I have been running my i3 MK3 for about 12 hours now and the motor on the extruder is fairly hot, not too hot to touch but I'd guess its about 60c on the outside. Is this within normal operating temperatures or should I let it cool down before starting more prints?
The maximum operating temperature can be found in the specifications of your steppers. Usually the ambient temperature operating conditions are limited to 50 °C with a maximum operating temperature in the range of 70 - 100 °C. For instance, the steppers I use are limited to a temperature of 80 °C. It is however advised to keep this temperature lower, e.g. to max. 60 °C to prolong the life. Do note that very high temperatures could be a problem for "self-printed" stepper mounts of the wrong material (materials with a low glass transition temperature).
To answer your question: "Yes, steppers may get hot, but if you want them to get too hot is up to the mounting system and how long you want to use them."
While such temperatures may be OK for extruder motor itself (and probably for extruder body, since it is printed in PETG/ABS), but it can be dangerous for the filament that you are using to print your models. Heat from extruder motor can creep through shaft to Bondtech gears and start to pre-melt filament.
60 °C is enough to soften PLA. Your filament may warp or melt just above heatsink, jamming, and clogging the extruder body.
What you can try to do:
- Open or remove enclosure;
- Glue a generic heatsink on your extruder motor with some thermally conductive adhesive or epoxy;
- Add an active cooling fan for your extruder motor (or for heatsink of your extruder motor). You can power it from Prusa PSU (then you will need 24 V fan), or plug additional PSU for fans and lighting;
- Upgrade extruder motor to LDO / Moons motor. These run about 10 °C cooler than stock extruder motor;
- Upgrade to Bondtech extruder. Bondtech extruder features 3:1 gearing ratio, and can be run with lower current (e.g. less heat). Also Bondtech extruder uses plastic gears, so heat can no longer easily move from extruder motor to filament.
50 °C feels very warm, 60 °C feels hot, 80 °C is painful.
I measured the temperature of the steppers on a Prusa mk3last week. They were all around 45..50 °C, except the extruder stepper which runs around 55..57 °C.
The temperature is stable like that. Letting them cool down is useless, because they would quickly go back to these temperatures after starting the next print. Stepper motors tend to dissipate more power when they stopped or slow compared to when they run fast.
I would not worry about it.