A4983 strange behavior

I am attempting to drive a 4-wire bipolar Nema 23 motor, 1.2ADC, 8.4ohms with the Pololu 1201 A4983 carrier. (See attachment for connection details and more specs).

I am powering the motor with 24VDC. I know that ideal maximum motor voltage is 1.2A * 8.4ohms = 10.08V, but I assume the current limiting feature of the A4983 will allow me to use 24VDC. This ok right?

I left the MSx inputs floating because they are pulled down internally with 100kohms. I want full step operation. I have *SLEEP and *RESET pulled high through 10kohm on my board.
I keep the *ENABLE signals high until I want to move the motors. At that point, I drive the *ENABLE low and the drive the STEP/DIR inputs. After I am done moving, I drive *ENABLE back high.

I am able to make the motors move, but I observe the following indicating something is wrong.

  1. The torque seems too low. I made some coarse measurements and the motor seems considerably weaker than its specs.
  2. When I step the motor faster than about 1k steps per second, the motor makes noise as it receives the pulses, but it does not move. I would expect to be able to move the moter faster.
    CT Series Stepper Catalog.pdf (91.1 KB)


As it says on the product page, MS1 does not have an internal pull-down, so you should do something with it. The 24V part is fine; that’s actually what you need to do to get faster step counts. If you don’t have much torque, your current limit might be set lower than you think it is. Do you have a heat sink on the driver? Without one, the maximum current you can get before overheating is around an amp; if the chip is not extremely hot, you are probably setting a lower current than you think. That might also affect the step rate. What kind of a step rate are you able to achieve? Make sure your code has enough resolution so that you’re not actually doing something like going from 500hz to many kHz by reducing some delay from one millisecond to zero.

- Jan

Thanks for your prompt reply. I missed that MS1 was not pulled down internally. I will connect it to ground and see if things change.

I will double check my current limit (i.e. REF voltage). Just to make sure, I should apply motor power when setting this limit, with the A4983 enabled right? I may have only had the logic supply on when I set the pot originally.

You asked if I was using a heat-sink. I am not.

You also asked what kind of step rates I was able to achieve. I can run at about 1000 steps/sec. However, I would expect to be able to go to at 10,000 steps/sec or 10,000/200 = 50 rotations/sec = 50 * 60 = 3000 rotations/min.


If you are measuring the voltage on the ref pin, the motor supply should not matter, but having it there should not hurt, either, as long as you don’t accidentally short something while making the adjustment. I think that past a thousand steps per second, you’re going pretty fast for a stepper, so you have to pay attention how you get there (i.e. accelerate appropriately). There can also be multiple resonant frequencies where torque gets low, so you have to avoid those.

- Jan