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  1. #1
    ian's Avatar
    Lives in London, United Kingdom. Last Activity: 20 Hours Ago Has been a member for 0-1 years. Has a total post count of 11.
    Hi

    I need to source a PSU and am confused about the size calculations as I have limited experience.

    I intend to run 4 x Nema 24 closed loop motors, 4Nm, 5.0A, 2.5mH inductance. I want to run these at best performance and understand that the inductance als needs to be considers. So I calculate

    1. Square root of 2.6 x 32 = 51V, so at least a 48V PSU

    AND a second recommended calculation is

    2. P= 4 x 5 x 48 x 1.2 = 1 152W

    But it seems most 48V PSU's deliver 350 - 400W at 7-8A.

    1. Since the PSU's are rated at 7A, do I need 1 x PSU per stepper motor since more than 1 motor will exceed the A rating?
    2. Since the PSU's are rated 400W, do I need 1 x PSU per stepper motor since more than 1 motor will exceed the W rating?

    Knowledge, experience and constructive critique welcomed!

    Ian

  2. #2
    Before we get into that which drives and closed loop system are you thinking to use.?
    -use common sense, if you lack it, there is no software to help that.

  3. #3
    ian's Avatar
    Lives in London, United Kingdom. Last Activity: 20 Hours Ago Has been a member for 0-1 years. Has a total post count of 11.
    Hi

    these ones from steppersonline:

    https://www.omc-stepperonline.com/cl...nd-driver.html

  4. #4
    Ok well then the limiting factor now is the 50vdc Max drive limit. For safety you really need to leave a 10% safety margin for back Emf when the mootrs are slowing down and effectively turn into dynamos and send voltage back to the drives etc.

    So 45Vdc is the Max you can run these motors at safely. If you try to push more then you risk the chance of blowing the drives up.

    What machine is this going on.?
    -use common sense, if you lack it, there is no software to help that.

  5. #5
    ian's Avatar
    Lives in London, United Kingdom. Last Activity: 20 Hours Ago Has been a member for 0-1 years. Has a total post count of 11.
    Hi Jazz CNC

    I've have build a first version as a proof of concept (see picture attached), but am now starting a new "better" build and am looking at what the ideal PSU should be so that I can buy the right one (or multiples if needed).

    The aim is to build a bench-top CNC router, able to cut a lot of engineering plastics of up to 600mm x 600mm x 40mm with reliable precision and accuracy of 0.01mm at the most optimale speed (which seems to be 3500mm/min+) and at 3200 resolution. The machine will be used to make prototype enclosures for GPS trackers for cattle and sheep and accuracy is important due to the products requirements and to achieve good surface finishes and potentially also cut PCB's. Ideally the machine will be housed in a sound/dust enclosure as it will be in my office and I will need easy access to it to build prototypes and keep an eye on small production batches, making 100's off enclosures weekly, so the machine will operate 4 hours per day and must be reliable. I will also cut some aluminium plates for making prototype moulds.

    I'm not yet sure how achievable and realistic the above is as the budget is also somewhat limited, but I intend to build incrementally from the basics (solid frame and linear motion) and add more automation and features later on (assuming I can define a good end-design in the beginning and build towards it).

    So far I have the following items for my next iteration:

    X & Y
    3 x 800mm 1605 ballscrews, C7
    3 x pairs 800mm Hiwin 15mm rails and 2 HGR15CA carriages per rail

    Z
    1 x 250mm 1605 ballscrews, C7
    1 x pairs 300mm Hiwin 15mm rails and 2 HGR15CA carriages per rail

    4 x Nema 23 motors, 4Nm (want to change to closed loop steppers and drivers as step errors can ruin expensive components)

    40mmx80mm extrusions for the frame (need to change these as they are not rigid enough)

    Blackbox controller (from Openbuilds), 24v power supply, limit switches (ALL of this needs replacement with better components - these were only for my proof of concept machine build)

    I'm currently working on the designs for the plates which is likely to be 15mm aluminium.

    What would the ideal PSU specs be for such a machine and the closed loop motors?
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  6. #6
    Well like I say with those 50Vdc drives then you really don't want to run much above 45Vdc, I certainly wouldn't run them at 48vdc because it's like playing Russian roulette.

    I would build a PSU using a toroidal transformer rated at 500Va with 30V secondary outputs wired in parallel. This will give you approx 43Vdc and 16A but usually, the incoming mains fluctuates anywhere between 230Vac and 250Vac so in use you'll probably end up around 45Vdc.
    If you know your incoming voltage is stable and 230vac then you could go with a 32Vac transformer which will give you 45Vdc. Personally I wouldn't because a few less volts won't make a big difference to the speed but certainly will blow a drive up.

    Now regards the speed and running at 3200 resolution, by which I presume you mean micro-stepping.? Then first off I need to say that Micro stepping shouldn't be classed as resolution as that is a function of the ball screw and micro-stepping is more intended for smoother running of the motors. However, because of how steppers work there is a limit to what is useful and usable. Most steppers can't resolve down to high micro stepping levels and 3200 is about at the Max that is useful.
    Now the side effects of running at this level of MS are lower torque and much higher demand on the controller. For instance, you'll double the amount of pulse frequency required for 3200 than 1600 but have less torque with very little gain in motor smoothness. If your motion controller is limited to say 25Khz then this will half the velocity, so it's only worth running at high MS-like 3200 if you have an excess frequency in the controller.
    1600 Ms is more than enough for any stepper system and doesn't tax the controller.

    Now with those 2 phase closed-loop steppers and 45Vdc you'll get around 900Rpm that is usable and will max out around 1200-1300Rpm before stalling.
    So with 5mm pitch and 900rpm then provided your axis are not binding or sticky and the gantry isn't silly heavy then your Max velocity will be around 4500mm/min and you may push it just above 5000mm/min.
    A realistic MAX cutting velocity of 4000mm/min is about what I would estimate with those motors/pitch and voltage.
    -use common sense, if you lack it, there is no software to help that.

  7. #7
    What about buying them in seperates instead of kitted and getting the 20-80VAC/30-110VDC drivers instead?
    https://www.omc-stepperonline.com/cl...20100%20VDC%5D
    https://www.omc-stepperonline.com/cl...38%2C651.54%5D

    Then drop a 500va 30-35v AC toroidal straight into them?

    Costs a little more but.
    You'll then safely be able to use the voltage you want to run and have the headroom not to worry about the back emf.
    Prob get the setting unit to limit the current.
    Just a thought.

  8. #8
    Quote Originally Posted by dazp1976 View Post
    What about buying them in seperates instead of kitted and getting the 20-80VAC/30-110VDC drivers instead?
    https://www.omc-stepperonline.com/cl...20100%20VDC%5D
    https://www.omc-stepperonline.com/cl...38%2C651.54%5D

    Then drop a 500va 30-35v AC toroidal straight into them?

    Costs a little more but.
    You'll then safely be able to use the voltage you want to run and have the headroom not to worry about the back emf.
    Prob get the setting unit to limit the current.
    Just a thought.
    I deliberately didn't suggest any alternatives so as not to muddy the waters and because you said budget was a factor. However now it's been suggested then here's what I would go for.
    These are strong motors at 5.5nm, the drives accept AC or DC voltage, us AC and you only need a toridal transformer, feed them 60-65vac and they spin like a spinny thing spinning.!
    https://www.aliexpress.com/item/3279...231e3421DuPQOO

    The transformer will need to change though, 30V 500Va wired in series will only give 8.3A so 625Va will be a better choice with the secondarys wired in series to give 60Vac with 10A.


    Now here's another twist.!!
    If you don't want to go with the bigger motors which from the sounds of it you don't need then consider using 3 phase closed-loop rather than those 2 phase you have been looking at.
    3 phase motors are stronger and smoother, they also spin a little faster. Personally I wouldn't use small 2 phase closed loop motors because as you'll see you can get 3phase for the same money. The 1.2deg step angle makes them much smoother and the extra phase makes them stronger higher up the rpm range, so while they are no stronger in total Nm rating and use the same 50Vdc Max limit on the drives they do have a stronger torque curve which matters if your wanting to spin fast as they have more push high up.

    https://www.aliexpress.com/item/3260...ba33761fmpzbBE
    -use common sense, if you lack it, there is no software to help that.

  9. #9
    Generally with normal 4 axis nema23/24 'kits' around 3.5 - 4nm holding you get 2 supplies of 350w each.
    So that is 1 supply per 2 drivers/motors.
    With nema34's you get 1 supply per axis.

    This 48v 600w supply here says it will drive 4 of there 8 wire motors when in parallel. I can't see why one of these wouldn't be fine for yours:
    https://www.cnc4you.co.uk/Stepper-Mo.../60HS111-4204F
    However if it seems a bit close to max they also do a 48v 480w version which you could opt for, buy 2 of them and put 1 supply per 2 motors. (Or go all out and just get 2 of the 600's. they'll prob run at half power and last for life!)
    https://www.cnc4you.co.uk/Breakout-B...U-48Volt-10Amp

    Their similar motors they suggest the supplies for are 4A and 3mh inductance in parallel and 12mh in series. Series would require more power.
    https://www.cnc4you.co.uk/Breakout-B...U-48Volt-12Amp
    I have these exact above motors working on 60v. (I have the 24-80v type drivers)

    I'm considering having a crack at building a toroidal supply to output around 55vdc so I can ditch my meanwells and make some space in my control box.

  10. #10
    Quote Originally Posted by dazp1976 View Post
    Generally with normal 4 axis nema23/24 'kits' around 3.5 - 4nm holding you get 2 supplies of 350w each.
    So that is 1 supply per 2 drivers/motors.
    With nema34's you get 1 supply per axis.

    This 48v 600w supply here says it will drive 4 of there 8 wire motors when in parallel. I can't see why one of these wouldn't be fine for yours:
    https://www.cnc4you.co.uk/Stepper-Mo.../60HS111-4204F
    However if it seems a bit close to max they also do a 48v 480w version which you could opt for, buy 2 of them and put 1 supply per 2 motors. (Or go all out and just get 2 of the 600's. they'll prob run at half power and last for life!)
    https://www.cnc4you.co.uk/Breakout-B...U-48Volt-10Amp

    Their similar motors they suggest the supplies for are 4A and 3mh inductance in parallel and 12mh in series. Series would require more power.
    https://www.cnc4you.co.uk/Breakout-B...U-48Volt-12Amp
    I have these exact above motors working on 60v. (I have the 24-80v type drivers)

    I'm considering having a crack at building a toroidal supply to output around 55vdc so I can ditch my meanwells and make some space in my control box.
    I'll say it again so if the OP decides to ignore the advise and go with 48V he cannot say he wasn't warned.!!! . . . . . 48Vdc is too close to the drives Max rating and it's only a matter of time before it gets damaged.

    Why anyone would fit a PSU on each drive is beyond me.??
    -use common sense, if you lack it, there is no software to help that.

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