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# Reduce the output current from a stepper driver

I have to control 2 stepper motors with a single driver (multiplexing one at a time) and both motors are different, one 1.7A and the other 0.4A, if I set the current to 1.7A the 0.4A motor can burn out. Is it possible to put resistors at the output of the driver to reduce the current? How could I calculate it?

edited: the motors are

1.7A=17HS4401S, resistance per phase: 1.5 ohm

0.4A=JK42HS34-0404, resistance per phase: 30 ohmstepper-motorstepper-driverShareEditFollowFlagedited 47 mins agoasked 54 mins agoRicardo Casimiro17566 bronze badges

• 1The motors may already have different resistances. Add this info to the question. – Brian Drummond 52 mins ago
• I am confused. How can you “set the current to 2A? – tlfong01 47 mins ago
• 1@BrianDrummond edited – Ricardo Casimiro 47 mins ago
• 1@tlfong01 the driver (a4988, is the most popular) have a potentiometer and you able to set current up to 2A – Ricardo Casimiro 46 mins ago
• @Ricardo Casimiro, I vaguely remember that for either microstepping or non-microstepping step motor drivers, I don’t need to “set the current”. I always thought that the current the driver drives the motor is “set” or “decided” by Ohm’s Law, less motor coil resistance means more driving current, with the limit of the max current specified by the driver. Of course I assume your power supply has a constant voltage. – tlfong01 36 mins ago
• 1I think you’re going to have to use two different A4988 modules if you need to have two different motor current limits set. This module has only the onboard potentiometer to set the max current and there is no means provided to set it programmatically or from another input. – jwh20 28 mins ago
• In other words, the motor current is “set” by the Vmot according to Ohm’s Law, where Imot = Vmot / Rmot. So one solution is mux the power supply voltage at the same time. – tlfong01 28 mins ago
• And multiplexing or demultiplexing two PSUs to one A4988 Vmot input is not that complicated, eg, you can use two P-Channel MOSFETs, one to switch PSU1, another to switch PSU2. But it is not worth your time, because A4988 is so dirt cheap. 🙂 – tlfong01 21 mins ago
• I must apologize that I used a couple of stepper motor drivers, but never A4988. So my comments and suggestion might be nonsense to A4988. You mentioned an “on board pot” which I think is for over current protection, not for operating current setting. – tlfong01 17 mins ago
• Ah, you remind me one thing. I did once played with the big driver similar to the following: MP425 motor driver: nl.aliexpress.com/item/… /to continue, … – tlfong01 7 mins ago
• For this kind of industrial grade driver, there is a DSP (Digital Signal Processor) and current sensor circuits that can do the fine “micro stepping”, by very quickly switching on and off the motor coil current to set the peak and rms voltage, for max efficiency and performance. I must again apologize that I am just scratching the surface of microstepping knowledge, so no guarantee that I am not talking nonsense. 🙂 Ah, bed time, See you later. Cheers. – tlfong01 just now   Edit