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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? enter image description here

edited: the motors are

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

0.4A=JK42HS34-0404, resistance per phase: 30 ohm

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    \$\begingroup\$ The motors may already have different resistances. Add this info to the question. \$\endgroup\$ Feb 22 at 13:39
  • \$\begingroup\$ I am confused. How can you "set the current to 2A? \$\endgroup\$
    – tlfong01
    Feb 22 at 13:44
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    \$\begingroup\$ @BrianDrummond edited \$\endgroup\$ Feb 22 at 13:45
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    \$\begingroup\$ @tlfong01 the driver (a4988, is the most popular) have a potentiometer and you able to set current up to 2A \$\endgroup\$ Feb 22 at 13:46
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    \$\begingroup\$ I 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. \$\endgroup\$
    – jwh20
    Feb 22 at 14:03
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It's possible if you have some high wattage resistors. Adjust your VMOT to give you the proper current through the 0.4V motor and rely on the internal chopper to give you the proper current in the 1.7A motor. Keep in mind that if you start chopping the output to control the current through the 1.7A motor, you will effectively decrease the applied voltage on the 0.4A motor so you'll have to get the resistances just right if you want to run both motors at their maximum current. If you match the motor current exactly, you will not be chopping at low speeds, but you may not be able to achieve high speeds with good torque because motor inductance is going to start dominating the current response and you'll have no way to control it. It would be significantly better and possibly cheaper to run with two separate drivers. High power resistors aren't cheap. You'll probably need 25W resistors to get the job done without starting a fire. If you drive the motors in series, you could use 7 Ohm resistors across the 0.4A motor windings. Then you need to drive VMOT with 15V. I don't think you'll want to try to microstep in any of these configurations.

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