# How to find stepper motor's rated current to set current limit?

I am trying to set the current limit on a NEMA 17 stepper motor. I found a tutorial but it's asking about the current rating. From my stepper motor datasheet, the only information related to current is the following: Rated Current (Amps/Phase) = 1.68 A. In the online tutorial that i'm following, this is the example given for their stepper motor: NEMA 17 200steps/rev, 12V 350mA. So, i'm quite sure that the current rating that is being asked is not 1.68 A. Maybe i need to calculate the current rating??

Edit: Here are the more complete specs for my hybrid stepper motor, model: MT-1703HS168A

Rated Current (Amps/Phase): 1.68

Holding Torque (kg.cm): 4.4

Resistance (Ohms/Phase): 1.65

Inductance (mH/Phase): 3.6

Inertia (g.cm2): 54

Detent Torque (g.cm): 150

Weight (kg): 0.28

Recommended voltage: 12 - 24 V

No, you have the right rating, it is just that you have a much better motor than in the tutorial.

The motor in the tutorial is a high voltage, low current one. The problem with this is that as a result it has a high inductance, and meaning that it take a while for current to rise to the rated value after each step, which means that the torque when stepping rapidly will be much less than the rated torque. To overcome that, a higher voltage driver (say 36 volts) would be needed with a chopping current regulator.

Your motor with a nameplate spec of 1.68 Amp per phase will be built for a lower steady-state voltage (probably around 3-4 volts, though that is only a guess), and will have a lower inductance. As a result, it will probably perform well when used with a chopping current regulator powered from 12v.

Of course it is possible your current driver is not rated to provide that much current.

Decent 3d printer kits for example may supply low voltage high current motors for the X and Y axis and extruder; but they often cheap out and supply a high voltage low current motor for a screw-drive Z axis, figuring that the Z axis does not need to produce a lot of torque (or if direct drive, does not really need to move very quickly). A yet better kit might use decent motors there, too.

• I updated my first post with the rest of the specs for my stepper motor. I am using A4988 stepper driver and i'm following this tutorial lastminuteengineers.com/… and the section titled "Current limiting". But i'm worried and very concerned (i already damaged two A4988's) about setting the current all the way up from the suggested 350 mA to 1.68 A?! Isn't it going to cause any damage? In my previous setup, i omitted the decoupling capacitor at the stepper driver's VMOT and GND inputs and it killed my Arduino together the A4988. :( Commented Apr 30, 2019 at 22:22
• Is not having the decoupling capacitor the only possibile reason why all the components were damaged? I had the current limit set to 0.6 A. Commented Apr 30, 2019 at 22:24
• I found this excellent tutorial video from Pololu: youtube.com/watch?v=89BHS9hfSUk I hope this proves useful to anyone else struggling to fully understand how to set the current limit. Commented Apr 30, 2019 at 22:42
• @DryRun I'm pretty sure you'll have figured out by now that the A4988 is rated for 2A, and so should be fine at 1.68 provided that you give it an opportunity to cool itself a little (don't pack wires tightly around it, maybe even give it some forced air). Commented Feb 25, 2021 at 19:44
• @DryRun it's very highly unlikely that the removal of the decoupling capacitor damaged anything. That capacitor is there only to stabilize VCC against very-short-duration voltage sags. The A4988 should be dealing internally with any inductive slapback. Why would you remove it, though? Commented Feb 25, 2021 at 19:47