Interesting that you just wrote about this issue, I saw it only after spending a couple of hours trouble shooting serial timeout issues between a newly setup Octopi and old refurbished 3D printer.
Beside the backwards powering, there is an issue of voltage / level differences if devices are not grounded properly or are running of different power sources.
In my case, I removed the printer PSU from the printer it self, to house it external. With that the grounding of the metal parts of the printer it self was removed. I havent thought much of it at the time of doing it - its all just low voltage @ 24V that feeds the motherboard etc !?
Well the USB chassis is in contact among other PCB parts with the printers ground - but not mains supply ground !
I was measuring up to 80VAC differential, that somehow travelled to the Raspi, from there I was able to measure the same different from Raspi ground to mains ground.
Now one more curious thing was, that 2 out of 3 USB-A to USB-mini had shield not connected from one end to the other, even worse the cheap wall wart I used to power the Raspi was floating without ground connection to shield components or GND of the PSU.
Wiring / Grounding everything properly, replacing bad USB cables and using a more decent Raspi PSU solved the serial time-out / drop out issues so far (fingers crossed).
It seems some Raspi models / iterations are more prone then others, even within the same model series.
It does work - maybe not in your ideal world, but technically it does.
You can also use nail polish, just make sure you isolate the pin all the way to the back and up a bit on the rear, apply more then one coat.
Alternatively you can slice the cable length wise for about 2-3cm, then peal the wires out, take a part of the red / black wire out (insulate the endings) and peal it back into the cable.
I did this in multiple instances over the years, everytime with success.
I have an ender 3 v2. the LCD powered but also the webcam stream stopped working (all black) from time to time when switching the printer on off.
I resolved this by carefully stripping my USB cable and cutting the RED wire. As we all know from hollywood its the RED wire that causes the bomb to go off. But its also international standard choice for the 'vcc' or 'power'. If course your cable could be different, but I bet its not. Also cut a few mm away otherwise it might grow back.
Bit of electrical tape to tidy up afterwards
Does anyone know if this backpowering problem can cause static shock when touching the printer ?
I did not implement the tape trick yet, but i'm gonna do it as soon as my current print is over.
I've got a brand new Ender 3 Pro with MeanWell PSU (or at least it's supposed to be, didn't open it yet).
My Pi is a 3B Rev2 with the official power supply i got a that time. I'm beggining to wonder if that's not just my SecretLab gaming chair which is charging me up (it's got that "SoftWeave" Fabric and not the usual fake leather). But i didn't got that much static before getting the printer.
The latter one could be the cause. The printer should be earthed via the power supply and further on the Pi via the USB cable.
The printer has some bare metal parts that are grounded, so the possibility to get discharged at the printer is there. I assume you don't get that static shock when you come right into the room?
I must admit i didn't pay attention to when i was coming back into the room. I just taped the 5v pin and i'm gonna be more aware of those static shock if they still happen.
CR10 V2 (the V2.5.2 board) backpowers, but it still runs. (I'm running one now that's not connected to the printer, it's being powered by a Pi 4.)
Running Cura on the computer that connects to the server has a problem, though. The developer evidently isn't aware that you should open a serial port only when you have to communicate with it. After that, it should be closed.)
I found a relatively easy fix using a dremel with a small burring wheel, and went through the apeture in the top of the USB 2 male. I would recommend this fix for everyone as I almost stuffed my Voxelab Aquila by plugging in a USB supply.
Make sure to mark these non-power cables as I have:
I have discovered that my Ender 3v2 will trigger an alert about a thermal runway — on a printer that it powered off. So now my post-print hygiene includes pulling the USB cable (USB micro B in the year of our lord 2023?).
How interesting, I have several CR-10S machines upgraded to the SKR Mini E3 v3. Only one is giving me random disconnects via wifi. My log shows a variety of DNS issues trying to connect to Obico. The only 2 CR-10S machines are not experiencing any issues. To make my life more interesting, i also have a CR-10S Pro v2 that is on your list. I've learned to power on the machine first, then connect the cable. Thus far, the only thing I have noted on that device is some laggy video.
I've read thru the comments but really haven't seen an "Idiot's guide on how to fix this" in the cable yet. Help =)
