Problem with Stepper Motor Drivers

Other Hardware Motors, Mechanics, Power and CNC
1

Hello everyone,

My Setup

I recently acquired some Nema 17 stepper motors, a 24V 15A (360W) DC power supply, and A4988 drivers. I connected everything according to the datasheets, using an Arduino Uno as the control unit.

What I have done

However, my motor refused to start. I attempted to modify coil connections, but there was no change. It caught my attention that the A4988 driver was becoming excessively hot, despite the presence of a heatsink and thermal protection, which the driver should have, as far as I understood.
To avoid damaging my drivers, I switched to an L298N (changing the code on the arduino obviously). Initially, I intended to power it with 12V, and the motor began performing as expected. When I supplied 24V, the motor operated for only a brief period before shutting down. Subsequently, I tried 18V, and it functioned for a considerable time, but the L298N driver still became considerably hot. These L298N tests were conducted at 300 rpm. Lowering the rpm to 60 at 18V resulted in the same behavior as 24V at 300rpm.
After all that, I tried switching back to the A4988. However, I noticed, using an ammeter, that Vmot was short-circuited to ground. I believe this could be a consequence of a previous failure. The L298N, despite the heat, were ok.

My personal conclusions

I believe that the original A4988 drivers might not be sufficient for my Nema 17 motor. Additionally, since a stepper motor is an inductive load, the lower the rpm, the lower the impedance, and consequently, the higher the current. Therefore, when I tested it with the L298N at 300rpm, it had no issues. However, when I increased the voltage or decreased the rpm, the driver heated up because it couldn't handle the required current.

My questions

Do you think these considerations are accurate? If not, what might I have overlooked? If they are correct, do you believe using a TB6600 could provide better results?

Thank you very much. Please feel free to share with me anything you need for a better understanding.

DATASHEETS

A4988 Chip:

A4988 Carrier:

Nema 17:

L298N:

2

But even with a heat sink and a fan blowing on the heat sink, the little thing is only rated at 2 amps maximum. That is 1 amp per winding on your unknown stepper motor. No where did you mention setting the maximum current for the board. Consider getting a proper driver board.

3

Hi, thanks for the quick response.

As I wrote, I'm using a Nema 17 stepper motor (attached datasheet) with a rated current of 1.5 Amperes per phase. From what I understood, the A4988 chip should be able to deliver 2 Amperes per phase, not in total. Apparently, I got it wrong. Do you recommend changing the driver? Do you think my considerations about the situation could be correct?

Thanks a lot again for your time.

4

The link that Google returned made NO mention of phase, just 2 amperes maximum with forced air cooling. Changing driver is entirely up to you.

5

2A is too much. Even with active cooling 1.5A per coil is borderline for the A4988. It is very important to set the coil current correctly. You do not have to set it to the rated current of the motor. If the torque is sufficent for you, you can set it to a lesser value - motor and driver will get less hot.

The ancient L298N is definitely not a suitable driver for your stepper and you may damage driver or stepper when using it.

A TB6600 may be an alternative - but there are also other small boards compatible to the A4988. E.g. the DRV8825 may be better able to handle the 1.5A of your motor.

6

Thanks for your feedback.
I'm actually thinking about the TB6600 as a replacement option. Do you believe that with a driver like that, I'll be able to unleash the full potential of my Nema?
And what about the DRV8825, which you suggested? I went quickly through the datasheet and it seems that it could supply 2.5A per coil (absolute maximum rating, but the motor requires 1.5A).
Also, do you think my thoughts on the issue could be accurate? I want to make sure I grasp the problems related to my situation.

Thanks again for your time!

7

The TB6600 can definitely handle the current of your motor.
It is important that you select a current controlling driver ( which the L298 is not ) and set the current according to your stepper. With higher voltages the driver is able to achive this current even with higher speeds. So you will lose less torque with higher speeds

8

As well as starting under a larger load.

9

Wouldn't that depends only on current, which could still be high since the impedance would be low (because the rpms are low)?

10

No! it depends on how quickly the driver can ChANGE the current from zero to max.

11

Now I understand, thank you!

12

To explain a bit further for you. ALL motors move because of the changing current/magnetism. DC motors with segmented armatures move because the current/magnetism change VERY rapidly because one set of contacts quickly turn off while the next pair begin to conduct. Stepper motors are identical, except electronics do the switching instead of the segments on the armature.

13

That's one reason why acceleration is important when starting the stepper. With acceleration the RPM is low at start, and the driver doesn't have to change the current quickly.