A question: how hot does your Prusa i3 MK3 extruder stepper get?
Hi guys – I’ve been reading around, and it seems that perhaps my extruder stepper isn’t unusually hot for an Original Prusa i3 MK3, but I’m just seeking reassurance.
So, running ASA at 255C, 100C bed and an enclosure, the stepper gets hot enough that I can only hold my finger on it for a couple of seconds before that becomes too painful.
Is that really par for the course?
The filament path is clear (undoing the extruder to release the hobbed nut means I can push the filament through the hot nozzle with the usual level of resistance).
The stepper spins with my finger, so it’s fine.
The free hobbed nut spins fine.
It prints fine.
But it’s damn hot. 100mm/s target speed, no slowdown for infill, the usual retraction settings, 255C/100C, ASA. It’s still hot without the enclosure.
I don’t have a mk3, but the enclosure would cause an increase in temp, I have a mk2 clone and the E motor does get hot but never, that HOT!.. Although I don’t have mine in an enclosure. I have never had any motor get that hot… Maybe I’m not pushing them hard enough?
@Jeremiah_Coley I have a MK2S and a MK3 and the MK2S extruder stepper doesn’t get any more than warm in the same conditions. The MK3 stepper gets really hot even when not in the enclosure.
I know the steppers are driven by very different drivers on the MK3 (Trinamic, fancy current sensing, etc.) but I’m still surprised at the extent of the difference.
hmm I don’t have prusa machine but I ran mine overnight sometime and occasionally I would touch the extruder motor just to feel how hot it gets. mine never get hot enough that it is painful to touch… I’m also running 24v with trinamic
A stepper motor run at its rated current and rated ambient temperature WILL be too hot to comfortably touch. They’re supposed to run very hot, and if they’re NOT hot, you’re giving up a lot of torque.
This is a common point of confusion. For DC motors you may be used to, load=heat and overloading the motor will overheat and damage it. But for steppers, torque capacity = heat, you absolutely cannot damage them through overload, and they actually run cooler the faster they spin.
Many people deliberately run steppers well below rated current to keep them cooler, which is fine if you want to do that, but you’re giving up some motion crispness and safety factor on nozzle collisions and the like when you do that.
The driver makes very little difference to motor heat (on 12-24v systems anyway), it’s almost entirely a matter of drive current and thus torque. Printed motor brackets are a good reason to dial down motor current and run them cool.
@Mark_Wheadon It’s minor and is reversible at any normal running temp (eg up to 120C coil insulation rating). Not something you need to worry about. They’re not neodymium magnets.
Hybrid steppers get very little torque from the permanent magnet in any case – the rotor’s permanent magnet is just there to bias the electromagnetic flux in a particular direction through the rotor. Then the coil electromagnet fields produce a reluctance torque effect through the rotor/stator teeth gaps, not any kind of “electromagnet attracting/repelling a permanent magnet” type effect you get in a normal DC motor.
