Nema 17 with the A4988 black edition

Hi, I would like to know what may be the reasons why my stepper motor which has a current rating of 1.68A can’t seem to run properly when I use the A4988 black edition driver. I gave it a power supply of 12 V, 3A and use the standard connections(shown on the Pololu website) for the motor and the driver. Is it that the motor requires more current to run? Thanks. (also after testing the Vref always stays 660mv even if i adjust the potentiometer)


The black edition A4988 carrier can continuously handle about 1.2A per phase without additional cooling. You can use additional cooling to reach higher current limits, but I suspect getting upwards of 1.68A would not be very practical. Limiting the current to less than the rated per phase current will reduce the maximum power from your stepper motor, and depending on the particular motor and details of your setup, it might be difficult to use it at all. You might consider a more powerful driver; I suggest looking at the comparison tables on our stepper motor driver category page which list the max continuous current.

If you are unable to adjust the current limit and the voltage on the VREF pin, that is probably a different issue. Just to confirm, are you sure that you are actually turning the potentiometer? We have had a few other customers report similar problems in the past, and in several of those cases, it turned out that the tool they were using was too large to engage the pot, so they just thought it was turning endlessly when it wasn’t actually turning at all. We have also seen cases where customers damaged the potentiometer by breaking the end stops so it spins continuously, so please be careful to avoid that as well.

If you are sure you are turning the potentiometer and VREF still is not adjusting, can you post some pictures of your setup that show all of your connections?

- Patrick

Hi, my potentiometer is turning endlessly does that mean I can’t use, my A4998 driver? Also, my max Vref shown is 0.665 V after turning the potentiometer and it goes back to 0V when I turn even more. my connections are the exact same as the ones shown on the Pololu website. Also is it possible to recommend a driver? I do not need the motor to be using the full torque. any advice would be helpful thank you.

If your potentiometer is turning endlessly then it might be damaged (though it possibly might still be usable if you can keep the pot in its valid region). With one of our A4988 boards I would expect you to be able to see higher voltages by adjusting the potentiometer. Can you post some close up pictures that show both sides of your board?

As for an alternative driver, we have several that could work for your motor (especially if you do not absolutely need to maximize the power from it), so it is up to you to determine which features you want to prioritize. The comparison tables on the stepper motor driver category page would be a good starting point. I generally recommend prioritizing the ability to get the maximum possible power from your stepper motor (you can always choose to set the current limit lower, but you cannot make the driver more powerful). With that in mind if you want a board in the same form factor, then for a 12V supply and 1.68A motor I would suggest one of these:

If you have space for a larger board, then I would suggest one of these:

- Patrick

I see, also after I was able to get the motor running last week the driver got really hot is it possible that it may have overheated that the Vref can’t go above 0.665V? It can go below 0.665V but the value just jumps around and goes to zero when turned counterclockwise. Thank you for your recommendation and help.

It is normal for the stepper motor driver to get quite hot during normal operation, and the A4988 has an over-temperature thermal shutdown feature that should help protect it from overheating, so it is not clear yet if that is what happened to your board. Can you post some close up pictures that show both sides of your board like I asked for in my previous post?

- Patrick