dannem
1
Hi. Did finish bulding my geeetech i3 today. Haven got it running yet cause i did something wrong i guess since it says min temp or something like that. Anyway, i accidentally pushed the extruder away quickly and my fans, and 2560 and the display lit up for haft a second. Seems wrong to me? It was disconnected from usb and ac. Any idea?
jfield
2
Yes, on my printer that happens when I move the plate. Has never hurt my board though. Sounds like maybe your t/c is wired backward, or a firmware setting is wrong. Need more info on the error you are getting and someone will be able to help you.
Same thing on my i3. Moving the x or y axis will briefly power the board. A stepper motor can actually be used as a generator, so everything is functioning as it should. As jfield said, check the thermocouple wiring. It’s probably a bad connection that causes bad temp reading and gives the min temp error.
Yes, stepper motors can act as generators, so if you move them by hand they will generate voltage, and power up the electronics. If you move to motors slowly usually its not causing any issues or damage to the electronics, so its “normal”.
For the mintemp error part i have already replied in your original “New 3d printer reprap mk2?” thread.
https://www.3dhubs.com/talk/thread/new-3d-printer-reprap-mk2
T.
cobnut
5
Happens on my FF Pro when you push the bed down as well. Weird, but normal; motors and generators are very close cousins 
I’ve got an HE3D (Prusa i3 clone) that does the same thing if you move any of the steppers when it has no power to the board. It seems the steppers will generate just a little bit of DC voltage that backflows and lights the display just a little and can even flicker the LEDs on the board.
I’ve played around with it but haven’t noticed anything harmful, and everything works fine when powered up again. I’m not an electrical engineer so I don’t know exactly why or what is going on, but that part about power being generated I have seen too and can confirm.
Miro
7
It’s normal, steppers like any electro motor will generate power when rotated manually.
