# Current Settings for Motor Controller



## devils4ever (Feb 15, 2020)

Okay, I'm finally ready to finish wiring up my PM25 mill with my CNC conversion. I copied what shooter123456 used as far as motor and motor controllers. I'm having trouble determining how to set the current on the motor controllers.

I have two NEMA 23 motors (Stepperonline: 23HS33-4008S) rated at 400 oz-in for X and Y and a NEMA 34 motor (Stepperonline:34HS38-3008S) rated at 1001 oz-in for Z.

Based on discussions with shooter123456, I'm wiring them as Bi-Polar Parallel to increase response. In this configuration, the Amps/phase are 5.66 for the NEMA 23 and 4.24 for the NEMA 34. (Why does the stronger motor use less current?)

My controllers are DM542T for the NEMA 23 motors and DM860T for the NEMA 34 motor.

The settings for the DM542T controller are:
Peak    RMS
-----  -----
1.00A  0.71A
1.46A  1.04A
1.91A  1.36A
2.37A  1.69A
2.84A  2.03A
3.31A  2.36A
3.76A  2.69A
4.20A  3.00A

For the DM860T:
REF    Peak
-----  -----
2.00A  2.40A
2.57A  3.08A
3.14A  3.77A
3.71A  4.45A
4.28A  5.14A
4.86A  5.83A
5.43A  6.52A
6.00A  7.20A

How should I set these? It seems the DM542T controller can't provide enough current?

Thanks for all input.


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## RJSakowski (Feb 15, 2020)

I'm no expert on stepper motors but here is my take.  Stepper motors are normally driven from a power supply  of mich higher voltage than the native voltage of the motor.  This is to increase available torque.  The controller regulates the drive current to prevent motor overheating and burnout.  Too much current, and the motor runs hot and is noisier.  Too little current and the motor isn't delivering the required torque.

As to the discrepancy between the  NEMA 23 and NEMA 34 motors, the NEMA 34 motor has a larger diameter rotor so it is able to generate more torque for a given current.  This will be at the expense of high speed response.

I just wrapped up an electronic lead screw project on my lathe using a NEMA 24 motor and driver from StepperOnline.  The driver was rated at 48 volts, max.  I elected for a 42 volt switching power supply to maximize response. My current is set at the maximum rating for the motor, 5.8 amps/phase.  A lower current setting will work but at the expense of lower torque.  So far, no issues.   

FWIW, I measured the thrust that the carriage was able to supply at around 110 lbs.  This with the stepper turning at around 570 rpm, a lead screw pitch of 12 tpi., and 2:1 gearing. This would be equivalent to 24 ipm.


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## devils4ever (Feb 15, 2020)

Agreed. I'm using a 48V 7.3A power supply. One for the NEMA 34 and one shared between the two NEMA 23's.

That makes sense. The NEMA 34 is *much *heavier and larger.

Well, I'm not sure the DM542T controller can deliver the needed current. 

I just rigged up everything to try it and I got another issue. One of the 48V power supplies doesn't always come on. If I cycle power enough times, it might come on.


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