Erratic Motion from A4988

I am trying to make the Pololu A4988 Stepper Driver work with my Arduino Uno. I want to have the stepper rotate 90 degrees in one direction pause for couple seconds and then rotate back

In my Arduino sketch I have it:
send 50 step pulses separated by a 10ms delay
wait 2 seconds and change the direction pin

My problem is that this works as expected for about 60 seconds and then it starts acting erractically, stepping in random directions even when it shouldn’t be stepping (I can shoot a video if need be)

What am I doing wrong? Why does it start behaving erractically after a short time?

I have it wired up as recommended by the simple wiring plan on the product page
( Page: )

I have an 1.3 amp adjustable wall wart style power supply set on 10 volts powering the stepper

I have a stepper motor who’s label reads:
1.53 V
0.51 ohmn
1.8 Deg


It sounds like the chip might be overheating. What do you have the current limiting set to? You can’t practically set it higher than approximately 1A per coil without doing something extra to cool it.

Edit: I just noticed that your wall wart doesn’t actually supply that much current, so it might be the thing that is having trouble too.

- Ryan

I have a heat sink attached it via thermal tape. When it starts acting funky the heat sink is hot, though not enough to really burn skin.

I am not certain what the current limiter is set to (I need to get a new multimeter that can measure current above 200ma). Which way should I turn it to lower it?

The wall wart should be supplying 1.3 amps is that a problem because the stepper is rated for 3 amps? I figured I was just get less torque out of it

Thanks for the quick reply, btw.

Turning the pot counterclockwise decreases the current. If your multimeter can measure voltage, you can set the current by measuring the “ref” voltage.

- Ryan

Oh boy, I think this might be the first time I get to use ohmn’s law in a practical way!

To measure the REF do I probe between ground and the little circle that is connected to the trace that runs to the third pin from the left on the bottom of the chip?


- Ryan

Given that I have this heat sink attached:

What current should I aim to set the limiter to?

Also you mentioned that my power supply might be problem. Can you expand on that?

Unfortunately, I don’t know what you can set it to with that heat sink, you will have to experiment. You said your power supply can only source 1.3 A, so you want to set it low enough so that the voltage from your regulator is not dropping when the motor is drawing current. If your multimeter could measure current, you could measure how much you were drawing from the supply!

- Ryan

Ok, I upgraded the power supply to an ATX power supply out of an old computer. The 12 volt rail is capable of 15 amps.

I also, got a better multimeter that can measure the amps from the driver, and I now have the current limiter set at .7 amps

Unfortunately, its still acts weird after a couple minutes. I did three tests where I timed how long it took to start acting erratically and measured the temperature of the heat sink at the time of failure.

It consistently takes about 3 minutes to start acting up. And the temperature of the heat sink (as measured by a thermocouple and my fancy new multimeter) was 183, 185 and 148 degrees Fahrenheit.

What is going on? The driver should be able easily handle 1 amp without a heat sink, right? Why is it overheating?

Sorry I did not notice sooner, but someone here pointed out to me that your motor wants to draw 3.0A at 1.53V so in your 12V setup it will want to draw approximately 24A. Probably the current is overshooting the current limit you configured and the chip is overheating. Since it seems like it is working for a while, you might be able to solve your problem by limiting the current even more, or lowering the drive voltage.

- Ryan

I am afraid I only have 3.3, 5 and 12 volt at my disposal, and if I power it using the 3.3v nothing happens at all (presumably because the driver needs 8 volts minimum. You are right about lowering the current further. If I put it down to about 300mA it seems to be able to go indefinitely. Monitoring the temperature with the thermocouple shows that the temp gets up to about 140-150F and stabilizes

It sounds like these drivers and these just won’t work with each other the way I had hoped.

Out of curiosity, how did you figure it is attempting to draw 24 amps?

Should this driver be able to work with a small .28A 24v stepper motor running from my 12v power supply?

12 V / 1.53 V * 3A = 23.53 A

Is the motor rated to draw .28A at 24V? It will probably work.

- Ryan

To expand slightly on what Ryan said, the motor will try to draw current proportional to the voltage it is being supplied with. If it is rated at 1.53 V to draw 3 A, increasing the voltage to 12 V will proportionally increase the current it draws to 23.53 A.

- Kevin