Z probe starts to trigger continuously after hotend fan running

  • Hi at all,

    I have a Kossel XL Plus and the z probe on the Smart effector was just working fine until last week. On Thursday I removed it from the delta rods to lubricate the extruder. Afterwards, when I started some print jobs, the automatic delta calibration failed two times that evening with incredible high deviations and the hotend crashed into the frame of the printer outside the hot bed.
    On Saturday I tried to collect more information about the error from Thursday and I recognized the following:
    When the hot end freshly heats up everything works normal. After it is staying hot (at 220 degrees in my case) for some time the z probe starts triggering randomly from time to time. This becomes more and more until after a few minutes it is just continuously triggering without pausing to trigger any more. When I turn the hot end off it continuous to permanently trigger even when the fan slows down at very low temperatures. In the moment when the fan completely powers off at 45 degrees the z probe stops triggering immediately.

    I have no explanation for this behaviour. First of all I didn't change anything on my setup when this error started to happen and what is more I would expect an electric interference to start with the hot end fan and not to become stronger with time. And if this would be a purely mechanical issue it should change when the fan slows down and also if I hold the hotend fan in my hand, which shows no significant difference.

    Has anyone an explanation what could cause this strange behaviour and how I can further analyse the source of the error?



  • Dj had this issue from the very beginning. The fix it to move the fan away from the hotend.

  • Did you happen to remove any of rods when you did this? I ask because I was able to stop my probe from triggering by changing the polarity to N and S in the arms at adjacent mag balls. Maybe the poles got changed?

  • It definitely helps the fans to spin properly if the poles alternate on the rods. But the constant triggering of the strain gauge was in my case caused by too close proximity to the uprated sunon fan I was using, inducing current. I just moved the fan further away, then later installed water cooling.

  • Thanks for your answers.
    I did not remove the rods from the printer, just from the Smart effector. I never thought about which polarity they have, but since they are in the same order and direction as before, I would expect the polarity to be also the same as it was when it was still working.
    @ Dj and number40fan, until Wednesday everything was fine with my fan and I did not exchange it, move it or did something else with it on Thursday. So it should have shown the same behaviour before. And also it seems to be strange for me that some interference with the fan would take such a long time to slowly build up when the fan is running, does not change when the fan slows down but then immediately stops when the fan stops.
    Shouldn't an interference with the fan show effects which directly correspond with the speed of the fan?

  • administrators

    Is it possible that your effector has developed a temperature-related fault, so that the issue occurs when the effector has warmed up due to heat from the hot end?

  • I tested a relation to temperature changes by disconnecting the hotend fan while the z probe was triggering at 220 degrees. But the z probe stopped to trigger immediately.
    After I let it cool down again I saw a little "nugget" of dust at the outer side of the fan which was not standing out of the fan before. When I pulled it out some fine fibres (thin like a hair) of plastic followed the dust nugget. It looked like the fan had sucked in some plastic fibres from stringy prints and they combined with normal dust to build up this nugget.
    After removing the nugget I had an idea and tested the z probe again. It was working fine again.
    My theory is that the dust nugget slid between the fan blades and the housing while I removed the smart effector from the printer. Afterwards it slowed down the fan and somehow, since it had to work harder, it maybe heated up internally, leading to stronger magnetic fields emitted (I have no idea if that is nonsense or possible) which influenced the z probe. This would be an explanation why the effect was slowly building up but immediately stopping when the fan was stopped.
    So my problem is solved now and I hope this thread will be helpful to others running into this issue.
    Thank you for your answers. 🙂

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