same time and the real maximum power available per motor will be a bit lower. So the 7.3A power supply is sufficient.

    Btw. For best speed/torque curve you should use motor with lower inductance. 2 - 2.5mH motors is nice on 48V power. But the 3.6mH motors will be fine if you don't need maximum speed.



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    Default Re: Help with stepper motor/PSU specs

    Generally, to determine the voltage to use with your stepper take 32 times the square root of the inductance. So for 3.6mH that would be 60.72 volts and for the 6.8mH that would be 83.45 volts. I would the use the 270 oz-in motor and at least a 48 volt power supply. I'm using 381oz-in motors (KL23H2100-35-48) that are 2.8 mH on 48 volts and they never get more than very slightly warm. Mine calculated (32*SQRT(2.8)) = 53.55 volts so I am running just a few volts below that.

    You still have to consider the max voltage that the drives can handle and not exceed that.



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    Default Re: Help with stepper motor/PSU specs

    Read this

    https://www.geckodrive.com/support/s...or-basics.html

    Even though it is from Gecko, it applies across the board.



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    Default Re: Help with stepper motor/PSU specs

    So how do I determine exactly what current these motors will draw at higher voltages, and if my PSU is adequate?
    Most modern drives will never draw more than 2/3 of the rated current, or about 1.9 amps for your 2.8amp motor. So it should be fine supplying 2 amps/motor.

    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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Help with stepper motor/PSU specs

Help with stepper motor/PSU specs