Its just ohms law where current = voltage/resistance this is (almost) all. Usually V and A are given, but can deduct directly the resistance and even wattage.
A dc motor has this voltage rating on it and it is the value to run the motor at, because it only has dc in it, no controller, no other current limiter, current stays dc with same polarity. So the coil resistance does the magic thing and naturally limits the current (the current's natural target or the value it aims at, but still). The coil can have any other resistance, and if it would have zero resistance, would put the source in short.
A stepper motor does not use technically dc, the driver input gets dc, but output is say ideally square wave with some frequency reversing the polarity, which is not dc, but actually its more like ac. And the driver also limits the current, so the coil resistance doesn have to. Because of this, the coil has some freedom to have much lower resistance than an equivalent dc motor would. And this is beneficial, because the current rises much faster if its resistance is lower than previously. And the coil doesnt get burned because the driver senses and limits the current before it reaches any dangerous limit.
So both for the dc and stepper that voltage is the voltage given by the coil resistance and an estimation of coil current (for dc is rating, for stepper is more like max). For dc it is a voltage to run the motor at. But for stepper, you are much better if you actually run the motor a a voltage much higher than that.
A dc motor has this voltage rating on it and it is the value to run the motor at, because it only has dc in it, no controller, no other current limiter, current stays dc with same polarity. So the coil resistance does the magic thing and naturally limits the current (the current's natural target or the value it aims at, but still). The coil can have any other resistance, and if it would have zero resistance, would put the source in short.
A stepper motor does not use technically dc, the driver input gets dc, but output is say ideally square wave with some frequency reversing the polarity, which is not dc, but actually its more like ac. And the driver also limits the current, so the coil resistance doesn have to. Because of this, the coil has some freedom to have much lower resistance than an equivalent dc motor would. And this is beneficial, because the current rises much faster if its resistance is lower than previously. And the coil doesnt get burned because the driver senses and limits the current before it reaches any dangerous limit.
So both for the dc and stepper that voltage is the voltage given by the coil resistance and an estimation of coil current (for dc is rating, for stepper is more like max). For dc it is a voltage to run the motor at. But for stepper, you are much better if you actually run the motor a a voltage much higher than that.