Ender3v2 octoprint USB 5v problem?

  • Hi, do I need to cut the 5v cable when connecting a Raspberry Pi to USB to run Octoprint? Will I fry the Pi or the motherboard if I dont cut it?

  • @JohanL
    Ok great to hear, yep, that should work!
    Did you try to extrude or retract manually from the Control tab, watch if wheel moves? (Heat up nozzle first)
    Or try other movements. It's weird that only extruder is affected. Maybe you hit a wire loose...?

  • Thanks, I just carfully cut open the cable, cut the red wire, pulled it out of the shield on the outer sheth and taped it so it could not short to the shield. Connected the cable to a mobile phone and confirmed it did not charge anymore. If it had not, I guess I had cut the wrong wire. Then connected. Now everything is working fine! (I did have some spare USB cables in case I'd cut the wrong cable ;))

    Except that my extruder seem to have clogged, or can the settings have been messed up? I did install the temp fix, but temp on display and in octoprint shows the same and it still seem to have trouble extruding the first layer...

  • @JohanL I have no idea in which cases it is needed. You and others are welcome to check it out further, but personally, I found it easier and safer to just do the modification, rather than try to find out definitively if it is needed or not. Even if somebody had come with convincing evidence that it is safe without, I didn't feel it was worth betting my printer on.

    There is no negative impact of doing it. All the cable needs to do is transfer data between pi and printer, which works perfectly without the 5v line.

    Yes, there are various ways of disconnecting the 5v. The best way is one that fully stops 5v and that you are comfortable with.

    I decided another way worked best for me:
    I got one of these micro USB ports, cut an existing USB cable (so only keep micro USB plug and half a cable), and only soldered 3 out of the 4 wires to it. Then I hook up that up to the pi with another standard/unmodified cable, which I can replace easily if I want a different length.

    For my option, you need to be able to do some basic soldering, and I would suggest to use a multimeter to confirm 100% which cable is which. For example after you cut it, check which colour of wire is connected to each contact inside the big USB plug using continuity function. These are handy skills to have as a hobbyist, and will serve you over and over again if you learn + invest in some basic tools. (People reading have different skill levels so this is not directed at you in particular)

    Simply cutting a wire should work too, just be careful. Don't cut other wires, and tape/insulate it good when you're done. There may well be an established colour convention, but I don't trust anybody. So if I was using that option, I would also do a multimeter confirmation like above, rather than assume red is 5v for that particular cable. Maybe it's being overly cautious, but I don't care. If a cable manufacturer wired my cable differently, at least I won't add to the threads of fried printers.

  • @JohanL Like I said, I don't know what kind of fault mode would cause such damage.

    The 5Volt supply from a computer or a Pi will be current limited. So if the printer simply 'smokes' when 5V is applied via the USB connection, that would suggest a wiring or assembly problem in the printer.

    However, if a powered printer is connected to an un-powered computer, resulting in the printer 'smoking' that would suggest a design fault where the printer supply is not adequately protected.

    Another possibility might be a more serious problem where the common/0V/chassis is sitting at an AC or DC voltage higher than the computer. That could 'smoke' the printer, and would potentially be a Health & Safety issue. ...but I really don't know because I haven't had these problems.

    I couldn't find a commercial USB cable with +5V disconnected either, so that's why I just butchered one of my existing data cables. As you will see from my blog post, I did not completely cut the cable, just the 5V core, so I think the end result is quite robust and easily recognisable. I don't move the printer around, so yes, its the 'best' way for me.

    The reason that 'host machines' make 5Volts available via the USB posts, is primarily so that they can power up simple devices, such as memory cards/sticks. My Creality printer (and probably yours also) does not have a true 'plug and play' USB port. It has a USB to serial module running at a relatively low data rate (on mine its 115,200 Baud).

    Therefore I can't think that it is much use for anything other than being controlled via computer (Pi) using specialised software. So the answer is No, the 5V line is not used for anything else in this application. (However, by simply cutting an external cable you have not modified the machine internals).

  • OK, thanks, I do not like to smoke either printer or Pi (printer from Bangood, so warranty is questionable, Pi is out of warranty...)

    So what you are saying, probably, this is a defect from Creality on some boards? Sad they did not go out to inform which boards/models that are affected. 😞 It "should" work, but does not always? And the voltage do not necessary be high all the time, so measuring does not make it safe to conclude it is OK?

    So, is slicing the USB cable open and cut the red cable the "best" way? Seems also be some USB adapters that do this, but not that easy to buy, the ones with availability is doing the opposite (cutting the data, keeping the power). I have seen tape on the connector that seems like the easiest way, but feels not that robust? Will everyting else work out if I cut the 5V, or is it used for something?

  • Make that 2. I've no idea why a printer should 'smoke' when the USB is connected to a computer, but I didn't like the idea of my CR-10-V3 screen lighting-up when powered off but connected to a running pc. So this is what I did: http://captainbodgit.blogspot.com/2021/05/3d-printer-isolating-usb-5volt-feed.html

    I'm equally unhappy that when the bed is moved with the power turned off, there is enough back-emf generated to light-up the display: https://forum.creality.com/topic/1930/moving-platform-by-hand-lights-up-controller-display

  • @JohanL well if this forum is of any indication, see how many results there are:
    https://forum.creality.com/search?term=fried usb&in=titlesposts

    If i can be 1 voice from the other group:
    Whether necessary or not, I did disconnect the 5v of the USB cable to my ender-6.
    Everything works fine and nothing has fried yet.

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