Power Supply Sizing



  • I am sizing the required power supply for a setup having just purchased a Duet 3. I am looking to run 6 Nema 23 (1.3Nm, 2.8A, 1Ohm Resistance) steppers synchronously at 24V. My understanding is that the motors will require ~30W each, so about a 200W supply, but would appreciate any advice. I will be running the motors at a max of 200rpm. Apologies, Im sure this topic is answered previously on the forum but I have not been able to find it. Thanks in advance!





  • Hi, I did read this, unfortunately the numbers I get out from the rated current squared and the current x voltage on the motors Ive got are very different (which I realise is just the suppliers mistake), so I wanted to get a picture of what would typically be expected for these sized motors before committing to an under/over sized supply.



  • @tomlj

    I would that the psu for motors only is very low , 100 watts or less .

    Most of the time why you need a large psu is due to the heated bed.


  • Moderator

    Well those are quite large motors. Based on this:

    Stepper motors: at full rated current, the power needed for each motor is its rated current times its rated voltage (if no rated voltage is specified, use the square of the rated current times the phase resistance). This is the power at standstill. To allow for driver losses and the extra power needed to create acceleration, add 50%. Multiply by the number of stepper motors.

    Now is the rated voltage of the motor 24v or is that just your PSU voltage?

    Do you have a spec sheet for the motors?



  • Thanks for your responses, I plan to use a 24V power supply as it is compatible with some external (low power) peripherals I need to use. The motors as far as I can tell are rated 12V, but the listing (Amazon) doesnt offer a great deal of detail so I cant be certain. The details listed are
    Step Angle 1.8°
    Rated Current 2.8A
    Holding Torque 1.3Nm
    Phase Resistance 1.0Ohm
    Phase Inductance 2.1mH
    Rotor Inertia 460g.cm²
    Shaft Diameter: 6.35mm
    Motor Body Length 76mm


  • Moderator

    Can you share the listing? Do they have a model number?

    Consider shopping here instead so you can be sure of what you're getting.

    https://www.omc-stepperonline.com/



  • I shall take note of that! The next day delivery was too tempting at the time. Here is the listing for the motors Ive purchased:

    https://www.amazon.co.uk/gp/product/B07QN1YX98/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1



  • @Phaedrux said in Power Supply Sizing:

    Can you share the listing? Do they have a model number?

    Consider shopping here instead so you can be sure of what you're getting.

    https://www.omc-stepperonline.com/

    I might be blind, but they don't publish rated voltage? Seems odd but I may have missed it. Plenty of other specs though.

    (2.8A)^2 * 1Ohm *1.5(scaling)= 11.8W
    Looking at some roughly equivalent Oriental Motor specs, I'd guess they're rated for about 3V or so
    2.8A * 3V = 8.4W

    The Nema23s I'm using are rated at 1.6V and .57ohm, at 2.8A/phase.
    (2.8A)^2 * .57Ohm *1.5(scaling) = 6.7W
    2.8A * 1.6V = 4.48W

    I'd say the two methods (Voltage vs. Resistance) get pretty close (remove the scaling factor and they are actually nearly the same). Going bigger never hurt anything but your wallet! 🙂

    Don't forget to add in fans, heaters etc.


  • Moderator

    Well at least we know they are quiet.

    9def1b1b-dba0-49bc-86fd-dd36e0c6ac36-image.png


  • Moderator

    So your estimate of 30W each motor looks a bit overboard based on the good guesstimates from @sebkritikel



  • That's brilliant, thanks again for your help. I found the voltage from digging around the model number but certainly seems it wasn't for the right thing. I'll get a smaller power supply than planned and be very grateful for saving a few quid.


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