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I have an A4988 and a NEMA17, when I set the current limit to 1.5 A and the motor runs at a low speed of 0.2 RPS I measure the current and effectively it draws 1.5 A.

Now when I run the motor with the same limit current but with a speed higher than 6 RPS, the current drawn by one of the phases drops to about 0.6 A. Why?

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  • \$\begingroup\$ All motors draw less current at higher speeds, that's a direct consequence of the physics behind motors. \$\endgroup\$
    – Hearth
    Nov 19, 2021 at 14:21

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Basically because there is no back-EMF when the motor is turning slowly or not at all. Then the current is then only limited by the winding resistance. When increasing the speed, the back-EMF increases so that the current draw gets lower.

Of course, if you load the motor heavily it can draw pretty much as much current at high speed as when going slow.

The same applies to pretty much any electric motor. Only difference from for example a brushed DC-motor is that with the DC-motor the only way to get it to rotate slower without lowering the voltage, is by applying a load. AC motors can be slowed down by decreasing the frequency, but if you apply full voltage at low speed/frequency, the motor will draw a lot of current.

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