I’m helping a friend build a printer which uses NEMA 14 steppers, however whenever we test the motors they get really hot, almost uncomfortable to the touch. They are 10 volt, 0.5 amp motors, and the supply to the RUMBA controller is 24 volts, I’m only testing a single motor at a time because I know that overdrawing voltage will likely cause a brown out or damage something. How can I prevent heat damage with these motors, asides from cooling them?
Fans are almost certainly the cheapest, fastest, easiest option. For rapid movement you want a fairly high voltage, to get current through the motor fast. That means lots of current draw. Ideally you’d use a driver that starts out with high voltage and then reduces it as the amperage comes up to what the motor needs, which is what chopper drivers do. But that requires extensive redesign.
For what it’s worth, on my cnc mill the motors get too hot to touch and they’ve been running for four years. I’m not saying it’s a good idea, just that almost-too-hot-to-touch is probably okay.
What are you feeding them from the steppers? Your v may be high
Depending on the drivers you’re using, you probably want to turn them down to their lowest setting for a .5A motor, although your description of “almost uncomfortable to touch” sounds like you have it set perfectly.
@Whosa_whatsis and @John_Bump , so what you’re saying is that hot motors are fine as long as they function properly. I’m not having any real problems with these other than the heat, and I’m 99% positive that the drivers are tuned right (unless gremlins are afoot)
I might talk him into buying some fans though as the heat could wreak havok on the PLA parts in his machine.
If you can mount the fans so they’re blowing air away from the machine, across the steppers, that will deal with the thermal disruption.
But it’s generally okay to run steppers somewhat hot.
The rule of thumb is that if you can hold the motor for a few seconds between your fingers without pulling your hand away in pain, they are running within their specifications. This may, however, have an adverse effect on the parts they’re mounted to if they’re made of PLA. You should never make printer parts out of PLA.
@John_Ridley You’re probably not getting the full rated torque out of them then. That’s fine if you’re not getting skipping, but you could be getting the same toque with smaller and lighter motors if you were willing to let them get hotter.
My advice against making printers out of PLA is not just a matter of motor heat. I’ve seen printers that were left in cars or even operated in particularly hot rooms literally fall over due to their PLA parts softening, and many more examples of more minor overheating causing alignment issues, slack belts, misshapen prints, etc. due to harder-to-diagnose effects of PLA parts getting warm and not holding their shape.
have you tried sticking heatsinks to the stepper? (http://3roomlabs.blogspot.sg/2013/04/048b-x-axis-completed.html)
im not an expert on steppers, while testing out a few steppers myself, even though a stepper may be supplied its rated current voltage, it alone is not be able to dissipate heat well. which is why i implemented heatsinks (just some super glue n some cheap china sinks for RAM). i have yet to experience a fail stepper, but my guess is that with a t-case of 50degree-C, the wires inside maybe cooking at 90-100 degree-C. although i find that due to this reason i prefer steppers with higher resistance, most would prefer the lower resistance due to higher torque. and then there is the question of the torque curve vs current supplied, etc etc. in all cases, i would say temperature is the key number to watch (on top of having the drive current adjusted properly), so i would suggest getting something to measure that parameter if you want to know some relative numbers to be sure, well just a hand feel would work too, warm ? too hot to touch? sizzling?
alternatively, you might be interested to look at R-sense mods. to me R-sense mods try to maximise the full use of the current adjust mini trimmer, to try and make the output adjustment more manageable (so that you can physically turn the trimmer more to produce a finer change in current adjusted). the NEMA 14 i have seen in terms of spec are kind of below 0.5A, so my guess is you need a larger R-sense. http://3roomlabs.blogspot.sg/2013/03/rsenser4-experiments.html