Underpowering a high-amperage stepper
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Hello, I am trying to use this stepper motor, which has a current rating of 3.5A per phase. This is over the recommended rated current of 3A, but I was wondering if I can still use the built-in driver, but just run the motor at 60-80% so that the current is in the recommended rating. If this is not possible, I will look into using an external driver.
Thanks as always!
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Stepper motor drivers are Constant Current sources to the motor, which basically means it will adjust the voltage so that the set current is always reached and constant (unless the circuit is open or shorted). This means that one can run higher current rated motors, at lower currents without risk of the drivers being damaged.
That said, running the stepper drivers at close to their maximums, will require efficient cooling to prevent them shutting down due to thermal shutdown being reached (the drivers will protect themselves by shutting down if they get too hot).
In any case, it is a good idea to run motors at about 80% of rated current, as this will keep them cool (extremely hot motors can degrade themselves, and also cause other issues, especially the Extruder motor can prematurely heat filament in a direct drive system).
Just keep in mind that the rated current will produce the rated torque, providing less current will reduce the actual torque (most steppers have a graph in their datasheets that will give the details as to how much torque the motor should have at specific currents).
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Up to 60°C should be safe?
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The maximum current supported by the Duet is 2.4A peak per phase, so you will be running it at about 69% of rated current. It should perform reasonably well at that current. I run the motors on my delta print lower than that. Don't forget that you need good cooling of the Duet to run it at or near maximum motor current.