Over heating issues... Normal?

Support Motor controllers/drivers and motors
1

Hi,

I just received my Pololu #1208 (10V/500mA) stepper motor and A4988 driver. I’m pretty new to stepper motors, so I am questioning the amount of heat dissipating from both the driver and the motor. I am running 18V to VMot and followed the steps found on this forum in calibrating the current limit. Set the limit to about 350mA. Also running a micro-controller from the 4988 which is jumpered to run 3.3V logic/output.

What’s more strange is that the motor begins to get hot just sitting there not running with reset held low (which I thought would turn off the FETs). Anyway, it is pretty uncomfortable to hold or touch (damn hot), both the motor and driver. Just want to make sure that this is normal before I continue to debug my code. Don’t want to burn up the motor or driver.

I am running in full step mode right now. I am assuming that running half step or greater would cause even more heat. Is that a correct assumption? Lastly, will I get more torque running at these higher step modes or just more accuracy?

UPDATE
My mistake on the part where motor was hot with reset low… Incorrect connection. Motor does not heat up with reset low. The voltage regulator is still pretty hot on the A4988 without the motor running, and only powering up the microcontroller. My microcontroller draws less than 100mA running code.

Thanks!
-John

2

Hello, John.

Do you know how much the motor is heating up? If you have measured the current in the motor coils and confirmed that it is what you set it at, I think you might be seeing a normal temperature rise in the motor. The motor is rated to undergo a maximum temperature rise of 80 degrees C when running at its rated current.

I do not think using microstepping should increase the heat generated. You can find graphs and a table of the phase currents in different step increments on pages 14-17 of the A4988 datasheet. Heat correlates to power, which is proportional to the square of the current (P = I^2 * R), and the sum of the dissipated power in both phases stays the same through all of the step increments.

You will not get any more torque from the motor with microstepping, just more accuracy.

The 3.3 V regulator on the A4988 carrier with voltage regulators is only rated to provide 50 mA of current, and the 5 V regulator is good for 100 mA, so if your microcontroller is drawing a significant fraction of that (or more than that), it would explain the heat.

- Kevin