# determine necessary current to drive a stepper motor?

I am trying to drive a stepper motor. It is a 12V unipolar motor. But it is not moving. I tried with L293D , ULN2003 etc. I think it is not getting sufficient current. But how do I determine how much current is necessary, so that I can chose a driver IC? In the datasheet there is no current mentioned.

• My question might be naive.. have you driven any other stepper motor earlier? – Umar Jun 27 '15 at 7:27
• Model specification has the phase resistance as 300 Ohms. Current should be 12/300 = 40 mA per phase and zero until phase is changed.. Correct me if i am wrong. If possible, share the wiring diagram – Umar Jun 27 '15 at 7:54
• No,this is my first time with a stepper motor. – Nafis Jun 27 '15 at 12:44
• learn.adafruit.com/all-about-stepper-motors/… Doesn't take much time. Stepper motor is a must in so many robotics and motored drives. Learn more about it. Driving motor is easy. – Umar Jun 27 '15 at 16:52

This type of stepper does not use much current, in the datasheet, you can see that

Stepper has gear reduction 1:64

Step angle $${360\text{º}\over64\text{º steps}} = 5.625º\text{ pr step}$$

which is full-step.

Resistance per phase is

$${12\text{V}\over300\text{Ω}} = 40\text{mA}$$

If you need more current than the circuit can provide, then you must use a power driver like this.

Moving a stepper may be not as trivial as it seems. Do you hear it trying make steps? Most of the beginners drive it without motion profile, skipping the acceleration, so the motor sometimes doesn't follow and only make noise.

Also the motor is bipolar. Are you sure, you are driving the steps correctly? Reminder: you have four steps:

Phase A: I, phase B: I Phase A: I, phase B: - I Phase A: - I, phase B: - I Phase A: - I, phase B: I

This is the order of currents.

Of course, it is expected that the current is controlled, otherwise when the motor is not moving, it may rise and burn things or dip the power supply.