TLDR: motor overheats >200 degF and I don't know why.
I have a NEMA 14 stepper motor (14 N-cm) driven by an A4988. The logic is controlled by an ESP-32 WROOM MCU, and the motor is powered by a 24-V 10-Ah battery pack (these two in series). The battery is powering other stuff as well, to explain its size.
This is my first time using stepper motors. I'll walk you through my process here.
I tested one motor and one driver with the MCU using this guide, and everything worked great. Then I went ahead and integrated the MCU and five motor drivers into an existing system. I wired the drivers like so:
VMOT & GND to the battery, with a 47-uF 25-V capacitor across it, long lead on VMOT
VDD & GND to a 5-V power supply
Short between RESET & SLEEP
STEP & DIR to designated pins on the MCU (all ten MCU pins used here were checked in the prior test)
Then I connected a motor to one of the drivers (wired exactly as I did in the prior test), and powered it up. Immediately the motor made a high-pitched sound for about 20 seconds then went silent, and when I touched it, it felt at least 200 degF. The firmware I had loaded onto the MCU at this point would have been a much much slower rotation than what I had in the prior test, so I don't see any way it could be the culprit (here it is, just in case). I was in the middle of testing the serial communication from a parent MCU to this child MCU which was controlling these drivers, so there's a high likelihood that the STEP & DIR pins were low the whole time.
I don't think this overheating broke the motor, because I repeated this two more time with a similar result, but I think I did break it for good while trying to measure the current going through one of the coils, because it will not longer make noise or get hot.
I have a natural disinclination to electronics, so I can't make a lot of good guesses as to what's going on. I assume the motor was getting 24 V, since that's what the battery is rated for, and using P=VI, I assume there had to be a big current going the motor to generate all that heat. I just don't know why or how the motor was accepting all that current, since I assume the driver is mean to stop that from happening, and I quadruple checked that it was wired up right.
Any ideas?
