Nomad 883 Pro, LED glows if axis moved while off

When the Nomad 883 Pro is turned off, and I move an axis by hand, the spinning of the motors seems to cause the power LED to glow.

I suspect the stepper drivers have flyback diodes that are dissipating the charge back into the power supply, so I am guessing the driver chip’s transistors are not damaged. But without a schematic, I can’t be sure of anything. I am hoping that the maximum amount of power that leaks back is taken into account and won’t damage anything.

If it helps you understand my concern, my 3D printer has also has a small issue with a capacitor retaining charge for too long, as in, you can unplug it, and turn on the switch, and it will actually power up for a split second. Forgetting this during hacking/maintenance is dangerous, perhaps not to the human, but that stored charge might get shorted into something that can’t handle it.

So my next fear is for safety. I’m moving things around while the machine is off, because I am trying to avoid pinching hazard or a rouge spindle. I am not sure how the power switch works on the Pro version of Nomad but if it’s a relay, I don’t want it to latch up accidentally, and then have the machine receive a misinterpreted packet that makes it go crazy.

Trust me, it’s happened on other things before. I’ve had my hand cut up because a quadcopter interpreted a electrical glitch as a command to go full throttle. I don’t think GCODE has checksums to ensure this doesn’t happen.


Is moving the steppers by hand damaging the machine’s circuitry?

Is the circuitry designed in a way that will prevent a unwanted startup?

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Can’t answer your question, but I thank you for asking it in such an intelligent and thoughtful fashion — it’s something which I’ve wondered about in the past, and have been concerned about, and I look forward to an equally thorough answer.

@frank26080115, I also cannot answer your direct questions. But I will point out that it is actually hard to get a stepper motor to turn. As opposed to a DC servo motor, which will have an uncontrolled runaway if the encoder isn’t securely plugged in (I know from first hand…), a stepper motor must receive a timed series of coil winding current and direction changes in order to turn. If one of the two windings is disconnected it will just vibrate in place, even when given a valid pulse train. Just powered up, it locks up static. So steppers are pretty safe from inadvertent movement.

BTW I have a horizontal-axis washing machine with a direct drive (3-phase motor I assume) drum. When I spin the drum with the machine powered down I can get the control panel to light up…


Hi Frank,

While I cant answer the question, There aer various threads discussing what happens if the Nomad is hitting a lot of Switch Limits. Most of them say to move the table and spindle by had to zero. When this is done, the ligh indeed lights up. If this were a safety issue, i think it might have been No-Noed by the Carbide Team…

Just a thought.