How to melt a stepper motor

Summary: Power a 5V stepper with 12V, and leave most of the coils energized for long periods of time

I got one of the ubiquitous packs of 5 28BYJ-48 + ULN2003 stepper driver boards. It was 18.98$ CAD in 2018 for 5 – a very reasonable price. I like cheap things like this because I don’t know anything and I’ll wreck them for sure. Also, if you can get something to work with one of these motors, then it’s easy enough to swap out for a “real” stepper after the fact, so there are few downsides.

I tried to use one of these in a project and it was my first time doing so for more than a few seconds (or just enough to prove I could turn it). I’m using an ESP32, and specifically using the Espressif IoT Development Framework (ESP-IDF) to build the software. I didn’t immediately find a stepper driver library that looked nice , and I had the step sequence on hand, so I figured I’d write my own driver. It’s nothing fancy – an array of steps, and a loop that sets the 4 pins to the corresponding value for each step in the sequence.

The included ULN2003 stepper boards show that they can take 5-12V, and as they came with a 5V stepper I assumed (I know…) the board would step the voltage down and regulate it. All it does is pass the supplied voltage on to the stepper motor though, so if you want to run a 12V stepper – you give it 12V, if you want to run a 5V stepper… you probably ought to give it 5V. In my mind, I was doing the right thing as the higher voltage would mean less current and less heat. I now realize that’s wrong for more than one reason.

As I don’t know anything, I had it do a semi-arbitrary number of steps (500), then “sleep” for a couple hours. What I didn’t pay any attention to was the coil energization between these two rotation periods. If unlucky, it could be resting with 3 out of the 4 coils energized for the entire time. The worst part is there was no reason for it – there was no load on the stepper, so it really didn’t need to hold its position.

Anyways, these look like Nylon gears to me, which means almost definitely the motor got to over 100°C (which is pretty horrifying). Now I have 4 cheap stepper motors to play with…

I didn’t even notice until I posted the pictures, but it looks like the drive gear melted completely and turned into a puddle. I assumed I had lost it while taking it apart, but obviously this motor was even worse off than I thought.

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