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DRV8828EVM / waveform of motor current

K.Yaita
Guru 29690 points
Hi team,
 
My customer is evaluating DRV8828EVM+103H7823-57XE40(stepping motor:SANYO DENKI).
http://www.q-tech.hu/pdf/SanyoDenki/2%20phase/60H%20-2ph_F2-SteppingMotor.pdf
 
He pointed out that the motor current decreases with increasing the value of "Desired Speed PPS" in Full Step as EXCEL attatched.
Is this waveform normal for Full Step?
 
He set VREF=2.5V / sense resistor=200mΩ(full-scale chopping current=2.5A) and the GUI setting is the following.

My customer has no experience to evaluate stepping motor in past time, so your advice would be helpful.
 
Best Regards,
Yaita / Japan disty
  • 0
    TI__Mastermind 20985 points

    Yaita-san, yes this is normal.  When more than 300 PPS is used, the current can't reach the peak level before the next step occurs, so the average current is less.

    Best regards,
    RE

  • 0 in reply to RE
    Guru 29690 points
    RE-san,
     
    Thank you for your precious reply.
    Does it mean we have to set less than 300 PPS(Desired Speed) for this motor?
    Is there any concern to set more than 300 PPS?
     
    Best Regards,
    Yaita
  • 0 in reply to K.Yaita
    TI__Mastermind 20985 points

    You can run faster than 300 PPS, as long as the motor spinning behavior is acceptable and it produces enough torque.

    If you can increase the VM voltage, that will help current change faster for better performance.  Or, if you need less torque (current), you could regulate current to a lower level and have a better-looking current waveform.

    Best regards,
    RE

  • 0 in reply to RE
    Guru 29690 points
    RE-san,
     
    Thank you for your quick support.
    I understood.
     
    Best Regards,
    Yaita
  • 0 in reply to K.Yaita
    Guru 29690 points
    RE-san,
     
    I need your advice once again.
    My customer is evaluating DRV8828EVM with the stepping motor that characteristic of pulse rate-torque is the following.
     
     
    According to this motor characteristic, I believe 1kPPS is well operable in full step.
    However, the motor couldn't rotate normally if "Desired Speed PPS" of DRV8828EVM is more than 700PPS even no load condition.
    The setting of GUI is same as described above and VM is 24V.
     
    Is there any concern about this issue?
    (Is this issue caused by setteing of DRV8828EVM?)
    Your help would be really appreciated.
     
    Best Regards,
    Yaita
  • 0 in reply to K.Yaita
    TI__Mastermind 20985 points

    Yaita-san, good question.

    I looked up the datasheet for 103H7823-57, and found this: http://www.q-tech.hu/pdf/SanyoDenki/2%20phase/60H%20-2ph_F2-SteppingMotor.pdf  It shows the same torque curve, but below the graph it says "AC100V, operating current: 4A/phase".  So we see conflicting info on this motor's characteristics.



    The waveforms you sent show that it took 2ms for the current to rise from 0A to 2.5A.  It should be 4 times faster (0.5ms) if 100V is applied.

    Have you tried using other decay modes?  You could also try measuring both phases at the same time to make sure they are in sync correctly.

    Best regards,
    RE