Nema 8 motor overheating with CNC shield

Hi,

I was hoping to use this motor (rated current 0.2A & resistance 24ohms) with this CNC shield for a Z axis of a pen plotter.

It works well except for the fact that it gets unbelievably hot (was approaching 100°C at idle before I cut power).

I know some heat is to be expected but the other motors (rated current 1.7A & resistance 1.5 Ohms) don't even get warm.

I apologize for my woeful lack of understanding of electronics, but is there anything I can do to mitigate this or is this motor not appropriate for the controller? Turning down the current limit pot made no difference.

Any advice greatly appreciated

Have you adjusted the current limit on the stepper driver to match the 0.2amps of your motor?

...R Stepper Motor Basics Simple Stepper Code

Thanks for the reply!

Yes, turning it all the way down to just before it fails to step the motor seems to save maybe 10 degrees at most

seriouscallersonly: Thanks for the reply!

Yes, turning it all the way down to just before it fails to step the motor seems to save maybe 10 degrees at most

I don't know exactly what stepper driver you have but normally there is a procedure for measuring a voltage that is proportional to the current limit. I don't have much faith in twiddling knobs without a measurement.

PROVIDED you have everything powered off (MOST IMPORTANT) while you connect or disconnect you can connect a multimeter between the driver and one of the motor coils and measure the current while the motor is powered but stationary.

...R

Have you double checked the wiring of the windings for the motor?

Thanks for the advice Robin2, I'll try to measure that when I get home.

MarkT, thanks for the reply. Aside from the heat the motor behaves as expected. Is there any way it could be wired wrong but still respond to steps?

seriouscallersonly: Thanks for the advice Robin2, I'll try to measure that when I get home.

MarkT, thanks for the reply. Aside from the heat the motor behaves as expected. Is there any way it could be wired wrong but still respond to steps?

That type motor is designed to be mounted in metal which is used as a heat sink to cool the motor. How do you have it mounted? A picture, please.

Paul

Well it won’t take a photo for me to tell you it isn’t mounted to metal but here’s one anyway!

I had a feeling this was part of the problem but I didn’t think it would solely account for the temps I was seeing. Annoyingly I can’t find any metal brackets for these motors so I 3D printed my own. Do you think some heat sinks would work or do I need to find a way to mount it to the aluminium?

I’m also considering switching it out for a pancake nema 17 but wanted to keep the weight of the assembly as low as poss.

Please note everything else in the photo is rough prototype

Thanks!

If that stepper is just turning a leadscrew, you could use almost any little stepper to do that. Plastic does not conduct heat very well.

Learn to fabricate aluminum. You could make a plate to go between the plastic mount and the motor and fold the edges up and around the motor to conduct the heat away.

But, I really think you are running the motor with too much current.

Does your motor need to hold the leadscrew in position, or will your pen stay where you put it?

Paul

Paul_KD7HB: But, I really think you are running the motor with too much current.

@seriouscallersonly, you need to adjust the current setting using appropriate measurements.

All you have done so far is twiddle the pot with a screwdriver. A small twitch of one's fingers could change it from 100mA (too low) to 400mA (much too high),

...R