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I'm driving a stepper rated at 5V/1.7A using an A4988-based driver circuit with a 12V power supply. An Arduino controls the stepping sequence.

According to the datasheet for my A4988, I should be calculating Vref as:

Imax = Vref / (8 * Rs) so,

Vref = I * (8 x Rs) (where Rs is 0.1 ohm on this particular board and confirmed with meter).

So, Vref should be (1.7A x .8) or 1.36V to drive 1.7amps.

The problem is, I cannot adjust the A4988 to get Vref up that high.

With the adjustment pot full swing, the best I can get is .9 to 1V. When I energize and hold the motor and use an amp meter, the coil is drawing about .9 amps -- which is still less than the 70% of 1.7 Amps I would like (using full-step mode).

Is Vref potential limited by the input voltage of 12 volts? Is there something else I'm missing?

Thanks in advance.

Added: This is the circuit I am using: enter image description here

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  • Can you please provide your circuit diagram/schematic. I suspect your wiring is wrong. – sa_leinad Oct 1 '17 at 2:54
  • Image of circuit added.. – RobNY Oct 1 '17 at 3:07
  • I see the circuit but not the adjustment pot referenced in the question, so can't answer yet. – SDsolar Oct 1 '17 at 19:44
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    The adjustment pot is built into the circuit board and came that way. Rs is also built into the circuit. elegoo.com/product/… – RobNY Oct 1 '17 at 20:25
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You have a 30K resistor divider in series with the trimmer. Change the 30K resistor for one rated at 27K to obtain those higher values. ;)

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