On my A1 mini, the extruder stepper is often burning hot at the end of prints, is it normal ? And does it reduce life expectancy of printer ?
If yes, has anyone made a Mod to cool it off ?
Note: The stepper from another A1 mini from a friend also exhibit the same behaviour
Steppers can get quite hot. They’re designed for it. It’s the nature of how they work. Even when the motor isn’t turning, it still has full current flowing through it.
I don’t own an A1 so I can’t say. But if it’s exposed so you can touch it, it shouldn’t get hotter than 70ºC. Safety certifications like UL require anything hotter to be shrouded so you can’t touch it, or to bear a big yellow sticker saying “Caution Hot Surface” or something similar.
If you can put your hand on it and keep it there for more than 5 seconds, it’s not that hot… 
I don’t know how hot it is exactly but you can’t touch it for more than a second. Worries me as well. Never had stepper motors that got so hot on a printer.
But I guess (or hope) they tested those temps.
Power can be loosely defined as “work done over a fixed period of time”. And Power = Heat.
Get the same amount of work done in half the time, that’s twice the Power.
The printer’s high acceleration and the speed that enables requires more Power, the motors work harder, and that means they get hotter.
I am in no way an expert in the matter,
but I believe the general relationship is not that simple since unlike DC motors where to increase speed, you just increase current, steppers rely on the switching of power in multiples coils, so most of the losses are not caused by the frequency of the change, but by the typical magnetic losses
here a graph illustrating my thinking
But still, the problem is not really to know that indeed the stepper rapid change may cause slightly more heating (may be also due to the increase of impedence in the stepper coils or a higher drive current to compensate for the speed), but if bambulab really intended for it to go that far, without slow degredation in lifespan
unlike DC motors where to increase speed, you just increase current
In any motor be it stepper, brushed, brushless DC, or an AC motor, speed is proportional to voltage and is defined by the motor constant “KV”. It’s motor torque that’s proportional to current, and it’s constant is called “KT”.
KV and KT share an inverse relationship. A motor with higher KV will spin faster for a given voltage, but produce less torque for a given current. A motor with a lower KV will spin slower for a given voltage, but produce more torque for a given current.
Motor size does not directly dictate these parameters. A small motor and a large motor with the same KV will have the same KT and their RPM/volt and the torque they generate for the current they’re passing will also be the same. The only difference is that a smaller motor is wound with smaller wires that have a lower maximum current carrying capability. So as you increase voltage and current, at some point the smaller motor will burn out while the larger motor continues to perform because its windings can take the Watts (and also because, being bigger it has more surface area to dissipate heat).
Yes, I grossly oversimplified my explanation since going in to detailed motor theory doesn’t really benefit the discussion. The key takeaway is that steppers in a BBL printer run hotter than the steppers in any older generation printer because the BBL printer is running faster, doing more work per unit time. The rate of heat dissipation is unchanged, but the rate of heat generation is higher, so parts get hotter as a result of all the extra work they’re doing.
But we were talking about the extruder and the extruder does not necessarily go faster than „old“ machines every time you print because you are still limited by the max flowrate of the hotend/filament. So if I print a vase in „Generic PETG“ (8mm³/s) with thick line width, the printer does not necessarily go faster than any old printer with an volcano style hotend. But it sure has a smaller motor so a direct comparison is not easy.
But maybe my thought process is wrong. I guess we will see down the road if the lifetime of the steppers is impacted by the high temperatures.
PS: The discussion reminds me of Apple and their cooling approach on Intel MacBooks. They let them run way hotter before they let the fans ramp up than any other Windows laptop I know of. And everyone said it would impact their lifespan but my 2013 Retina Macbook runs fine till this day. And it had to survive many rendering sessions where I would always wonder why the fans are not ramping up sooner, haha. It was not a beefed up version though, just an entry level machine.
That’s your answer, right there. If the motor is doing the same amount of work but it’s smaller, it will be hotter simply because there’s less surface area to dissipate heat.
I’ve seen some models on Makerworld that allow you to put a fan