I am working on a project that involves moving stepper motors, and the device will have to be on for upwards of hours. I am moving the bipolar NEMA17 stepper motors using a Protoneer CNC shield V3 on top of an Arduino UNO and DRV8825 stepper drivers. Though I haven't left the motors on for too long, whenever I do for longer periods, maybe 5 minutes or more, smoke starts being emitted around the 4 pins I connect my motors with. My question is that, if anyone has had a similar issue before, if they could explain why this occurs. I would also like to know if the stepper drivers are actually being protected by the heatsinks, because they can get ridiculously hot even after a few minutes and I'm worried that they wouldn't be able to last more than 15 minutes before exploding. Hopefully there's enough information here for someone to understand what's going on, but I'd glad to give more if that helps get a better idea of what's going on here. Thank you!
Those NEMAs are big ones - i suspect too big for the little A4988 chips - which can only provide 2A when actively cooled and generally only for short periods. I wouldn't try to push more than 1.7ish Amps for any length of time.
You will also need to set the vREF correctly for the motors you are using - if this is not set you will either provide too little current or too much current.
Look up the specifications for the NEMAs you have - and upgrade the Stepper controller to something more like a TB6600 that can handle greater current.
Also when the Steppers are not being used - disable (if you dont need them to hold) this will turn off the drivers and let them cool between runs/moves.