Electrical problem with 3 step motors

Hi everyone,

I've made a 3 axis motion control system with nema23 step motors. Everything works just fine... except for one very frustrating problem : sometimes, while the whole system is wired and operational, one or more motors are slightly moving on their own - a few steps per seconds.
I think i found the source of the problem, but i'm not very good with electricity and it would be great to have a confirmation from an "electric guru" !
The 3 motor drivers are each powered via 6v/3A AC/DC wall plug. As the electrical transformers i use can deliver a max of 3A, i think that my problem comes from their instability at their limit. I also read in another forum that switch-mode power supplies are source of high frequency interferences...
Someone could confirm that ? Would the solution be to use a PC power alimentation ? Is there anything else i could do to have a "clean" electrical power for the stepper motor drivers ?

Many thanks for helping me

You need to post a link to the datasheet for the stepper motors.

What stepper motor drivers are you using?

I would expect your motors to perform much better with a 12v, 24v or 36v power supply. 6 volts seems very low.

Stepper Motor Basics

Many thanks for your reply :
The motor drivers are TB6560 like this one : http://www.ebay.fr/itm/3-A1-Axis-Controller-Stepper-Motor-carte-pilote-Pilotes-CNC-Router-TB6560-Simple-/151791767332?hash=item23577e8f24:g:zJcAAOxyeR9TJnEx
And the stepper motors are 57BYGH405A - you can have the tech spec here : http://www.prutchi.com/wp-content/uploads/2012/02/57BYGH405A.pdf
6V is not a lot, but it is almost twice what the motors really need (they need 3,6V). I've read that step motors can handle a higher voltage than needed if it is not too much above their specs.
I think that my problem comes from the AC/DC electrical transformer which works at his limits - he cannot deliver more than 6V/3A. Many thanks for helping

You should be running the TB6560 at 12 or 24V. Steppers are current driven not voltage
driven. You are limiting the motors to running very slow by not having decent voltage overhead.

A low step rate could be a symptom of interference on the step pin(s), so the question is
how have you wired things and is the cabling neat and short?

but it is almost twice what the motors really need (they need 3,6V).

It is not correct to say the motors "need 3.6v". What they need is 3 amps and the higher the voltage the better if you want torque at speed. The motor driver should be adjusted to limit the current to 3 amps to protect the motor.

I suspect the TB6560 drivers will struggle to provide 3 amps without overheating. It is usually a good idea to choose a driver with a bit of surplus capacity.


The 3.6V rating stems from the 1.2ohm internal resistance. So with a not-current-controlled driver you would be limiting to (3.6 / 1.2 =) 3 amps.

The 3.6V rating stems from the 1.2ohm internal resistance. So with a not-current-controlled driver you would be limiting to (3.6 / 1.2 =) 3 amps.

But they are not intended to be used like that.


A 1.2 ohm stepper is a low impedance motor - it is designed expressly for current control, not
voltage control. If the windings were 30 to 50 ohms then that would be a different story.

But they are not intended to be used like that.


But many years ago they were. Thus the use of the word "stems".

But many years ago they were. Thus the use of the word "stems".

I had assumed your use of the word stemmed from Ohm's law, not history :slight_smile:


Thanks for your answers,

I better understand the "current driven motor" caracteristics... reading your posts, I do think that i need to change my AC/DC for something more powerful : a pc power supply can deliver 12v with a lot amp, which sounds good ! I'll see if my problem is solved, and if not i'll try with motor drivers that can handle more than 3A.
And MarkT, I'll leave a schematic of the system very soon, but i now have a lot of work for the week end so i won't be able to leave it before monday. A lot of thanks to all you folks

I'm not sure if I'm talking nonsense now, but couldn't it also be the capacitors in your power supply giving off a little electricity after being turned off? I'm talking of the ones behind the rectifier which smooth out the voltage fluctuations. Could also be wrong....

Hi again,

Here is the schematic of the system :

I'm wondering if it is a good idea to wire all the ground together to the arduino.
And Smagel, if i understand correctly your post, changing the actual AC/DC for a PC power supply should also eliminate that possibility, don't you think ?
Again, thanks a lot for helping me

Yes, all grounds must be connected together, including the Arduino Gnd, so there is a common Gnd reference within the system.

OK, thanks for this confirmation CrossRoads

Good info on stepper motors regarding applied voltage.


Apparently the page on this site has disappeared....You can use the internet time machine to see the full article, but in short...

"Stepper motor drive bus voltages are a tool that can be used to tune the performance of your system. By increasing the bus voltage the driver runs on, the speed and torque and power output of the motor all increase. Because of these benefits, stepper motors are operated with bipolar ‘chopper’ drives at voltages many times their nameplate voltages. Generally, 12 [V] is the smallest voltage used to drive actuator motors, with higher voltages at 24 [V], 48 [V] and even 80[V] being used for motion control systems. A good rule of thumb is to use between 10 and 24 times the motor’s nameplate voltage for the system bus voltage."

Mr. Geckodrive says the maximum voltage should be either 25 times the nameplate voltage or 32 * sqrt(inductance in mh). He doesn't provide any solid foundation for it but rather states that it's based on empirical evidence.

The deciding factor appears to be the iron losses of stepper motors causing heating. That effect is very small at low voltages and then increases exponentially with higher voltages. Past a certain voltage all you do is generate a lot of heat.

Iron losses are solely due to rate of change of magnetization, which is due to current changes. (*)

The voltage allows a greater rate of current change - basically iron losses increase with frequency
and amplitude, and are inherent in making a motor go faster, whatever voltage you use.

Higher voltages mean higher chopper switching frequencies though, which leads to more losses
in the chopper circuit, which may be important too. Again that is fundamental to getting faster
motor speeds.

Iron losses do increase exponentially with anything.

(*) Actually its a complex function of magnetic history, since some magnetization energy returns to
the circuit as the current falls, some generates heat directly, and some causes eddy currents which
then generate heat.


Thanks Zipfactor : the link is very interesting, and i now realize that my motors do not have enough voltage to run properly. BUT, as the author said, i should use about 10 to 24 times the nameplate's voltage which means 36v to 86,4v... far above what a PC power supply can do. So i'm not sure anymore to use a pc power supply for my system : it would be great if someone could give an advice of a cheap power supply that could handle 36-80V and 20A (i actually need 9A for the three motors, but i'd like to control six in the future).
And again, a lot of thanks for your posts : i'm beginning to much better understand the way step motors work

The higher the supply voltage the lower the current you need for slow motion.

Full speed under load is when it will draw significantly more current, but generally the
supply gives less current than the motors take from the chopper.

I got this supply recently from Amazon here in the UK:

For more motors add more supplies perhaps?