So how common is it to burn-up a pololu module?
My Y suddenly stopped working and if I swap it with my X on the RAMPS board it works again, so I suspect the module but I’m wondering if there’s any other stuff I should try before resorting to ordering parts…?
Others may argue, but I don’t think it’s hard at all. I blame insufficient cooling and over current on mine burning. If your motor is getting hot, the step controller is probably as well. It doesn’t hurt to have extras. I bought 2 for less than thirty bucks off amazon, I wanted the 2 day shipping. Be sure to turn your pots down as low as you can without shipping steps. This saves derating the step controller and the motor.
Cool, good point about the spares, I’ve got close to two years out of these so far and I’m not exactly gentle with them 
Honestly I’m a bit relieved because early on I had a failure with one of the MEGA pins that took out my second extruder channel (fortunately I only need one :).
The Y definitely gets the biggest work-out, the carriage is heavy and doesn’t like to stay adjusted, so it’s no surprise that it was the axis to fail first, but I figured I’d check and see if there was something other than the simple “swap axis”.
I burned out at least a dozen of them when I was trying to use them on a breadboard, mostly due to poor connections or mis-wiring because of the pin labels being on the wrong side. It’s much harder to kill one that’s plugged into another circuit board. One likely cause is breaking the connection to the motor while it’s energized, which could happen by unplugging the driver or the motor, or by having a loose wire inside the motor.
The DRV8825-based drivers are much more robust.
Yeah it’s entirely possible @Whosa_whatsis that my cable is flaky and could have caused the failure. I’ve been careful about messing with them when the power is applied, but anything is possible
I ordered a couple replacements and we’ll see what happens. If I get ambitious before the show up I might swap one of the “known-good” ones from another access into the socket for the Y just to rule out it being an issue elsewhere (although since I’ve already ordered parts it’s sort of a moot point).
Thanks @John_Ridley . Is it also possible to smoke them by hand-cranking the steppers too much (or perhaps messing with wires while you are moving the steppers by hand)? They do make pretty good little generators…
@Jason_Gullickson While it’s probably technically possible, the fact that they are connected to an axis that’s only a couple hundred mm long makes it very unlikely, as it limits the sustained current they can put out. If you move them quickly enough to generate enough current to do damage, you won’t be able to keep them moving at that speed long enough to do damage before hitting the end of the axis.
Cool @Whosa_whatsis then I’ll keep slapping the y-axis around 
I’ve never really burned them up. I’m still on the original set of pololus that I got 2 years ago. Granted, I have these bad boys on the tops: http://www.amazon.com/Enzotech-MOS-C1-MOSFET-Heatsinks-Pack/dp/B004CLDIHK/
That’s impressive @ThantiK !
I never noticed them getting hot, but then again I could probably miss something like that. I guess I’ll know soon, and if a replacement doesn’t do the trick I guess I’ll have some spares and will have to dig deeper into the RAMPS & MEGA…
Heatsinks are nice. The chips are actually designed to sink heat away through the PCB, which is pretty small in this case. They should really be on the bottom of the PCB, with the heatsink on the opposite side. This is how the panucatt drivers are built.
Still have my original set from two years ago as well, also fitted with heatsinks of similar size. On all five printers that i’ve built and run so far, the only things that have ever killed a driver were a) unplugging motor wires while powered up or having loose connections and b) moving an axis too fast by hand without a PSU connected - that can create a massive voltage spike that isn’t eaten away by a DC-DC converter. Ok well, that totalled my first Saguinololu and not just the driver.
@John_Ridley , what are the specs of your motors? I would think that a higher phase resistance would mean less heat, not just because of lower instantaneous current when the FETs cycle on, but because the higher duty cycle means longer on-time (they generally have a fixed off-time), and thus lower switching frequency. This allows them to run more efficiently and generate less heat, but also reduces their ability to accelerate quickly and maintain torque at high speed.
The strength is a function of the number of windings, the current going through them, and the strength (size) of the permanent magnet(s) on the rotor that the electromagnets act against. That last variable is a big reason that larger motors tend to have more torque, though the larger motors also have room for more windings without using thinner wire that will increase resistance and decrease current.
@John_Ridley the higher-resistance ones will typically also have a higher inductance, which doesn’t matter much when standing still, but will require a much higher voltage to change the current through the coil. This induced voltage will more easily reach the level of your supply voltage (and then limit the pace at which the coil’s current changes, thus limiting the maximum speed and force when moving) when the motors have a high-ish inductance.
Man I’ve missed you guys
So this is interesting. I picked up a couple of drivers based on the a4988 and when I swap out the Y driver with one of these new ones, the MEGA won’t even light up…
I double-checked the pins to make sure I’m putting them in the right way, and I’m going to double-check everything else, but have you seen anything like this before.
Ah ha! Just took some fiddling with the pot, the Y axis lives again!