Stepper motor in series power in one bu CNC shield

Hi Everyone,

Two stepper motors in series and they are plug by one pin of output of each x, y, z and they will give enough power for two stepper motors?

one stepper motor is 1.7A and DRV8825 Current Limit Vref is about 0.75A, but if two stepper motor and then need 1.5A output for two of them?

Regard

Chris Van Grewden

one stepper motor is 1.7A and DRV8825 Current Limit Vref is about 0.75V, but if two stepper motor and then need 1.5A output for two of them?

No…If you wire the two motors in series then the current flowing from the driver flows through both motors. As there are now two sets of two coils the stepper driver has twice the coil resistance to overcome to push 1.7Amps through the pairs of coils so automagically adjusts the voltage at it’s terminals to push that current through the two coils.

Ohm’s law states V=IR
As each motors coil is about 2.4ohms and you want 1.7amps flowing through it then you need 3.78volts to do it, if you double the resistance (by adding another coil in series) then you will need twice the voltage to push it 'ie (2.4x2)x1.7=7.56v. Now as you are supplying the drivers with at least 12v you have the headroom to run the motors in series…things start getting a bit tricky if you are using motors that have a maximum current of 2 Amps and a coil resistance of 3.5ohms because you need at least 14v to push that current around the coils so have to use a higher voltage power supply…usually 24v.

If you wire the motors in parallel then you would need 3.4Amps coming from the driver as the current is split between the coils and each coil would want approx half each.

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I need 3.78 volts to through stepper motor, but my stepper motor has limit volt is 2.7 V

Quick Wantai 42BYGHM809 stepper motor specification:

  • Voltage rating: 2.7 V
  • Current rating: 1.68 A
  • Resistance: 1.6 Ω per coil

I have 24v 6.5A power supply.

I need 5.4V for two stepper motors in series in each X and Y

I checked internet to help me to adjust reference voltage for stepper motor, they doing VREF for single stepper motor but what about two stepper motor?

Check link here: https://cobcnc.com/adding-a-cnc-shield-and-tuning-drv8825-drivers/

Before you get too bogged down in the electrical engineering calculations, remember that there are literally hundreds of MPCNC machines out there running two stepper motors off of one driver, wired in series, with the driver set as if it were for one motor (likely around 0.6, or very slightly higher, Vref for your DRV8825 and those motors). They push plenty of current for the tasks we set them to. I would start from there, and only revisit those numbers if you start skipping steps on a regular basis. You’ll likely run into thermal shutdown issues before you skip steps, though. At least, that’s my take from everything I’ve seen.

3 Likes

Thank you very much for help.

Hi
Now I understand how power output work from single pins for two series stepper motors,

I realized those two stepper motor draw more amps.

I played with two stepper motors in series to test with power and they are running prefects :slight_smile:

Thank you very for explain about power out for two stepper motors @kvcummins and @dart1280