The stepper drivers are called constant current because that is what they are "trying hard" to do, that is their aim/objective only, not because they are actually achieving exactly that. The way of working the current is anything but "constant". Basically it senses the current rise/fall and it interrupts when it gets too high (Ipeak) and lets it flow when its undervalued again. That means at any time a coil is energized, at any specific point in time, the current is either on a rise or on a fall edge. This is "not exactly" constant. On the contrarily sort of speaking it is as "agitated" as it can be - can not figure a way of "exercising" the current more than that. What this is achieving, is not a constant current literally, but to be more precise the constant value is the *average* of the current. Even if the current is anything but constant, at least the average of it is constant.
However the current itself is either rising or falling, its always transitory, which is not exactly what i get for "steady state". For example i believe the "steady state" of a 1 ohm coil with a 12v supply would be 12Amps, ohms law, a value in which the current would be "steady" and not naturally rising nor falling anymore, an operating point at which the system would stabilize itself naturally. When the current is on a rise edge, that is the value the current wants to get to, even if the driver will interrupt it, that point dictates how the rise curve looks and thats the final current value at which it aims. Thats why a 24v supply would help, it would make this final point 24a instead of 12a, and with final at 24a the curve is shaped more abruptly sort of speaking (at least more abruptly in the short term / first part which is of interest). But if it would reach what i refer to as "steady state", if the current would reach the operating point needed to stabilize itself, like in any dc voltage applied to any load, current would rise at final current value given by ohms law, and if that would happen to a bipolar stepper most likely the coils or driver would burn. Sort of speaking, my opinion is that it does not have a "steady state", coz the current is always transitory, at any point in time the current either rises or falls, just never "stays put" in this case.
If i would have a 8 wire stepper (each half coils "medians" separated), wired/used in unipolar mode, coil resistance of 5ohms, and i put the coil edges at 5v, and the (separated) "medians" at low side mosfets, i would open a mosfet gate from uC and let the 5v flow through coil, the current will rise and in the end i would get 1A through each coil, then this will be steady state, because the current would of reached its final value dictated by ohms law. It wont go anywhere else, the current transition from zero to its final value reached the final value, its stable at that point. This is different drive method, this one reaching steady state and probably mostly sitting at steady state. This means i need stepper motor with coil resistance high enough so i can make use of coil resistance directly without the need to add other external resistors to limit the current. It will be slow, at 5v the coils will energize painfully slow, but will work, just wont be fast. So maybe an area of applications where the motor justs sits there and hardly moves at all, like opening and closing windows, or shutters, etc. This is exactly the other type of stepper motors (high resistance, high inductance) that are at the opposite spectrum of what would be required in a motor for a printer.
However the current itself is either rising or falling, its always transitory, which is not exactly what i get for "steady state". For example i believe the "steady state" of a 1 ohm coil with a 12v supply would be 12Amps, ohms law, a value in which the current would be "steady" and not naturally rising nor falling anymore, an operating point at which the system would stabilize itself naturally. When the current is on a rise edge, that is the value the current wants to get to, even if the driver will interrupt it, that point dictates how the rise curve looks and thats the final current value at which it aims. Thats why a 24v supply would help, it would make this final point 24a instead of 12a, and with final at 24a the curve is shaped more abruptly sort of speaking (at least more abruptly in the short term / first part which is of interest). But if it would reach what i refer to as "steady state", if the current would reach the operating point needed to stabilize itself, like in any dc voltage applied to any load, current would rise at final current value given by ohms law, and if that would happen to a bipolar stepper most likely the coils or driver would burn. Sort of speaking, my opinion is that it does not have a "steady state", coz the current is always transitory, at any point in time the current either rises or falls, just never "stays put" in this case.
If i would have a 8 wire stepper (each half coils "medians" separated), wired/used in unipolar mode, coil resistance of 5ohms, and i put the coil edges at 5v, and the (separated) "medians" at low side mosfets, i would open a mosfet gate from uC and let the 5v flow through coil, the current will rise and in the end i would get 1A through each coil, then this will be steady state, because the current would of reached its final value dictated by ohms law. It wont go anywhere else, the current transition from zero to its final value reached the final value, its stable at that point. This is different drive method, this one reaching steady state and probably mostly sitting at steady state. This means i need stepper motor with coil resistance high enough so i can make use of coil resistance directly without the need to add other external resistors to limit the current. It will be slow, at 5v the coils will energize painfully slow, but will work, just wont be fast. So maybe an area of applications where the motor justs sits there and hardly moves at all, like opening and closing windows, or shutters, etc. This is exactly the other type of stepper motors (high resistance, high inductance) that are at the opposite spectrum of what would be required in a motor for a printer.