Hi everyone, I’ve been trying trying to get my 1.8amp stepper motors working good, however it seems i have blown a few black edition A4988’s. my question is should i try buying more of those or should i buy some DRV8825 clones?
First you should figure out why you are blowing your existing drivers. Allegro notes they are 2A capable (http://www.allegromicro.com/en/Products/Motor-Driver-And-Interface-ICs/Bipolar-Stepper-Motor-Drivers/A4988.aspx) so you if you’re blowing them up with 1.8A motors then you’ve got a bigger problem.
One problem that folks don’t pay enough attention too is the wiring to the drivers from the PSU, you really want that to be as low inductance as possible. A snubber across the power near where it feeds the board can also help in reliability.
Worth every penny.
I run twin 40mm fans, heatsinks, and run my motors at .4-.5v (setting the pot and checking with a dmm).
just realized that my stepper don’t actually say 12v. but i am using a 12v power supple.
and these are my motors http://www.ebay.com.au/itm/LearCNC-60mm-Nema17-Stepper-Motor-For-RAMPS-Prusa-Mendel-Rostock-3D-Printer-/201006654389?pt=LH_DefaultDomain_15&hash=item2eccee23b5
@Branden_Coates
What he said.
With the psu off. You can set with having the usb plugged in. Do that before you supply 12v to the board.
Vref should be .6v (I’d run less a tad that’s just me)
@Branden_Coates
I mean no disrespect here but the ONLY issue with a stepper motor is current when you use a chopper drive.
Yes, a motor will have a voltage rating, and that rating is determined such that a source of that voltage with unlimited current will be current limited by the winding resistance to a safe value. You can run the motor at 48V (which people do because you want to get to peak current quickly for faster response) and that is the benefit of a chopper drive. Once the desired current is reached, the chopper “turns off” the circuit. Once it drops below the trigger level it turns the circuit back on until the current is back to where it should be.
A motor driver failing is almost always due to an over voltage situation on the driver. So if the FETs in the driver have a forward breakdown voltage of 40V and you’re getting 50V spikes because you haven’t adequately snubbed the inductive kick from the chopper, you will toast the FETs.
The next most common failure mode is that it gets too hot too fast. The thermal resistance between the chip and the air around it, is called Rtheta(j-a) or Rtheta (junction to ambient). That is measured in degrees centigrade per watt. To compute the wattage you use the on resistance of the FETs in the package, and multiply that by the square of the current they are carrying. That time Rtheta will give you tell you how much hotter the junction is than the ambient air. If it gets above the spec, most chips will have a thermal shutdown (the 4988 has one) but that shutdown can be defeated if your temperature rise is faster than it can respond (for a variety of reasons it doesn’t respond instantly but most notably because the chip can handle brief spikes at higher current perfectly well).
A design challenge in a number of boards is that the ground wires from these drivers are very thin traces. If you’ve got four of the running (XYZ+Extrude) and you’re pulling 6+ amps through the drivers, and they all chop ‘off’ at nearly the same time, you will see a big “ground bounce” if you don’t have a solid ground plane design. Lots of robots people have seen this happen. It means suddenly your ground has a higher voltage potential, best case it resets you control processor, worst case ground voltage potential bounces above Vcc and you get reverse current flow in your chips.
I’ve built a metric buttload of motor drivers over the years, one that is operating within its design parameters won’t fail (it may fault out with an over current or over temp fault but it will self reset).
I think he can get in the right direction now
You’re not going to get much more than 1A drive capacity with the postage stamp drivers. And I recall you want to set the driver to 70% of the motor’s labelled current max anyway, leaving you around 1A.
Another failure mode of stepper drivers is killing them with spikes from the steppers. When setting up my machine I used to manually turn the steppers, inducing a voltage. I believe that is what caused my stepper drivers to fail when they are not protected by diodes. I used pololu drivers as well. Didn’t have time for furter testing yet. Can anyone with more experience add to this? How would the diode protection work?
if your stepper drivers are set right they’re not a consumable 
I did a post a couple of months back about how to figure out what they should be set to and (if I recall right) Tom posted some additional feedback that also helped a lot. Polou’s come in 2 versions and then the motors are different so you need to account for the driver and the motor and set them accordingly. on my one printer with the low current drivers and small steppers the ideal current is 0.4v and on the other printer that has higher current drivers and bigger steppers it should be 0.7v ( I think I run them between 0.5v and 0.6v)
thanks everyone for the input. i’m heading in the right direction now.