A4988 (without regulators) Burn at High Step Rates

Support Motor controllers/drivers and motors
1

Hello all,

I’m new to the forum, and it’s unfortunate I have to start with a problem I’m experiencing.

I ordered several A4988 carriers (without regulators) from a UK distributor (who has suggested I seek help here), and now 4 of them have stopped burned/working.

Each of them have worked normally at low step rates (less than 2000 steps/second), but when I pushed them to higher step rates (20,000 steps/second), some of them simply stopped working, and some of them gave off the dreaded magic smoke. After the first casualty, I checked the entire circuit, and scoped all the supply voltages (motor supply is 12V, logic is 5V), and everything was normal. I placed another A4988 carrier in and everything worked fine until suddenly the driver stopped working again. The same went for the last 2 boards.

I limited the current to the motors well below the max current for the stepper (I was going for the high step rate instead of high torque), and there aren’t any problems with heat.

I’ve read the datasheet quite thoroughly, and did not see anything about a maximum step rate. Is this board actually rated to run at 20,000 steps/second, or is there some other problem?

Attached is an image of the circuit that’s causing the burning.

Hon

IMAG0255.jpg610×800 436 KB

2

Hi, Hon.

I am sorry you are having trouble with your stepper motor drivers. It is unlikely that the step rate is related to your problem. Could you tell me some more about your setup? What is your 12V power setup? Do you have access to an oscilloscope?

-Claire

3

Hello,

The 12V power supply is simply a power brick rated for 6A. I have used this power brick to over 5A without any problems.

I do have access to oscilloscopes, which I’ve used to check the supply voltages. There aren’t any significant spikes or anything.

Hon

4

I suspect that an LC voltage spike damaged your boards since the only electrolytic capacitor I see on your breadboard looks like it is connected to your regulator. With these spikes it is possible for you to damage electronics just by an unlucky application of power. You can find more information about LC spikes here:

pololu.com/docs/0J16/all

Could you post a close up picture of a unit that has burnt?

-Claire

5

Hello,

The units seem to burn differently, some show the damage externally, some not. I’ll post a photo when I can.

Hon

6

Sorry about the slow reply, here’s a picture of 2 of the burnt boards.

Theres no external damage visible on the IC on the left, but not for the one on the right.

Hon

2012-07-07 22.43.00.jpg2207×829 1.47 MB

7

Hmm, that does not look as catastrophically destroyed as I expected. On the one without visible issues, you are sure that smoke came out of the ICs? How long after the failure was power cut to them (for instance, does your power supply have some kind of short circuit shutdown mode)? I am still concerned about the LC spike protection, so I recommend you put an electrolytic cap near each driver carrier in the future.

I do not know if it will be enough to make up for the international shipping, but we might be able to get you discounts on replacements. If you are interested, please email us with a reference to this thread and your order information (e.g. invoices) for the damaged units.

-Claire