Stepper motor overheating question

  • The stepper motor drivers have some overheating protection I assume. But is there any protection of the stepper motor from overheating? For example, if I connect a motor that is rated for 0.5A, but the duet is configured for 1A, then the motor will overheat quickly - is there any protection or detection of that?

    My initial thinking is "definitely not" and that the motor will fry itself and cause some kind of short/fire and the duet will die from the short or the fire. But sometimes I ask questions here and am surprised by the answer.

  • The duet has no way of knowing the temp of the motor. You could add a thermistor I suppose.

    Stepper motors have a fairly high operating Temp, and can handle quite a bit, but double rated current is pretty extreme.

  • What happens exactly when it gradually overheats? The insulation on the electromagnet wires melt, then it shorts, then the board fries? Or do you think the driver will detect the short and protect the board?

  • Insulation will degrade gradually, but ultimately the short will be more sudden when insulation breaks down completely. Demagnetizing will be gradual, and could be (to some extent) temporary up to the point where you go past the curie temperature. But most motors are rated for 100C and some up to 150C so unless you have metal frame for mounting the plastic parts will give in first.

    Some of the boards have fuses and/or short circuit protection in the drivers, but I don't think I would gamble a $200-ish board for a $20-ish motor.

  • I had a cheap Chinese motor die on me during the first hour of printing. It went sort of OK during the first test print, but as soon as the motors were powered up again for the next print the machine would spam me with "short to ground on driver N" messages. I took out the motor to test it and, yes, it was shorted between all wires alright. The motor was running at 2.4A at 24V, so I suppose it's reasonably protected given that you've installed enough cooling for the drivers to dissipate an odd power peak.

  • Interesting


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