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I am using Oriental's PK-243-03A stepper motor in bipolar series configuration. The driver I am using is TI's DRV8825. I want to measure my motor's current in order to plot a Speed - Current graph. I have figured out a way to measure speed using photo - interrupter, but I am a little confused on how I should measure the motor's current. I have a couple of questions.

The driver IC I am using has an Isense pin in it which uses an Rsense resistor to set current threshold value for my motor, maybe I can measure the current from there somehow, but how?

Or can I attach an ammeter in series with the VMx pin of the driver and measure current?

Is there any tested or proven method for measuring current? I can really use the help.

Thanks in advance!

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2 Answers 2

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When current goes through a resistor, a voltage drop appear across its terminal
So if you measure the voltage across the sense resistor RisenA and RisenB, you get the current through each winding
You can also use a scope to see its form.

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  • \$\begingroup\$ Yes I can measure current with sense resistor but how will I get the total current drawn by the motor to plot the graph? or is it okay to plot Speed graph against single winding current? \$\endgroup\$
    – alexhilton
    Jan 9, 2015 at 11:52
  • \$\begingroup\$ If you have a scope, you can just sum the 2 waveforms you're getting on the screen, and that should represent the actual current consumption of the motor. \$\endgroup\$
    – HatimB
    Jan 9, 2015 at 11:58
  • \$\begingroup\$ I inserted a ammeter in series with the winding and saw the relationship of speed and current, and it worked! \$\endgroup\$
    – alexhilton
    Jan 13, 2015 at 8:32
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Its not really a answer. But hope it helps a bit! Just measure total current consumption. This driver have current limitation? Most cases you want to go with higher voltage and control only current flow. Check terms like "chopper" "pwm" "current limit", if you use driver with chopper its hard to measure current. Check also term "true RMS".

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  • \$\begingroup\$ I was thinking the same to measure the total current consumption but how? If you see the IC is capable of driving 2.5A of current from each output. And yes it does use a chopper \$\endgroup\$
    – alexhilton
    Jan 9, 2015 at 12:42

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