GLCD lighting up with no power on

K40 omtech machine with C3D laser board and GLCD screen running smoothie and lightburn.

I just noticed a very odd thing with the GLCD. By moving the focal head by hand, and no power to the machine (unplugged) the GLCD will light up.

The faster I move the head, the brighter the screen lights up.

How and Why does this happen?

I even unplugged the power cord to the laser board. It made no difference.

I had to link a sample video to show what it does.
https://imgur.com/a/Gttzla0

An electric motor can also be used as a generator. This is especially true for stepper motors. What’s going on is the motors are generating a current, which charges the buffer capacitors for the stepper drivers. Those in turn power the 5V and 3V regulators on the board, which lights up the LCD.

Sorry I didn’t see your reply. I didn’t get an email notification of it. Thank you for the explanation as to why the screen lights up. I had never noticed it before. I’ll be careful to not move it fast so I don’t risk burning anything up.

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