Killing a stepper driver

jens55

It is well known (and specifically warned against in the documentation) that plugging or unplugging a stepper motor should only be done when the controller is off. I am curious about the failure mechanism. What actually happens? There is a connector with 4 pins, two of them may be energized. What is different when I plug / unplug things compared to when the controller turns a winding on or turns it off?
I would ask that you only comment if you actually know what is happening and not just guessing at the reason.

gloomyandy

@jens55 It may not be as big a problem as people think... https://www.youtube.com/watch?v=uyWolKFzb-A

Certainly when you unplug the cable you may get a discharge and spark from the collapsing magnetic field in the motor. As to possible damage this probably comes down to how well the driver/board has been designed. See: https://electronics.stackexchange.com/questions/345003/why-does-disconnecting-a-stepper-motor-while-powered-on-damage-the-driver

I guess it depends if you are feeling lucky.

dc42

@jens55 Duets are fairly tolerant of connecting/disconnecting motors when powered, although you should always avoid doing it.

The easiest way to kill a stepper driver is to connect the stepper motor wires to the wrong pins on the Duet. The drivers assume that the two pins of each phase output connect to one phase of the motor. If you connect the two wires of a motor phase to the outputs of different phases from the driver, then the driver can't regulate the current to the motor. If you are lucky then the driver short circuit protection may kick in before the output mosfets are destroyed.

jens55

@dc42 thanks, that makes sense. Although if you plug in the wires the wrong way around, I would think that you would still kill the driver independent on if you do that while things are powered up or not. The driver would fry as soon as you turn on power and activate the driver if it can't regulate current.
I had not thought about the current regulation aspect.

jens55

@gloomyandy, thanks for the link to the stackexchange site! Very informative.

gloomyandy

@jens55 Did you watch the video link? Surprising what you find sometimes!

jens55

@gloomyandy he tried so hard ....

oliof

@jens55 the one way I managed to fry a stepper and driver was sending 1.5a to a 0.4a rated stepper I had mixed up the phases on and tried three times to make the error message go away by just rebooting the Duet2 board.

Luckily, @PCR was able to swap out the TMC2660 and the board is in perfect working order. The stepper did not survive the ordeal.

oliof

@KenW ants? Crazy story I love it!