Stepper motors getting HOT!

What I'm saying is that I see .24 amps on one of the leads, regardless of how low I set the current limit. Even if I set it to half of the .16 limit, I still see the .24 amps. And I see that when the motor isn't moving.

So that's not right, is it? And I have several of the A4988 drivers, it isn't a defective driver.

I need the motors to run much cooler because they are in plastic housings that will melt if they get as hot as they can. So it isn't enough for me to run them below their rated max temp. I need them to run as cool as the old controller can run them at.

With a chopping motor driver, you cannot accurately measure the winding current using a multimeter. If you have the Pololu boards, follow the instructions for setting the winding current provided by Pololu.

Thanks, but I did follow the instructions and the motors are running very hot. Any suggestions as to how to get them to run cool like the other controller does would be appreciated! If it would pro ice any useful clues, I could hook up an oscilloscope...

Simply reduce the winding current, as per instructions.
Industrial stepper motors are designed to safely run hot at maximum output. Yours is rated for 80 degrees C maximum temperature rise.

Thanks, but as I said, I need them to run much cooler than the max they can take. That would melt the plastic case they are in. I need to understand how the other controller is running the motor at such a cooler temp than the A4988s do, and then either adjust the a4988s go tun that cool ( which isn't looking possible) or get motor controllers that can run cooler.

I will repeat myself.

Simply reduce the winding current, as per instructions.

If you reduce the current, the motors will run cooler. Why is this so difficult for you?

jremington - I really appreciate your help, but I'm not sure if you didn't read my original post all the way through, or maybe it wasn't clear. I did adjust the current down as per the A4988 instructions. I'm turning the trimpot counter-clockwise to limit the current, and going by the voltage at the REF pin on the driver - as per the instructions.

I even tried adjusting it down to next to nothing - to 1/4 of the rated current - well past the point where the motor won't even respond to step commands, and the motor is still getting too hot.

And now, just for grins, I turned the trimpot all the way down, setting the current limit to 0, and after 10 minutes the motor was at 80c. When I run it with the old controller, it doesn't get hotter than 32c.

The controller my controller is replacing can run these motors much cooler, and I need to too.

That is what I don't understand and need help with. Is this a feature of the chopping drivers I'm using? Is something else going wrong?

Sorry, I did not read your post carefully enough. However, typos leading to errors of a factor of 1000, like this one are discouraging:

down to .015 volts, which should give me a max current of .027mA

Your driver may be broken. Contact Pololu instead of this forum.

Yes, sorry - I meant amps, not milliamps. It happens. But as I also said, I have several of these A4988s. I tried swapping them out with brand new ones. Same results.

Then your wiring is probably wrong. Post a schematic and a clear photo of the setup.

Update on this. I figured it out. So, to clarify, my controller connects to the robot over a DB25 connector. Power goes into the robot and is fed to the controller over the DB25. The leads to all the motors are from the controller back out the DB25 to the robot.

The issue with the steppers is that there is 24V being sent to the steppers, unregulated. There is a raw 24V line from the DB25 back to the robot. I never knew what that was for, so just had my controller wired to send it as well. It seems that it's going to one or more leads of each stepper. When I break that connection, my controller can control the steppers no problem, without overheating, but the original controller that came with the robot can only "twitch" the steppers.

So somehow that power is needed for the way the original controller controls the motors.

Any idea what is going on? Why send unregulated power to a stepper motor? (By "unregulated", I mean that it is constant, not modified during the sending of individual step commands to the steppers.)

It is difficult to make sense out of your post without a schematic.

Sorry. It is a fairly complex circuit - 4 DC motor controllers, 2 stepper motor controllers, everything in/out of a DB25, a few sensors, a speaker, a switching voltage regulator... Not sure you'd want to go through all that!

The gist of it is that there is power applied to the steppers that's constant, and independent of the control (step) signals. I didn't build the robot, and don't know what it does. It seems to be some way of controlling a stepper that I don't know about. If that's enough for you to go on, please let me know what you think. Otherwise, I understand.

I realize this is an old thread.....but it is still a hot topic. And continues to be viewed.
I do an awful lot of 3D printing and regardless, heat is not a friend of electric motors.
During printing the motors can get quite hot.
Eventually it can change their electrical characteristics, damage insulation etc.
As 3D printer stepper motors get old, the internal resistance increases.....and given enough heat at the wrong time during a print can cause the motor to miss steps or even stop working. The result will be a failed print. I find my prints to be more consistent and precise when the stepper motors are heatsink cooled.

Here's how I keep my stepper motors cool during long and taxing prints.
There's all shapes and sizes of heatsinks available on ebay. In some tight spaces I use a cluster of small heatsinks. Whatever works. I try to cover as much of the metal surface as I can with heat sinks.
Just make sure to move all axis to their extents before printing to make sure there's no interference.
Of course, they are all attached with heat conductive thermal paste. NOT sticky "thermal" tape.

A Laser Thermometer clearly shows the results and the motors will also last longer.

Many higher power drivers like those using Toshiba 6560 chips have a standby feature that cuts current down 50% or more to reduce standstill power consumption and heat.

outsider:
Many higher power drivers like those using Toshiba 6560 chips have a standby feature that cuts current down 50% or more to reduce standstill power consumption and heat.

That's great (when available). Many 3D printers don't have that protection. Mine simply resulted in failed prints when the motor got too hot.

Also, if you adequately cool the motors, you should be able to avoid thermal problems completely.

I was running into problems with prints at temps as low as 140F

A LOT of 3D printers out there are somewhat "cheap" builds and the motors aren't top of the line.
I have several very good quality 3D printers and even those are the ones I've had thermal problems with.

But as you suggested, it varies. Heatsinks work for me. Others mileage may vary.

quamikazee:
As 3D printer stepper motors get old, the internal resistance increases

No, the properties of copper windings do not vary like this(*). Temperature affects the internal resistance
moderately, age does not.

What can happen in an overheating motor is the permanent magnets lose their strength
permanently.

(*) http://ieeexplore.ieee.org/document/7409186/

If you are using the a4988 at full-step mode (sleep pin connected directly to the reset one), the maximum current allowed will only be 70 per cent of the current you regulated with the trimpot.

Pedro-Castelani:
If you are using the a4988 at full-step mode (sleep pin connected directly to the reset one), the maximum current allowed will only be 70 per cent of the current you regulated with the trimpot.

Which is exactly what you want, since the current you set is the quadrature amplitude of the current phasor.
As the current phasor is constant, the total power dissipation in the motor windings summed together is
constant, whatever microstepping and whatever position, for a given setting of the reference signal.

Ia^2 + Ib^2 = Inominal^2

In full stepping mode the A4988 uses quadrature angles 45/135/225/315 degrees, so that
Ia^2 = Ib^2 = 0.5 x Inominal^2

Or pit another way the motor will run just as hot whatever microstepping setting or position for
a fixed reference voltage.