2

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

Improve this question
4
  • Can you please provide your circuit diagram/schematic. I suspect your wiring is wrong.
    – sa_leinad
    Oct 1, 2017 at 2:54
  • Image of circuit added..
    – RLI123
    Oct 1, 2017 at 3:07
  • I see the circuit but not the adjustment pot referenced in the question, so can't answer yet.
    – SDsolar
    Oct 1, 2017 at 19:44
  • 1
    The adjustment pot is built into the circuit board and came that way. Rs is also built into the circuit. elegoo.com/product/…
    – RLI123
    Oct 1, 2017 at 20:25

1 Answer 1

Reset to default
1

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. ;)

Improve this answer

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.