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  1. #1
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    Problem with cranking up the current for steppers

    Hi all

    I have this setup

    PoKeys57CNC
    3 * NEMA 23 - 0.7Nm - 1/4" shaft (1=Z, 2=Y)
    NEMA 23 - 1.3Nm - 1/4" shaft (X)
    Power Supply - 24V 10A (Noname)
    Stepper Driver 2.5A - PoStep25-32

    My problem is when I crank the current up for the Y-axis. RIght now my settings is 1Amp for X-axis, 0,5A for each stepper on the Y-axis and 0,5A for the Z-axis. I would like to run the two steppers on the Y-axis with more current, because I have understood that this will give them more torque, and right now (with only 0,5A each) they do not have power enough to run to the bottom of the Y-axis, it is like my dragchain is simple too heavy for it to drag it (hope it makes sense?).

    The stepper drivers I am using have a jumper to switch current for the steppers (0,5; 1; 1,5; 2; 2,5), when I just try to increase each Y-axis motor to 1A, a relay shots in when trying to power on the setup, and it wont start.

    Does anybody have suggestions for some troubleshooting I can do, or have anybody tried similar things?

    Thank you.

    (hope this is the right place to post, else please let me know)

  2. #2
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    Re: Problem with cranking up the current for steppers

    What size is your machine?
    Retired Master Electrician, HVAC/R Commercial. FLA Saturn 2 4x4 CNC Router

  3. #3
    Community Moderator ger21's Avatar
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    Re: Problem with cranking up the current for steppers

    What are the current ratings of the motors? If you exceed the ratings, you'll damage the motors.

    Where is this relay connected?
    Gerry

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

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

    JointCAM - CNC Dovetails & Box Joints
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    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

  4. #4
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    Re: Problem with cranking up the current for steppers

    Quote Originally Posted by wmgeorge View Post
    What size is your machine?
    The size is 1000m * 750mm

    Quote Originally Posted by ger21 View Post
    What are the current ratings of the motors? If you exceed the ratings, you'll damage the motors.

    Where is this relay connected?
    Up to 2A for the three small motors and up to 2.8A for the large motor

    I have not connected any relays to the setup, I think it must be the PSU? But I really don't know. It can also be that it is not a relay, but it just act like one. When I power up the setup, it sounds like a click and the setup shots down. The LED on BOB is only on for half a second or less.

  5. #5
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    Re: Problem with cranking up the current for steppers

    I am guessing your “no name” power supply is not up to the load and it’s shutting down. Is there a voltage rating on the motors?

  6. #6
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    Re: Problem with cranking up the current for steppers

    Quote Originally Posted by wmgeorge View Post
    I am guessing your “no name” power supply is not up to the load and it’s shutting down. Is there a voltage rating on the motors?
    Ok so I should try to switch PSU to maybe a 36V? This is what info I have about the motors

    https://ibb.co/7CycQ6r

  7. #7
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    Re: Problem with cranking up the current for steppers

    Quote Originally Posted by tangi View Post
    Ok so I should try to switch PSU to maybe a 36V? This is what info I have about the motors

    https://ibb.co/7CycQ6r
    I guess I am not smart enough to figure the voltage out but if your limiting the amps I don't see how it could damage the motors using a 36 volts. But you need to look at the amp rating of the PS and get one designed for CNC work. It may be a DC power supply but your stepper drivers are outputting pulses. Here is a screen shot of a stepper motor being operated at different voltages. FYI.
    Retired Master Electrician, HVAC/R Commercial. FLA Saturn 2 4x4 CNC Router

  8. #8
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    Re: Problem with cranking up the current for steppers

    Quote Originally Posted by wmgeorge View Post
    I guess I am not smart enough to figure the voltage out but if your limiting the amps I don't see how it could damage the motors using a 36 volts. But you need to look at the amp rating of the PS and get one designed for CNC work. It may be a DC power supply but your stepper drivers are outputting pulses. Here is a screen shot of a stepper motor being operated at different voltages. FYI.
    Thank you very much for the chart wmgeorge. I am not smart enough neither to figure it out. The Y-axis is set to a very low velocity in Mach3 to have some torque and is running as I remember 1/8 steps. I tried back and forth, and this was the best results as I could get. But sadly I cannot use, I think 1/3 of the possible machine area of the CNC, because the Y-axis isn't strong enough to run to the bottom of the axis.

  9. #9
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    Re: Problem with cranking up the current for steppers

    I have been searching a bit more. I thought that maybe my wiring could have something to do with it. My drivers are wired in parallel and not serial, can this maybe have an effect that causes the problem? It seems that a lot of people are wiring the power in serial mode between the stepper drivers.

  10. #10
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    Re: Problem with cranking up the current for steppers

    Quote Originally Posted by wmgeorge View Post
    I guess I am not smart enough to figure the voltage out but if your limiting the amps I don't see how it could damage the motors using a 36 volts. But you need to look at the amp rating of the PS and get one designed for CNC work. It may be a DC power supply but your stepper drivers are outputting pulses. Here is a screen shot of a stepper motor being operated at different voltages. FYI.
    36v shouldn't damage the steppers, but it can certainly damage the drivers. Looks like the PoStep25-32 are only rated for up to 30v.

  11. #11
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    Re: Problem with cranking up the current for steppers

    Yes, it does say on the driver printboard max 40V, but yeah in the manual 30V. But I am thinking of changing the PSU to 36V, but then turn it down to maybe around 28V. Does that sound as a good idea?

  12. #12
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    Re: Problem with cranking up the current for steppers

    Your drivers are undersized re voltage for NEMA23
    24 volts is not enough for good performance. I've been there and done that.
    Somewhere on Gecko's site I read 2 things:
    1. If you double the voltage you quadruple the torque
    2. The total amperage draw of your steppers can safely exceed your power supply output by 40%

    I drive my NEMA 23's with a 48 Volt power supply with drivers that are good for 50 volts.
    With 4 x 2.5 amp steppers, you will be fine with a 7 amp 48v power supply.
    You will never get satisfactory performance at 24 volts. Bite the bullet and upgrade and you will be amazed at what the difference you will get from your machine.
    Rod Webster
    www.vehiclemods.net.au

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