Overextrusion when bed is heating

  • Hey everyone!

    I have an Ender 3 that I keep modding until stuff breaks (and yet, I keep doing it). So far, I've been able to solve every issue, but this is a new one.
    I'm just waiting for a few more parts (E3D V6 Hotend and Thermistor) before I fully upgrade this printer to use the Duet Wifi.

    Anyways, I'm still running the stock mainboard with TL-Smoothers, and I'm having a very very odd issue. Just recently I bought a magnetic heatbed, just like on the prusa.
    Since I changed the stock ender heatbed (which was terribly warped anyways) to this one, I'm getting over extrusion exactly when the heatbed is heating. Also, while print-moves are generally very quiet as I'm also using stepper dampeners, as soon as the heatbed heats, there's also a very audible vibration, presumably from the X stepper.

    This is what prints look like since the swap of the heatbed:

    Since the lines of over extrusion are not in the same spot, and since my z-axis is definitely not binding, I'm concluding that this is not an issue with my z-axis.

    I also took a video that shows that the over extrusion and vibration happens EXACTLY when the heatbed is ON.


    Whats going on here? Is the PSU too weak for the new heatbed? Is it maybe generating some kind of inductance or interference that messes with the drivers or microcontroller? I'm seriously baffled how these two correlate to another. Maybe an experienced user has run into this before?
    I also just printed a cube with the heatbed off. This confirms that it is caused by the heatbed.



    Edit: I'd like to mention that I'm using Marlin 1.1.9 and currently, the bed is running in bang-bang.
    I had PID control for the bed enabled for 2 days, and everything printed fine and temperatures were much more stable - BUT, I was getting a really wierd clicking noise from the mainboard area when the bed was PIDing (turning on/off very frequently) and the x-motor was vibrating at exactly that clicking and on/off rate too... But the bed is controlled by a mosfet. How can anything click there?

  • @devleon Just to be clear. You are running a stock main board on an Ender 3 printer, and Marlin 1.1.9.Firmware yes? Not a Duet board nor RepRap firmware?

  • @deckingman Yes, stock so far with highly modified Marlin 1.1.9. But as soon as the E3D V6 is here, I will be switching over to the Duet.

    I'm thinking this is a power delivery problem, as in the cheap NoName 300W PSU included with the Ender 3 is probably failing to deliver enough power and that's maybe what causes some missed steps for the X Stepper? Could explain the noise and over extrusion since it stays at some points longer.

    I measured the new heatbed at 3 Ohms, which means at 24V it will draw 8A and 192W.
    If the cheap noname PSU can only output about 250W, that's a pretty close call with the 40W heat cartridge, 192W heatbed, stepper drivers and some 24V LEDs.

    But I'm not 100% sure, that's why I'm asking.

    I'm thinking of buying the MeanWell LRS-350-24 anyways though, I don't want to trust this cheap noname PSU. Would that be a good choice?

  • Moderator

    @devleon said in Overextrusion when bed is heating:

    the bed is running in bang-bang.

    Your pictures look exactly like what I'd expect from a flexing bed heater in bang bang mode.

    I think it's time to upgrade to the Duet. 😉

  • @phaedrux said in Overextrusion when bed is heating:

    Your pictures look exactly like what I'd expect from a flexing bed heater in bang bang mode.

    Can you elaborate what you mean by flexing bed heater? In Marlin I already lowered the BED_CHECK_INTERVAL to 500ms, and the temperature is oscillating by maybe 1 degree at the very beginning.

    @phaedrux said in Overextrusion when bed is heating:

    I think it's time to upgrade to the Duet. 😉

    Everything already prepared. Just waiting for the E3D to arrive 😄
    Still, I just wanted to make sure I won't have the same problem after I upgrade to the Duet.

    So, I have ordered the MeanWell LRS-350-24. Will that fix it, or is the problem somewhere else?

  • Moderator

    With bang bang mode the heater basically flips from full on to full off, like a light switch. The high heat followed by rapid cooling coupled to a flexible PCB and probably less than ideal 4 point mount causes the bed to flex up and down a surprisingly large amount.

    You can see it in action here: https://www.reddit.com/r/3Dprinting/comments/8uz9vg/bed_deflection_with_bang_bang_control_method/

    And you see it in action on the walls of your print. The print is literally lifted closer to the nozzle when the heater comes on. When you consider the layer height is only 0.2mm it doesn't take much.

    You even fixed it yourself by switching to PID mode which smoothes out the heating cycle by rapidly flipping on and off. The clicking you heard if likely due to the cheap quality of components.

    See here for guidelines on choosing a power supply: https://duet3d.dozuki.com/Wiki/Choosing_the_power_supply

  • Thanks for the detailed explanation! I had no idea it could flex that much, just because of the heat.

    It was definitely better with PID. I'm going to wait for the new PSU and re-enable PID for the bed then. And upgrade to the Duet as soon as possible 🙂

  • Just wanted to add that after I had posted this issue on /r/3dprinting, a couple other people mentioned that this issue did not go away after upgrading to the meanwell psu.
    Some people with an ender 3 pro (that has the meanwell psu) also have the same issue. This makes me to believe that this is simply an issue with the cheap ender 3 mainboard.

    Why the noise is only on the X-Axis is unclear, but people that switched the X and Y connections had the noise and vibrations also switch to the the Y-Axis, so it has to do something with the X-Axis driver.

    Anyways, I'll update this once I have converted to the Duet. For now I'll simply try to print with the bed off, or enable PID again, even if that noise and vibration will drive me insane...

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