All I was writing is what to many is not obvious that any modern stepper motor control system you automátically have the PWM limiting the current to a value to be selected by the user and this he is doing depending which motor he wants to use. The answer of Old Steve did apparently shown he didn't know what I was targeting too. Sadly many feel that when new knowledge about a topic is presented they feel offended personally considering that they know everything there is to know they already know! The fact is that opposed to what dear Old Steve is writing, many do not know what the PWM is for and that it is available even in now pretty outdated controller circuits like the pair L297 and L298. I did clearly point to the fact I was taking about bipolar motors only not denying that in certain applications there are good reasons to decide for a different solution!
Otherwise I would need a good regulator capable of high current to drop the voltage to 3V to use motor 2.
This sentence my dear Old Steve is not correct. Basically any stepper motor control circuit does include the PWM to limit the current flowing through the coils. You do not need any external device but a resistance connected to one of the pins of a component to define to what current the PWM should limit the current. When you have to choose between to motors like the number "1" and "2" I took as an example it makes more sense to choose the number "2" because this motor does not need 4 A, it can live with 4A of current! In the L297 datasheet, really an outdated device Pin 15 sets the Vref value. I state what is written on page 3 of the L297 datasheet:
Reference voltage for chopper circuit. A voltage applied to this pin determines the peak load current
So this is just general basic knowledge of today but often unknown. I recently attended a webinar from EEDesign about motors and the presenter did not address this issue at all!
The fact is that speaking with expert users one made a nice comment about stepper motors. he said that he knew what stepper motors are because he had hurt his arms frequently when dealing with them when touching such a motor accidentally! That gets me to another fact I would like to present, knowing that certain experts here do know the topic! I am just now going to talk about about power and torque made available by the stepper motor comparing motors "1" and "2" again just as examples. Heat dissipation is coming from different sources within a stepper motor but it is valid to write that a coil using a cable capable of handling a current of 4 A has a smaller internal resistance then a motor where just 1 A of current is possible. So the heat dissipation due to the internal resistance of the cables in the coils is smaller in motor 2!
Lets now go on by looking at a diagram that shows the torque of a certain stepper motor against the stepping frequency:
The 4 curves in this diagram are to my personal opinion a good orientation to address the aspects of a stepper motor I would like to address in this chat, again welcoming critics, questions and additional inputs!
Lets go by parts! A simple bipolar stepper motor has its 2 phases and just 1 coil per phase. But if you take the third picture to the right of the first row and you compare it with the second picture on that same row you can see that the second picture is just a motor where the 2 coils in series are connected in series and that point brought out of the motor as a "center point" connection. To explain the meaning of the 4 curves never the less the third picture is more useful! If you now look on the third picture of the second row you can see that the 2 coils have been connected in series, while on the single image in the third row the two coils of a phase have been connected parallel! So 2 of the curves display information about the technical data of the same motor with the coils of a single phase connected parallel, while the other 2 show the information regarding with the coils connected in series. The diagram looks at the data connecting the motor once to 24 VDC and once to 48 VDC!
The diagram shows the torque available at the stepper motor for all 4 configurations and at both voltages against speed, which is equivalent to frequency of stepping of the stepper motor! Again risking to be seen as condescending and by no means being this my intention here my second question:
1. Why is the torque available from the motor getting smaller while the stepping frequency is increased?
2. Why are the 4 curves showing different behaviour and why are the torque over speed variation of the same stepper motor nearly identical when comparing the first curve with 4.2 A at 24 VDC identical to the curve of this same motor but with only half the current but at 48 VDC?
Just a short justification from me. I am presenting this as a chat and not as a tutorial to promote talking over the topic. Hopefully dear Old Steve will overcome its offense feeling and I would like to state what an old greek philosopher said about having knowledge: I know more then all the others, because I know I do not know! I am always searching to find areas of knowledge I do not have so that I can learn and to be advised when I am wrong, because only this way I can correct my wrong knowledge!