keep burning these pololu drivers..

the first pololu driver (w/ 4983) was getting control and logic-power from my arduino, and used with external 12V to drive a bipolar stepper. It went ok, and then -- in order to get higher rates, I followed some advices and connected it to a 32V/2A power adapter. While tweaking with its current limiting pot -- it suddenly burst into flames!

with the second pololu driver (this time w/ 4998 which include some shut down protection), i was more careful. I used it only with a 12V power (ATX PSU) and with the minimal current limit i could use (~halfway span of the pot). the chip (4998) was too hot to touch, so I included some 'nut' as an improvised heatsink. after several minutes of use - it died (no flames/smoke/smell this time).

toward my third try -- i humbly (and desperately) ask you for some tips...
do i need better heatsink (w/ fan maybe)? some capacitors/diodes/fuses that should be added somewhere? anything else...?

thanks in advance!
rubin

I ran a motor hot enough for a few months that the coating on the coils in the motors started to short out. When checking for continuity between coils it appeared the motor was fine until I checked for really high resistance (max on my multimeter) where I found it had a few million ohms of resistance between them. It would work for a while and once warm it would short out even more and burn out the driver. This may be your issue too.

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One feedback I got about the Pololus is, the user accidently used bridged pairs of screw terminals. So, a solid connection between A-B and C-D. The Pololus (A4983) survived that easily.

Allegro's data sheets also considers the A4983 to be overtemperature-resistant. Matches my experience, where overheating simply results in dropouts.

So, there might be some other issue with your setup. Which schematic do you use?

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I'm using the suggested schematic as appear in pololu:


with the motor power supply is a computer ATX PSU, and arduino nano as the controller (which also powers the A4988 from its 5V pin). the stepper motor i'm using is: PK266-02A

I think the only thing you can do is to pull the Pololu out of it's socket and measure all the pins, wether there is a voltage above 5 volts somewhere. Except for the VMOT pin, of course.

Putting 12V into the signal pins does destroy a Pololu, as you notice quickly if you insert it the wrong way.

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35V is the absolute max rating for the chip so not a good idea to run it from that voltage especially as back EMF can cause the supply rail voltage to rise.

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does using capacitors might help?

Capacitors would help with voltage drops. Is this at a low speed, or are you just trying to push as much power in as possible? Your second chip might work now that it is cooled down. I recommend you get a tray of ice and a small fan, so you are blowing cool air over the chips. Also, did you apply all of the 35V 2Amp to one chip, or was it distributed amongst the 4/5 motors?

I've had 2 of them go bad, as well. Running the VMOT from 19V, VDD from USB. The current is set to < 1A and they are heatsinked. Even if they were to get too hot, isn't the thermal shutdown supposed to handle that w/o damaging the chip? Does the sequence of powering up VDD and VMOT matter? I don't see anything in the spec sheet for the A4988, but I've noticed that the TB6560 is sensitive to the sequence, requiring VDD on before VMOT. Does the A4988 have a similar requirement? I'm afraid to play with them again until I figure this out. I'm just following the wiring shown in rubin's post above.

Did you disconnect the motor while there was power to the chips? This seems to be the most common failure mode.

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No, I'm very careful about tight connections and not disturbing them while powered up.
Does anyone else have issues with power on sequence of VDD/VMOT?

Andrew Diehl Wrote:
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> Did you disconnect the motor while there was power
> to the chips? This seems to be the most common
> failure mode.

Are you running a custom electronics or firmware? Why would your power on sequence be different? Power on sequence could be an issue if your setup is radically different from others. In general you want the logic (5V) to be stable and the motors disabled before you add 12V power and then enable motors. Power off is reverse of that. Also check the datasheet, especially if you are doing new things with circuit or firmware.

I was running them on different supplies, and sometimes, I would forget to turn off the 12V supply when the 5V was turned off.
It seems like it's OK to do that for a few seconds, but for longer periods, it's not.
I didn't see anything in the spec sheet saying that the logic supply needs to be turned on before the VMOT.
I know the TB6560 has a specific sequence, but I don't see any similar language in the A4988 spec sheet.