Hi. There's a saying that there are no stupid question, but this one might break the rule...
I'm working on a project involving 2 steppers. I managed to find 2 used ones, NEMA23, 1.8 deg/step, 2.1A/phase. The guy who sold me opened the back seal to oil them, but they were relatively cheap and I didn't think it could cause any problems.
I've tried using Adafruit MotorShiled to drive them. They requre 2.1A per phase so I ended up piggy-backing 5 x L293D all together (per motor), 5th one was kinda by accident as I was certain that motor label said 2.8A per phase for some reason. I calculated that it would give me a nice 0.6 x 5 = 3.0A per phase and 5A peak. It was overheating and the heat protection was kicking in making motors buzz, so I decided to make my own drivers, basically using the same logic (as I know little about capacitors needed and such), use the same IC as it's the only one I could find in my country, put a heat sink backed with some silver paste on and I ended up with this:scheme
It's the same capacitor scheme as in MotorShield (I believe), without the rest of the stuff as I don't need it. The external computer supply provided for 12V/12A (at least rated as such) and I thought it would be enough even for doublestepping two motors.
It worked nicely for a while, or so I thought. The motors ran nicely for a while, were hot like hell, and then one of them started skipping. I opened it up and realized one of the wires desoldered. I soldered it back in and continue to test.
Today, there was a foul smell and one of the motors (the other one) skipped like crazy. I opened it up, hoping it might be the same problem, but no: it melted inside, one of the coils swollen up, blocking the rotor.
Both incidents happened when playing with interleaved and doublestep signals. Both incidents happened while motors were connected to a big pieces of aluminum used as a heat sinks.
I'm planing on getting 2 new motors this time, but I don't want to burn them too. Can anyone help and explain the current issues I might not be aware? Are the motors getting too much to handle and is that the reason for them dying (duh)? Should I get higher current rated motors, and if so how much?
Will 2.8A/phase ones be ok or will they have the same issue? Is it better to have motor rated more than the driver can provide?
Money's running tight and I need to get the motors ASAP so I have only one chance at this.
Thank you for reading this wall of text and for all your help.